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Home > Home Wiring USA Archive: NEC 1999 > Main Dwelling Design and Options > Wiring a Meter (NEC 1999)

Wiring Utility Controlled Meter-base, Wiring a New Main Service Rated Panel, Installing the Grounding System (NEC 1999)

By Warren Goodrich
Wiring Utility Controlled Meter-base, Wiring a New Main Service Rated Panel, Installing the Grounding System (NEC 1999)

SPECIAL CONCERNS CONTROLLED BY THE UTILITY COMPANIES

Please pay special attention to the particular requirements involving your serving Utility Company. These Utility Companies have specialized rules and requirements that differ from other Utility Companies serving dwellings. Several Utility Companies may serve your area. Research you electric bill and contact your serving Utility Company to gather any specialized rules that will apply to you and your dwelling. Some Utility Companies require that the meter base must be furnished, by you. Some Utility Companies will supply the meter base to you. Some Utility Companies will charge you construction charges, charges to you for them to furnish your meter base to you. Many different rules apply and there seems to be little or no uniformity along these Utility Company requirements depending on locality, type of serving Utility Company, type of construction etc. Almost all of the Utility Companies will expect you to install the meter base, while you are wiring your structure, yet these Utility Companies will most commonly retain control of these meter bases once they energize your dwelling service. You also should confirm who has authority and where the dividing line is between authorities. Usually the Utility Company’s authoritative control includes anything on the line side of that meter base and that authoritative control usually stops within the meter base at the point that load side leaves that meter base. Usually the Authority having jurisdiction [Electrical Inspector] takes authoritative control on the load side of the meter base once that load leaves that meter base itself. Also one point that I might bring up at this time is minimum standards that sets wiring styles for who, Usually a Utility commission’s safety manual controls the Utility Company’s wiring style concerning that wiring within and on the line side of the meter base. Usually the National Electrical Code, International Electrical Code, or a Local or State written and adopted Electrical Code will set minimum safety standards on the load side after it leaves the meter base and including any wiring on the premises buildings or structures.

WIRING THE METER BASE

The line side connection [feeder from the Utility Company’ primary and transformer to inside the dwelling’s meter connection] is to be installed [on the top {overhead fed services} or side {underground fed services] inside the meter base.

The following is for the line side of an UNDERGROUND METER BASE

You may use an underground meter base only if this underground feeder design meets an agreement with your serving Utility Company that you previously approved through that Utility Company. Whether you are upgrading an existing home or wiring a new home the Utility Company has the option to recover their cost of construction. Commonly rules exist that requires the Utility Company to calculate the revenue of the property over a given period of time concerning the projected electrical usage of your home, used by you. The Utility Company may charge you a construction charges for them to serve you underground versus an overhead service. Yet the advantages of less down time due to loss of power in a storm, damage to your home from a storm, and aesthetic value may make the underground installation cheaper or better for your interest in the long run. Be sure to check with your Utility Company and obtain an approval and cost from them for your wiring design and the appointment of time for your service to be energized by the Utility Company, before you start your project, This will confirm that they are serving you overhead or underground, then confirm about construction charges charged to you if any. Be sure to confirm scheduling for the service to be energized by the Utility Company before you start your project. You also must confirm where the meter base is required to be placed on your dwelling. The location of the meter base is controlled, under the authority of the Utility Company. You must also have obtained permits and scheduled electrical inspections from your local Code Enforcement Office before you commence to upgrade your service.

The Utility company most commonly will connect their feeder wire [underground lateral] to that line side of the dwelling’s meter base, within the meter base. Control of that meter base, whether supplied by you or by the Utility Company, will revert to the Utility Company. This meter base will be sealed by the Utility Company and you must not enter that meter base. This meter base is the serving Utility Company’s cash box. The meter inside that meter base is controlling how much they charge you per month for electrical usage. The Utility Company must open that meter base for you if you need to inspect the connections, etc. This is usually done by appointment or emergency response if a hazard exists inside that meter base.

You are expected to supply the down pipe or riser for the Utility Company to utilize during the connection of their feeders to your service. If you are designing an underground service, you should check with the Utility Company concerning whether they require conduit protecting their underground feeders from damage caused by rocks etc. while passing under your driveway or sidewalk, and similar conditions that may cause physical damage to their feeders. This conduit used for protection is normally required to be supplied by you for the Utility Company’s use to protect their feeder.

You are expected to supply and install the feeders from your main service panel to the load side of that meter base. If you are installing individual conductors between your panel and the meter base, your feeders that are running between the meter base and the service panel are required to be protected by a nipple or conduit, while the conductor is routed between your main service panel and the meter base, if individual conductors are used. If you are using a non-metallic sheathed cable, such as type service entrance cable, sized to equal your service size, then further protection such as conduits or nipples are not normally required.

Only two ungrounded conductors [hot] {any color in the rainbow except white, gray, or green} and one neutral conductor [grounded] (white or gray) is normally required for a single phase service, however no equipment grounding conductor [green or bare] is required between the load side of the meter base and the main service panel. Again, normally two ungrounded conductors [hot] and a grounded conductor [white or gray] are required between the meter base and the main service rated panel controlling your dwelling.

NOTE: The equipment grounding conductor, the grounding electrode conductor, and the grounding electrode will be explained later in this pass out.

The following is for
ABOVE GROUND METER BASES WITH A RISER

If this overhead service wiring style of your service equipment is the service design that your serving Utility Company has agreed to connect with you, then the Utility Company will connect to your service entrance conductors that are sticking, at least 3’, out of your weather head. The Utility Company will be running a set of conductors [two insulated and one bare] above ground, through the air as overhead service conductors.

These conductors, twisted together, are called a “service drop”, This “service drop” is supplied and installed by your serving Utility Company. You might notice a drastic size difference between the conductors that you must provide and the size of conductors that your Utility Company uses. This is common due to many variables. One variable is the fact that your conductors are running within your dwelling or structure and the Utility owned conductors are installed completely outside and not within your structure. This difference of being outside and inside a structure provides a major difference in concern for safety due to the location of the conductors in relation to your structure. Another reason for the size difference is whether their conductor or your conductors is aluminum or copper. The resistance of the two metals have a major difference between the two due to the conducting capabilities of the different metals. Another reason is your conductors are contained in a wall or conduit that acts like an overcoat limiting the ability for your conductors to cool, versus the Utility Company’s conductors being in free air allowing rapid cooling as electricity is being used. The final reason for different sizing between your conductors and the Utility Company’s conductors is the fact that you are governed by the NEC and the Utility Company is governed by Utility Safety Code, completely different engineering principles. Although the two codes are similar in goals [safety] but much different in design, magnitude, distance, etc.

Your riser must reach at least 10’ or more above finished grade, measured from the bottom of the drip leg of the service entrance conductors that are sticking out of the weather head, or the point of attachment of the “service drop”, connecting to your service. The “service drop” is usually attached just below the lowest point of your drip leg [the 3’ tail you left hanging out of your weather head. This should make your weather head, mounted at the top of your riser, at least 12’ above finished grade. This weather head height should allow the lowest swag of the overhead service drop passing through the air to maintain a height of at least 10’ above finished grade.

This 10’ minimum height is allowed only if no vehicular traffic can pass under that service drop as required in ARTICLE 230-24-B.

The lowest swag of the overhead service drop must be at least 12’ above finished grade if a vehicle can pass under that service drop as required in ARTICLE 230-24-B. This should make the minimum height of the weather head around 14’ above finished grade.

If the overhead service conductors, service drop, coming from the Utility pole passes over an area that is over a street, road, or alley then that lowest swag area of the overhead service drop must maintain a height of at least 18’ as required in ARTICLE 230-24-B. This should make the minimum height of the weather head around 20’ above finished grade.

Special planning should be considered on the previously described weather head design. If the Utility Company’s pole is high enough to cause their overhead service drop to rise quickly from your overhead riser, then the height of the weather head may be lowered considering the quick rise of the Utility Company’s overhead service drop thus allowing the height of the lowest swag of that drop to still maintain the minimum height required as described above. 12’ should be the least you should consider for the height of your weather head regardless of the angle of the Utility Company’s service drop. Few places are ensured that a vehicle can’t pass under that service drop. [fences, between two close buildings, etc.

If the overhead service riser, or mast, must pass through your roof to maintain the minimum swag height required for the conditions existing with your serving overhead service drop conductors, then your Utility Company’s overhead conductor “service drop” will be expected to be able to be supported by that dwelling’s service riser, or mast. If this overhead service riser, or mast, must support the overhead conductors, then that riser must be substantial enough for it to safely support those overhead conductors during a storm whipping condition of those overhead conductors “service drop” as required in ARTICLE 230-28. This whipping, usually caused by wind during a storm, can cause a great amount of jerking type force against that dwelling’s service riser created by the “service drop” jerking on the service riser [mast]. In my local jurisdictional area both the serving Utility Companies and the Authority Having Jurisdiction [Electrical Inspector] requires at least a 2” rigid or IMC metal conduit to serve as that dwelling’s service riser [mast], if the riser supports the Utility Company’s overhead service drop. This is regardless whether your service size is a 100 or 200 amp rated service. A service larger that 200 amps must utilize a large and stronger riser [mast] than the 2” rigid conduit. ARTICLE 90-4

This riser must also be supported by two straps under the roof line. ARTICLE 346-12-A Be sure not to screw these straps into the siding only. Ensure that you either hit a stud using a one hole mini type strap or screw a unistrut or a board across the two studs and use a two hole strap screwing to that board or unistrut if your riser is between the studs. The service riser passing through the roof must not extend more than 3’ above the roof without installing guy wires or other form of support for that portion of the riser that passes more than that maximum of 3’. ARTICLE 346-12-A These guy wires must be installed in a “V” pattern with the point of the “V” pointing toward the Utility Company’s pole, and the open part of the “V” opening away from the Utility Company’s pole.

The minimum clearance from the roof line for the final overhead span connected to your service mast must be at least 18” between the roof and the service drop. ARTICLE 230/24/A/exc4

Be aware that the CABO Building Code requires that the area where the riser passes through the roof line must be sealed to be weatherproof.

A little trick of the trade revealed;

Most hubs mounted to the top of a meter base that is designed to screw the metal riser conduit into the meter base is designed in the form of an eccentric. This means that the hole of the hub is offset allowing the hub to be twisted in a circle to aid in positioning your riser the way you need it, in order for that riser to be straight to the wall or structure.

MOUNTING THE METER BASE

THE CENTER OF THE METER NORMALLY MUST BE 5' 6" FROM FINISHED GRADE [EARTH] regardless whether your service is overhead or underground designed.

The following is for an underground meter bases without a riser

INSTALLING THE METER BASE DOWN-PIPE

Please keep in mind that most areas located below the height of a meter base is considered to be subject to physical damage. The only exception would be if a substantial structure is placed in front of the meter base area. This obstruction would have to be approved by the Utility Company and the Authority having Jurisdiction [Electrical Inspector].

In order to install the down pipe from the meter base to below earth level as required by the NEC, measure from the bottom of the meter base to the ground [earth] and add 18” to that measurement. TABLE 300/5 Now cut a section of 2” to 3” Sch 80 PVC depending on the instructions concerning the Utility Company rules. This can vary often due to the different size feeders each different Utility Company may install. Minimum size Sch 80 PVC would be 2” ARTICLE 347/2/F or 2” rigid conduit ARTICLE 346/2/A or 2” intermediate metal conduit [IMC] ARTICLE 345/3/A cut to a length equal to the measurement you discovered to be 18” or more than the distance from the bottom of the meter base and the finished grade of earth. Now glue a terminal adapter to the end of the PVC conduit, add a locknut and a plastic bushing ARTICLE 30O/4/F to the terminal adapter, if PVC is used. Be aware that each Utility company will vary the required size of this down pipe you must furnish for them to install their underground lateral feeders.

If you are using Rigid or IMC then you must install two locknuts and plastic bushing ARTICLE 30O/4/F on the top end and you must also install a plastic bushing on the bottom of these metal conduits.

Once you have made the down pipe for the Utility Company to use to protect their underground conductors feeding your structure [“service lateral”], you may set the down pipe on top of the ground leaning against the side of the meter base. The Utility Company will usually want to install this down pipe for you while they install their “service lateral”.

Some Utility Companies have a rule that no meter may be installed on the back of a new dwelling. The methods of recording each premises electrical usage can now vary from shooting the meter with an electronic measuring device read from the road, to telecommunication by computer and phone connections, to a man coming to the house to visually read the meter and more methods are also available. The Utility Company will meet with you and tell you where they want that meter base installed and how at your request.

INSTALLING THE UNGROUNDED [HOT] FEEDER CONDUCTORS SIZING YOUR SERVICE RATED PANEL OR MAIN DISCONNECT

The following is a format for calculating the demand load calculation of a single family dwelling or duplex, that is required to be performed by you in order to provide you with the ability to know the minimum main service size of your dwelling as required by the NEC. Once you know the minimum service size then you can accurately decide how much larger than the minimum you want to size your service.

Please keep in mind that in generic terms and as a protection from causing confusion to you due to a possible lack of knowledge this subject, you can picture both “watts” and “volt amps” as approximately the same thing. For most construction activity there is normally little difference between the two terms. Now for electronic circuits or power factor data, etc. there is a definite difference between the two terms. However for this application we are dealing in enough volt amps or watts to deal with more total amps where the variables between the two terms make little difference.

TABLE 220/3/A General lighting load = 3 volt amps times the outside dimensions of your dwelling not counting garages or unfinished basements.

DO NOT INCLUDE THE ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING FOR PREPARATION ONLY.

ARTICLE 220/16 Add in 3,000 volt amps for your small appliance branch circuits as required in the kitchen for your dwelling. 1,500 volt amps for each small appliance branch circuits. Definition of a small appliance branch circuit is any receptacle serving the kitchen, nook, dining, and pantry.

DO NOT INCLUDE THE ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING, for PREPARATION ONLY.

ARTICLE 220/16 add in 1,500 volt amps for your laundry in the dwelling whether you have a laundry or not, it is required to be in the demand load calculation. This is no matter how many receptacle are in your laundry.

DO NOT INCLUDE THE ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING FOR PREPARATION ONLY.

Now add the above together to get the total non-adjusted general lighting load of your dwelling.

DO NOT INCLUDE THE ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING FOR PREPARATION ONLY.

ARTICLE 220/11 Now we want to take that total non-adjusted general lighting load and apply the general lighting demand factors to your totals of the above non-adjusted general lighting load that you just calculated. This application of the general lighting demand load factor is intended to adjust your total non-adjusted general lighting demand load calculation by factoring in adjustments for intermittent activity you are expected to experience while using the dwelling’s general lighting. It is expected that not all general lighting will run at the same time for extended periods of time.

DO NOT INCLUDE THE ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING FOR PREPARATION ONLY.

In order to apply the demand factors to your general lighting load, take your total non-adjusted general lighting load, that you calculated, and subtract the first 3,000 volt amps from that non-adjusted general lighting load. Now set that 3,000 volt amps that you deducted aside in the right hand column for future use in latter calculations. Now take the answer concerning the remainder of your total non adjusted demand load that you obtained after subtracting the first 3,000 volt amps and multiply that remainder times 35%. This reduces the total general lighting load to a smaller figure adjusting that total general lighting load thus accounting for the expected diversity or intermittent use of the general lighting of your dwelling, by the 35% adjustment. Now set the answer to that multiplication times the 35% and install that answer to that right hand column for the final answer calculation also.

These two answers you installed in the right hand column accounts for the expected actual use considering your expected intermittent use, or diversification allowance. It is generally felt that you probably will use the first 3,000 volt amps at 100% then any more general lighting that you would use would be reduced to the 35% factor that we implemented into the calculation. You now have the TOTAL ADJUSTED GENERAL LIGHTING DEMAND LOAD. The total non adjusted general lighting calculations that you came up with are set aside and no longer used in further calculations of your demand load calculation sizing the main service of your dwelling. You will only use the total adjusted general lighting demand load found after applying the adjustments allowed in ARTICLE 220/11 for demand factoring.

Now write down in a far right column the answer you received by adding the two adjustments above in your calculations for the total ADJUSTED general lighting demand load. Use this as your new starting point. Remember do not add in any of the figures that you used to get that calculated total non - adjusted general lighting demand load. Just start with the adjusted general lighting load.

INCLUDE THIS ABOVE SUBTOTALED SECTION IN THE FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS THE TOTAL ADJUSTED GENERAL LIGHTING LOAD OF YOUR DWELLING.

ARTICLE 220/21 Now find the total amp rating found on your name plate of your furnace and your air conditioner. Consider, with the exception of heat pump systems, that you will not use both the heating and the air conditioning at the same time. Therefore you may throw out the smallest of the furnace or air conditioning loads as long as your heating system is not a heat pump system. You will add to the running total just the largest load.

DO NOT INCLUDE THE ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING FOR PREPARATION ONLY.

SPECIAL NOTE ON HEATING AND AIR CONDITIONING LARGEST LOAD;

If you are using a heat pump system that is designed to utilize both the outside air conditioner as a heat pump and a furnace as an assist heating source. You must include both the air conditioner and the furnace as the heating or air load, because both are expected to run at the same time while heating.

Now add this heating, or air conditioner [load whichever is largest omitting the smaller load] or both the heat pump and furnace if heat pump system, to the far right column below the total adjusted general lighting demand load.

INCLUDE THIS ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING.

ARTICLE 220/17 Next you will want to make a list of all fastened in place appliances, and their name plate rating in amps that your fastened in place appliance is rated to need. This would include any appliance permanently installed and connected with a Romex connector.

A partial list of fastened in place appliances found in a dwelling would be as follows;

electric water heater, water heater circulating pump, garbage disposals, dishwashers, microwaves that have a microwave cabinet installed for a designated place for your microwave, a range hood or microwave hood combination, a whole house fan, paddle fans, hot tubs, whirlpool tubs, sewage lift stations, sump pumps, built in trash compactor. There are other loads that will fit into the fastened in place appliances. Just ask yourself if your appliance has a designated permanent place for that appliance.

DO NOT INCLUDE THE ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING FOR PREPARATION ONLY.

Now separate the 220 volt appliances from the 125 volt appliances and take the total amps from your 220 volt list of fastened in place appliances and multiply the total amps by the 220 volts that the appliances are designed to be using to run. Then take the total amps from your 125 volt list of fastened in place appliances and multiply the total amps by 125 volts that the appliances are designed to be using to run. Once you have converted by calculation all fastened in place appliances into volt amps or watts then add the total volt amps of the 220 volt rated appliances and the total volt amps of the 125 volt rated appliances together.

DO NOT INCLUDE THE ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING FOR PREPARATION ONLY.

Now once you have made that list of fastened in place appliances and made the calculations converting the total loads to volt amps, then count up the total number of individual appliances that you listed regardless whether they were 220 volt rated or 125 volt rated. If you have three or less fastened in place appliances then you must enter into your running total that total at 100% in volt amps on the far right of your page to be included in the demand load, without further calculations. If you have 4 or more fastened in place appliances then multiply the total volt amps times 75%. This 75% answer will be the adjusted fastened in place appliance load that you would enter into your running total on the far right of your page to be included in the demand load calculation.

INCLUDE THIS ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING.

SPECIAL NOTE ON FASTENED IN PLACE APPLIANCES;

This 25% reduction you calculated by multiplying your total volt amps of your fastened in place appliances times 75% gives you an allowance considering the probability that not all fastened in place appliances will run at the same time if you have more than three fastened in place appliances. The NEC suspects that you will likely run three appliances at the same time but not likely to run four or more at the same time.

ARTICLE 220/18 Now enter in your electric clothes dryer, if electric and not gas, at 5,000 volt amps if your dryer volt amp rating is unknown, or if your dryer volt amp rating is smaller than 5,000 volt amps. If your dryer volt amp rating is larger than 5,000 volt amps then use the name plate rating but only if that name plate rating is more than 5,000 volt amps. No further de-rating is allowed for more than one dryer unless you have 5 electric dryers or more. More than 5 dryers would be highly unlikely in a dwelling setting. If you have a gas dryer then omit this step, ignoring the dryer section, your laundry load entered at the beginning of this format included the use of a gas dryer at that point therefore if a gas dryer is used no further load in volt amps must be added.

INCLUDE THIS ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING.

ARTICLE 220/19 Now enter in your electric range, if electric and not gas, at 8,000 volt amps for one electric range if your electric range name plate rating is less than 12,000 volt amps or 12 Kw. Most residential electric ranges will fall in this less than 12,000 volt amp rating. If you have a second electric range in you dwelling then use 11,000 volt amps instead of the 8,000 volt amps. This gives you an adjustment factor if more than one range is used in a dwelling for canning etc. If you have more than two electric ranges which would be highly unlikely then refer to TABLE 220/19 to find the demand factor rating for the number of ranges you have in your home.

INCLUDE THIS ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING.

ARTICLE 220/14 and ARTICLE 430/24 Your motors were included in the fastened in place appliances. Therefore to meet the requirements of these two NEC articles we just have to find the largest motor load in volt amps converted from amps by multiplying the amps by the voltage rating of the motor. Be aware that the horse power rating of a motor being the largest in the dwelling will not necessarily make this motor the largest motor load. You must use the largest full load amp rating of the motor. This is a common confusion because a smaller horse power motor rated to use 125 amps though smaller in horse power than a 220 volt rated motor can very well require a larger amp load to run that 125 volt rated smaller motor than the larger horse power rated 220 volt motor with smaller amp rating.

Now take that converted volt amp rating of your largest motor load that you found calculated in volt amps instead of amps and multiply that volt amp rating time .25 then add this answer in volt ampsof your largest motor load to into your running total on the far right of your page to be included in the demand load calculation. This calculation will increase you largest motor by 25% as required in ARTICLE 220-14.

INCLUDE THIS ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING.

Now add all the totals in your far right column together as a total demand load of your dwelling in volt amps. Starting with your total ADJUSTED general lighting, your heating or cooling, your adjusted fastened in place appliances, your adjusted electric dryer, your adjusted electric range, and your 25% increase of your largest motor together finding a grand total in volt amps

INCLUDE THIS ABOVE SECTION IN FINAL RIGHT HAND COLUMN CALCULATION TO BE ADDED AS DEMAND LOAD OF DWELLING.

Now divide your total demand load of your dwelling in volt amps by the applied voltage 240 volts.

That answer is your total demand load of your dwelling in amps thus requiring your minimum service size for your dwelling. You may and most do adjust to a larger main service panel size in amps than the minimum required. This is commendable, but at least now you know exactly how much more than the minimum service size you are installing. In my opinion that action would be much better than a guess, wouldn’t you think?

As a final adjustment you must refer to the NEC ARTICLE 240/6. This article list the normal over current protective device sizes accepted by the electrical industry. An over current device is a fuse or breaker that you normally find in a dwelling. The following are listed as normal accepted sizes 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000. Your total demand load calculation may land between one of these size over current devices [fuse or breaker]. You may adjust the fuse size to the next larger fuse or breaker size compared to your answer if your demand load or conductor ampacity lands between two normal breaker or fuse sizes found in ARTICLE 240/6. ARTICLE 240/3/B

SIZING YOUR FEEDERS SERVING AS YOUR SERVICE ENTRANCE CONDUCTORS TO YOUR MAIN PANEL FROM THE POINT OF CONNECTION OF THE SERVING UTILITY COMPANY.

The hot service entrance conductors for a dwelling may be sized by the chart found in TABLE 310/15/B/6 The following wire sizes are approved by the NEC to serve as the service entrance conductors supplying the main service panel or disconnect in your dwelling containing your main service over current device [main breaker or fuse size].

#4 copper=100 amp
#2 aluminum=100 amp
#2 copper=125 amp
1/0 aluminum=125 amp
#1 copper=150 amp
2/0 aluminum=150 amp
2/0 copper=200 amp
4/0 aluminum=200 amp
3/0 copper=225 amp
250 kcml aluminum=225 amp.

There are more ampacity ratings in the chart found in the NEC TABLE 310/15/B/6, but the ones listed should hit what you are looking for in amp size. The following conductors are approved for use in the wire sizeslisted above forsingle-phase dwelling services and feeders. Conductor Types RH, RHH, RHW, RHW-2, THHN, THHW, THW, THW-2, THWN, THWN-2, XHHW, XHHW-2, SE, USE, USE-2 are approved for use with the above ampacity ratings where dwellings service entrance conductors are involved.

As I said previously the hot service entrance conductors for a dwelling shall be sized by the chart that has been provided to you above found in the 99 NEC. This chart tells is that the sizes in that chart are allowed to be used for use, serving a dwelling unit.

This does not include non residential service conductors for use in structures not used as a single phase dwelling setting. The hot service entrance conductors for non-residential structures shall be sized by the chart found in TABLE 310/16 of the NEC.

DESIGNING A SERVICE FOR YOUR DWELLING WHEN A SERVICE LARGER THAN 200 AMPS ARE REQUIRED

The two most common service sizes are 100 and 200 amp service panels or main disconnects. If a 300 or 400 amp service is needed it is common to use a parallel main service panel using a 100 amp main service rated panel and a 200 amp main service rated panel set side by side to create a 300 amp paralleled service both being fed separately from the meter base and serving your dwelling, or two 200 amp main service rated panels to create a 400 amp paralleled service both being fed separately from the meter base and serving your dwelling. If you opt to parallel two panels to make up the total amp service rating that you desire, then you will have to install a meter base that is rated high enough in amps to carry the total of the two panels in amps that were paralleled. TABLE 310/15/B/6 You are allowed to install up to 6 main service rated panels or disconnects to serve a structure as long as they are all grouped together to make a grouped main service rated system. ARTICLE 225/33

However if you have an overhead service, with a riser, then the service conductors going up that riser found on the line side of the meter base must be run by you. This set of service entrance conductors going from the line side in a meter base through the overhead service riser that is tailed out for the utility company to connect with, must be sized by the total amp load of the combined main breakers or fuse sizes of the paralleled panels. TABLE 310/15/B/6

Each panel would use the following service entrance conductor size ratings for each individual main service rated panel equal to that panel’s main over current device [fuse or breaker] rated in amps to size the ungrounded [hot] conductors. These same following ratings may also be used to size the service entrance conductors going up the riser on an overhead service system and sized by the total amp rating of all main over current devices [main breakers or fuses] when their loads are being carried by that same service entrance conductor going up that riser in parallel. The chart shows that you may use a # 4 copper or a #2 aluminum conductor as service entrance conductors serving your dwelling’s 100 amp service panel or main disconnect. The chart also shows us that you may use a #2/0 copper or #4/0 aluminum as service entrance conductors serving your dwelling’s 200 amp service panel or main disconnect. TABLE 310/15/B/6. If you are carrying two panel on one feeder then the combined load must be added together then refer to TABLE 310/15/B/6

SIZING THE NEUTRAL SERVICE ENTRANCE CONDUCTOR

The neutral conductor size must not be smaller than the grounding electrode conductor. The grounding electrode conductor must be sized by TABLE 250/66 of the NEC. The neutral conductor must have the ampacity to carry the unbalanced load between the two ungrounded conductors [hot conductors]. The unbalanced load of the neutral can be calculated in your demand load calculation as required in ARTICLE 220/22 of the NEC. You commonly may choose an option that used to be written in the NEC allowing the neutral conductor to be the same size or no smaller than 2 sizes smaller than the ungrounded conductors [hot conductors] being used as your service entrance conductors. This method of sizing the neutral the same size of not more than 2 sizes smaller than the ungrounded service entrance conductors [hot conductors] can commonly be used with less chance of the sizing of that main neutral service entrance conductor to be challenged by the Electrical Inspector, because it would usually be plenty big enough to meet the minimum neutral sizing found in the demand load calculation. TABLE 3lO/15/B/6 AND 220/22. Check with your local AHJ [electrical inspector] to confirm that he will accept that form of neutral conductor sizing, before you start you work.

Sizing a service entrance neutral conductor by an unbalanced load calculation would require adding all of the following; 120 volt loads plus an adjusted demand load of 240 volt loads that utilize a 120 volt load provided by the 240 volt circuit, such as ranges and dryers. ARTICLE 220/22. This form of calculation can be quite complicated. You would probably need local guidance to perform the neutral demand load calculation to size your neutral service entrance conductor.

The format to size a neutral service entrance conductor is approximately as the following; The adjusted general lighting load is a 120 volt load creating a load on the neutral service entrance conductor. This adjusted general lighting load would by your total square feet of the dwelling [outside dimensions] multiplied by 3 volt amps found in TABLE 220/3/A of the NEC. Then add in the two 20 amp small appliance branch circuits @1,500 volt amps and the one 20 amp laundry branch circuit @ 1,500 volt amps. Then add those three numbers together and subtract 3000 volt amps. Multiply that answer times 35% and add the 3,000 volt amps back to the answer of your multiplication. Then add any 120 volt heating system such as gas furnaces @ 100%. Then add 70% of the 5,000 volt amp load of the dryer and 70% of the 8,000 volt amp range. Now add up all of the 120 volt loads found as fastened in place appliances at 100% if 3 or less fastened in place 120 volt appliances or at 75% if 4 or more fastened in place 120 volt appliances. Now add that total fastened in place appliance total after the range was added. If you add all the above grounded loads found on the main service entrance neutral conductor, then you may size your main service entrance neutral conductor by that total unbalanced neutral load calculation. NEC Chapter 9 TABLES AND EXAMPLES You may take a further reduction of 30% of that main service entrance neutral conductor for that portion of the that unbalanced neutral load that is over 200 amp in total amp rating, by multiplying that main service entrance neutral conductor total unbalanced neutral load found to be over 200 amp by 70%. Only do this if your total unbalanced neutral load is rated over 200 amps. ARTICLE 220/22

After reading the above you should understand why I suggested just to size your neutral service entrance conductor either the same size as your ungrounded [hot] service entrance conductors or not more than two sizes smaller than those ungrounded [hot] service entrance conductors. You should have little question from the Electrical Inspector if you size your neutral service entrance conductor not more than two sizes smaller than your service entrance conductors.

MAIN OVER-CURRENT DEVICES LOCATION FOR THE MAIN SERVICE

In this jurisdiction, if you install the main service distribution panel that contains the main over current device [ main breaker or fuse] within 3’ of entering the structure with the feeder conductors, then a main over current device [main breaker or disconnect with fuses] will not be required outside the dwelling. In another nearby jurisdiction the maximum distance is 10’. This distance varies within different jurisdictions.

The main over current device [main breaker or disconnect with fuses] may be inside the distribution panel serving as a service rated main service distribution panel, as long as the nearest point of entrance requirement is met.The NEC states that you may install the main over current device [main breaker or fused disconnect] either outside and weatherproof rated, or inside and non-weatherproof rated at the nearest point of entrance, of the dwelling. The judgment or ruling dictating the distance you may go once you enter the dwelling or crawl space before you must install your main over current device [main breaker or disconnect with fuses] and still meet the maximum distance requirement of “nearest point of entrance” stated in the NEC is under the authority AHJ [electrical inspector]. ARTICLE 230/70/A andARTICLE 90/4 The electrical requirement stated “nearest point of entrance” is designed to limit the distance that those feeders may reach between the main over current device [main breaker or disconnect] and the meter base. The reason this limit is controlled is because your feeders between the meter base and your main over current device are not protected by an over current device [breaker or fuse] except on the load side of those feeders. If a short circuit appeared with those feeders between the meter base and the main over current device, they would just get hot and cook causing a melt down or fire. This is because the main over current device is at the end of that feeder and that over current device would not register or pick up a short in those main service entrance conductors [feeders] ahead of the location of that over current device. That main over current device would not be carrying the load of those feeders found between the meter base and the main over current device [main fuse of breaker]. Therefore the main over current device would not have a means of registering that short or being able to shut off the power melting down or causing the fire due to those shorted feeders.

DEFINITION AND INSTALLATION DESIGN OF A SUB-PANEL

Definition of a sub-panel [non service rated panel] = A panel not deriving its power source directly from the serving utility company or a separately derived power source [generator, or transformer]. One type of sub-panel is a sub-panel that is deriving its power source through a main service rated distribution panel. A second type of sub-panel is a sub-panel that is deriving its power source through a main service rated disconnect. A third type of sub-panel is a sub-panel that is deriving its power source through another sub-panel that is a slave of a main service rated panel or disconnect. This third type of sub-panel is a sub- panel of a sub-panel. Any way you put it a sub-panel is a panel that is a slave of another main panel or main disconnect, or another sub-panel. This sub-panel [slave of another panel, whether main or sub] is controlled by an over current device {fuse or breaker} located in another panel or disconnect ,serving that sub-panel, that will shut off that entire sub-panel. Disconnects that serve as a form of disconnect controlling a single appliance such as hot tub, furnace, a/c, water heater is also considered a form of a sub-panel.

When dealing with the National Electrical Code book you will not find the term sub-panel. When dealing with the rules of the NEC you must refer to a sub-panel as a non-service rated panel. Non-service rated panels is the only phrase recognized by the NEC when referring to any type of sub-panels. ARTICLE 250/24/A/5

If the distribution panel is a non-service rated panel [sub-panel], fed from the load side of a main service rated disconnect or main service rated panel, or other non-service rated panel [sub-panel of a sub-panel] then you are allowed to use a main lug only panel. This main lug only panel [no main breaker but is a main lug only, in a non-service rated panel] is allowed because this non-service rated panel is not service rated, therefore the six disconnect rule ARTICLE 230/71 and ARTICLE 225/33 requiring a main breaker in a main service rated panel or separately derived power system [generator or transformer fed service] does not apply to non-service rated panels [sub-panels]. You already have a main form of disconnect [breaker] found in the panel that is serving the power to that non-service rated panel [sub-panel]. This allowing main lugs and without a main breaker in that non-service rated panel [sub-panel] is true no matter if you have as many as 40 circuit breakers in that non-service rated panel [sub-panel]. The main shut off of this non service rated panel [sub-panel] is found in the panel that supplies power to that non-service rated panel [sub-panel]. ARTICLE 250/33

The non-service rated panel [sub-panel] must be fed with three wires if 120 volt rated or 4 wires if 240 volt rated. The non-service rated panel must be fed with either one or two ungrounded conductors [hot conductors {line 1 or line 1 and line 2}].(These ungrounded [hot] conductors may be any color of insulated material in the rainbow except white, gray, green, or bare) This same non-service rated panel must also be fed with one grounded conductor (This grounded conductor’s insulation must be either white or gray) [This grounded conductor would be called a grounded leg if the non-service rated panel is 120 volt fed {line 1 only and with the grounded conductor and grounding conductor [equipment grounding conductor]} or This grounded conductor would be called a neutral if the non-service rated panel is fed by two ungrounded conductors which would make it 240 volt using both hot conductors {line 1 and line 2 and the grounded conductor [neutral] and the equipment grounding conductor}]. All non-service rated panel must be fed with an equipment grounding conductor (This equipment grounding conductor must be either green or bare) no matter whether this non service rated panel is fed with one or two hot conductors, or even whether this non-service rated panel is fed with a grounded conductor [neutral or grounded leg] the equipment grounding conductor must also be installed feeding this non-service rated panel (sub-panel).ARTICLE 250/142/B

The above requirements have been confusing to many. Many people in the industry have been confusing the six disconnect rule for a main service rated panel with the requirements of a non-service rated panel [sub-panel]. ARTICLE 230/71 You may or may not use a main breaker in a non-service rated panel, your choice on this decision. This is your choice to make. If you install a main breaker, fuse, or disconnect in your non-service rated panel, then that main breaker, fuse, or disconnect is called a supplementary fuse, breaker, or disconnect. This is because you are already required a fuse, or breaker, and disconnect to be located at the line side of the feeder serving your non-service rated panel, and located in the panel supplying the power to that non-service rated panel. This supplementary breaker of fuse or form of disconnect does not have to be marked in amp rating nor is their a limit to amp rating of this supplementary breaker or fuse, as long as the feeder is protected by a breaker or fuse serving that non-service rated panel and can be used as the disconnecting means for that non-service rated panel, and the disconnecting means and fuse or breaker protecting the feeders of that non-service rated panel is located in the panel that is supplying the power to this non-service rated panel. ARTICLE 230/71 and ARTICLE 240/10 and ARTICLE 240/60

If you are installing a panel to a separate [detached] building, fed from a main building ARTICLE 250/32, a main breaker or disconnect may or may not be required. This may or may not be required depends on the design of your grounding system. This statement raises a large disagreement with my thoughts in this statement. A rather detailed and lengthy discussion was presented concerning whether a detached structure must have a main breaker and have a grounding electrode installed in that detached structure. My belief is that if you opt to use 250-32-B-1 then you are carrying the equipment grounding system from the serving building to that second detached building making both buildings as one building fed from a common service. Many or most disagree with this stance and belief saying a grounding electrode must be installed at that second building and a main breaker must be installed. I can not argue with their thought that if a grounding electrode is installed at that second building the wiring design would be better or safer. I have publicly conceded that adding the grounding electrode at that second building may be a better design. Check with your AHJ [electrical inspector] to confirm his ruling on the subject before you start your project feeding a detached structure from a serving structure. I believe that to be your safest path to proceed.

ASSOCIATED DETACHED STRUCTURES AKA. DETACHED GARAGES, BARNS, SHOPS, ETC.

There is a section in the NEC that is explicit to supplying two or more buildings or structures from the same common service. The words common service and supplying two or more structures are the key elements in the following wiring design. Just because the two buildings are not connected as one structure physically, these to buildings may still be considered as one structure electrically. This designation of joining the two buildings as one electrically would depend on whether these to buildings are considered as one structure electrically, solely on whether you have an equipment bonding connection between the two buildings. This equipment bonding connection can be in the form of a gas line, water line, equpment grounding wire in a phone line, even a metal heat duct would make the two buildings as one building electrically, in my opinion. The concern is to protect the wiring design from creating two electrically non-connected grounding sources to the same buildings being served by one service and sharing one grounding electrode system. The intent as I understand it is to ensure that there is no difference of potentiality between any pieces of non current carrying metal [substantial pieces of metal only]. A difference of potentiality would be when you have two pieces of metal that is connected to earth by two different and separate grounding electrode systems [ground rods, etc.] If two pieces of metal have two separated grounding electrode systems, and these to pieces of metals are within reach of each other by on person touching both grounding electrode systems, the two grounding electrode systems can have different levels of potential path to earth ground. These two different levels of potential, between grounding electrode systems, will suddenly equalize if contact is made between the two separated grounding electrode systems. If a person’s body is that contact between the two separated grounding electrode systems, a rush of current will pass through that person’s body possibly causing severe injury or death, depending on the extent of the difference of potential between the to separated paths to earth’s potential.

Again this stance in my belief has been strongly contested by many very qualified people in the electrical field as to what ARTICLE 250-32-B-1 actually says and requires. [The wiring design in ARTICLE250-32-B-1 is designed to include an equipment grounding conductor installed with the feeder between the two buildings, thus carrying the grounding electrode system from the first building to the second building]. It is my belief that installing a new grounding electrode system, physically located at that second building fed by a common service from a main service rated panel located in a main building is not required by the NEC. However, after the lengthy discussion and the strong arguments against my interpretation of this NEC article, I would like to say that I feel it would be fine, if not a better design, to install a new grounding electrode system physically located at that second building augmenting that existing grounding electrode system carried to that second building from the first building, by making both systems as one system, and electrically joined. The equipment grounding conductor installed with the feeders between the two building can be joined with the new grounding electrode system physically installed at that second structure only as long as you keep the neutrals and grounding conductors separated in that sub-panel serving in that second building. However you must join the new grounding electrode system added at that second building to the existing grounding electrode system that you carried with the feeder from the first building into that second building outside that second structure and before those two grounding electrode systems enter that second structure. This joining of the two grounding electrode systems thus making both grounding electrode systems as one grounding electrode system outside before they enter the second structure, then allows only one grounding electrode system to physically enter that second structure.

A DETACHED STRUCTURE THAT IS BEING FED BY A FEEDER THAT IS INCLUDING AN EQUIPMENT GROUNDING CONDUCTOR SUPPLIED FROM THE MAIN HOUSE OR STRUCTURE.

If you are running an equipment grounding path between the two buildings [water pipes, etc.] or you have an equipment grounding conductor ran with the feeders serving that detached structure with power from your main house to your detached structure, then a main breaker or disconnect is not required. ARTICLE 250/32/B-2 and ARTICLE 225/32 and ARTICLE 230/70 and ARTICLE 230/71

If an equipment grounding path is found between the two buildings [metal water pipe, etc.] or an equipment grounding conductor is run with the feeders serving that building from your main house, then none of these grounding sources including the equipment grounding conductor [green or bare] run with the feeders serving that detached structure are allowed to be in contact with the grounded conductor. [neutral or grounded leg {white or gray}] If you have a grounding path between the two buildings, no matter the type, you will have to install, or use, a neutral bar for grounded conductors [white or gray] that is isolated by plastic from the metal of the panel box and from any equipment grounding source [metal water pipe coming from the main house or in contact with earth for 10’ or ground rod] or equipment grounding conductor [green or bare].

The above wiring design sharing the equipment grounding source of the main structure [ground rod, etc.] makes this detached structure the same as one entity or structure, electrically.

Again the key word in the rule ARTICLE 250/32/B/2 speaks of two structures using the SAME COMMON SERVICE ! This rule is explicit for two or more building served by the SAME COMMON SERVICE coming from the main dwelling or structure. This rule does not make or allow a stand alone structure that is served by the SAME COMMON SERVICE to be a service rated panel, disconnect or even a service itself, just two buildings served by the same service [one service] not a new separately derived service at the second building. No other rules apply in this situation, just the written rules of this article. Now on the load side [once you leave the interior] of the panel in the second or third building you would go back to using all other code articles as in the main dwelling or structure. Explicit for the use of that second or more building or structure. Example; detached garage, horse barn, storage building, etc.

The above wiring style of the panel in the second or more buildings served by the same main structure’s SAME COMMON SERVICE would make that panel in the second or more buildings or structure a NON-SERVICE RATED PANEL [sub-panel] of the main buildings service rated panel thus the neutrals and equipment grounding conductors must be separated on separate bars in that panel located in that second structure.

A DETACHED STRUCTURE THAT IS BEING FED BY A FEEDER THAT DOES NOT INCLUDE AN EQUIPMENT GROUNDING CONDUCTOR OR GROUNDING PATH SUPPLIED FORM THE MAIN HOUSE OR STRUCTURE.

If you DO NOT have a non current carrying metal grounding path [metal water line, etc.] and are NOT running an equipment grounding conductor with the feeders serving that detached structure with power from your main house to your detached structure [one or two hot conductor {not white, gray, green or bare} and with those two hot conductors you have a neutral or grounded leg {white or gray} but NO equipment grounding conductor {green or bare} ran with that feeder between the two buildings], then a main breaker or disconnect must be provided either outside or nearest point of entry inside your detached structure. ARTICLE 250/32/B/2 and ARTICLE 225/32 and ARTICLE 230/70 and ARTICLE 230/71

You must then install a new grounding electrode system [ground rod, etc] to serve that building because you have no equipment grounding connection between the two buildings. The above wiring style of the panel in the second or more buildings served by the same main structure, even though it is the same common service, would make that panel in the second or more buildings or structures a SERVICE RATED PANEL and this service rated panel found in that second or more buildings or structures must be provided with a new grounding electrode system [ground rod, etc.] You must also marry both the grounded [white or gray] and the equipment grounding [green or bare] together using a bonding jumper making both grounded [neutral] and equipment grounding the same as one entity inside that panel and in contact with each other and the metal of the service rated panel also must be in contact with these grounded and grounding bars located within that panel.

Now on the load side [once you leave the interior] of the panel in the second or third building you would, again, go back to using all other code articles as in the main dwelling or structure. Explicit for the use of that second or more building or structure. Example; detached garage, horse barn, storage building, etc.

SPECIAL NOTES

LOCATIONS THAT YOU MAY NOT MOUNT A DISTRIBUTION PANEL

You must not install a distribution panel, disconnect, etc., whether service rated or non-service rated panel [sub-panel] in or over the following areas or equipment; In a storage area or in a clothes closet. ARTICLE 240/24/D in a bathroom, ARTICLE 240/24/E in a crawl space, ARTICLE 110/26/A/1 in a recessed area over a ledge or concrete or dirt shelf found in partial basements, ARTICLE 110/26/A/1 in an area with less than 6 ½’ of head room ARTICLE 110/26/A unless panel is not rated more than 200 amps and is installed as a service upgrade in an existing dwelling, over any permanently mounted counter space or work bench, ARTICLE 110/26/A/1 over any large appliances such as laundry equipment, cabinets, vanities, sinks, tubs, water pumps, water softeners, sump pump holes, water heaters, and the like. ARTICLE 110/26/A/1 You must maintain at least 3’ of clear approach with no obstructions that is not electrical in nature either below, in front of, or above that distribution panel. ARTICLE 110/26/E You must maintain a dedicated width of at least 30” in which the panel may be mounted anywhere within that 30” wide dedicated space. ARTICLE 110/26/2

CLEARANCE REQUIREMENTS OF A RISER / METER / OR PANEL FROM OPENINGS

You must maintain at least 3’ of clearance as the crow flies between the RISER’S WEATHER HEAD DRIP LOOP “ONLY” AND ANY SERVICE DROPS [WIRES COMING TO THE BUILDING THROUGH THE AIR at the top of an electrical service riser and weather head where the utility company or a private connection is made. Any of the following examples must maintain that required 3’ clearance from that drip loop or service drop [wire coming through the air]; from the sides and bottom of any window that opens, from any door that opens, from any elevated openings such as balconies or hay loft doors. You may install the service riser and weather head drip loop less than the 3’ clearance if mounted at the top of a window, even if that window opens. The idea is to keep those connections where the service drop [wire coming to the structure through the air] and your service conductors coming out of your weather head out of reach of unqualified personnel. ARTICLE 230-9

You may install a distribution panel, or meter base, conduit or service entrance cable right next to any door, window, wall, etc. as long as the panel door will open at least 90 degrees, and there is a 30” dedicated space for that panel or disconnect. You just have to be concerned about the 3’ clearance away from the sides or bottom of any window or within reach of any door, platform, loft etc. from any conductors associated to that drip loop that are not protected by a non metallic sheath or conduit. TABLE 230-9

You must maintain a clearance of 6’ from any gas appliance or gas meter, or gas or fuel vent of a gas or fuel storage tank with any electrical service box that will open and is without a utility company’s seal protecting that box from being opened. THIS RULE IS USUALLY FOUND IN YOUR SAFETY STANDARDS.

You may install a distribution panel or service rated panel in a kitchen, dining room, living room, bedroom, utility room, garage, in basements, dens, or even outside {if waterproof for outside installations in wet locations} as long as you maintain the required clearances and accessibility mentioned above. You must maintain the clear approach, dedicated width, unlocked access, and without non-related obstructions. ARTICLE 110/16

INSTALLING THE GROUNDING ELECTRODE SYSTEM, AND THE GROUNDING ELECTRODE CONDUCTORS.

Definition of a grounding electrode conductor is that sole connection between the grounding electrode system [approved contact with earth] and the dwellings service. [meter base or main service disconnect or panel]. ARTICLE 100

An approved grounding electrode system is listed in ARTICLE 250/50. The grounding electrode conductor is normally sized by TABLE 250/66 A normal grounding electrode for a structure is usually a ground rod serving a dwelling, or a metal water pipe in contact with the earth for at least 10’. ARTICLE 250/50/A If a water pipe is used then this metal water pipe must have a supplemental or auxiliary grounding electrode that is required to be associated with that metal water pipe. The supplemental grounding electrode is usually found to be a ground rod. ARTICLE 250/50/A/2 The grounding electrode conductor may be run from the ground electrode system to the fourth grounding lug of the meter base that is electrically joined to the grounded [neutral] conductor and to the metal frame of the meter base itself. ARTICLE 250/24/A/1 OR The grounding electrode conductor may be run from the grounding electrode system to the neutral / grounding combination bar or bars located in the main service rated panel or disconnect. ARTICLE 250/24/A/1 The grounding electrode system serving a dwelling is usually a ground rod, because most grounding electrodes listed in 250-50 are not available. You must land the grounding service conductor either in the meter base or main panel, BUT NOT BOTH. ARTICLE 250/142/A

It is advisable not to run a fourth conductor between the meter base and the main service panel, this would cause a paralleling affect not considered to be safe in the electrical field. A neutral service conductor carries the unbalanced load between the two hot conductors. If you ran a fourth bare grounding jumper between the meter base and the panel, and you happened to lose that larger, insulated, current carrying, neutral service conductor’s connection, then that little bare grounding jumper, installed parallel with that neutral and connected to the same places as that neutral, would try to take over the job of that larger insulated neutral. If this happens a bare, smaller, inadequate, conductor would suddenly be a current carrying conductor that has energized all metals exposed to people it is in contact with. This energized metal can provide a difference of potential to ground seeking an easier path to earth, probably, through your body. The neutral wire [white or gray service entrance conductor found between the meter base and the main panel is allowed to act as a duel purpose conductor, that is insulated and much larger. This neutral conductor [whiter or gray service entrance conductor] is allowed to serve as both the neutral and the equipment grounding path between the meter base and the main panel, regardless where you install the grounding electrode conductor coming from the grounding electrode system. ARTICLE 250/142/A and 250/24/A

The ground rod will most likely be the grounding electrode system for a dwelling because that will probably be the only grounding electrode available at the time of wiring that dwelling. However, If you have a metal water pipe that is in direct contact with the earth for at least 10’ then you must use this metal water pipe as the main grounding electrode, ARTICLE 250/50/A but you must also install a back up grounding electrode listed in ARTICLE250-50 or 52 [usually a ground rod] associated with that metal water pipe grounding electrode just in case someone removes that metal water pipe and install a plastic water pipe in its place. ARTICLE 250/50/A/2 If this replacement of a metal water pipe with a plastic water pipe would occur then your grounding electrode would have been removed and your dwelling would no longer have a grounding electrode system without the back up grounding electrode being present [usually a ground rod].

If a water pipe is available that is in direct contact with the earth for at least 10’ then the grounding electrode conductor connecting that water pipe grounding electrode to the main service panel or meter base must be connected within 5’ of the entry of the water pipe into the building.

The NEC says that IF AVAILABLE any of the following must be joined together to make the grounding electrode system for your structure. Your primary grounding electrode must be the water pipe if available and only if it is in direct contact with the earth the required 10’ then also a supplemental grounding electrode must be installed. ARTICLE 250/50/A The following are more grounding electrodes that you must use if available, the metal frame of a building or structure, any concrete encased electrodes [steel re-enforcing bars in concrete, etc.], a grounding ring [#2 copper found in footing of structure encircling the whole foundation that is at least 20’ long as a minimum length requirement but still encircling the entire foundation and at least 2 ½’ deep], and any made electrodes. [any metal underground structures even a metal frame of junk tractor, any underground tank, or any other metal pipes or rods such as ground rods. [If a rod or pipe, that rod or pipe must be at least ½” in diameter if made of ferrous metals, or at least ¾” diameter if iron or steel but iron or steel must be galvanized], any plate electrodes at least 2’ square in size and at least ¼” thick, and at least 2 ½’ deep. ARTICLE 250/54/C ALUMINUM GROUNDING ELECTRODES OR GROUNDING ELECTRODE CONDUCTORS MUST NOT BE USED IN DIRECT CONTACT WITH EARTH. ARTICLE 250/54/E AND ARTICLE 250/64/A

If a ground rod is the only grounding electrode available then that made grounding electrode [ground rod] will be your grounding electrode system. Remember that commonly most of the above mentioned grounding electrodes will not be available and / or be buried under the concrete, etc. before you get there. Therefore, none of those mentioned would be considered available to you. If available then all the above mentioned grounding electrodes must be bonded together as one entity thus forming your grounding electrode system as required. IF THEY ARE AVAILABLE DURING THE TIME OF YOUR WIRING INSTALLATIONS. ARTICLE 250/50

The grounding electrode conductor [that sole conductor between your grounding electrode and your service, no matter whether it is landed in the meter base or in the main panel or even at the weatherhead must not be broken. You must size the grounding electrode conductor meeting the requirements found in TABLE 250/66. The minimum size grounding electrode conductor for a 100 amp service in copper will be #8. The minimum size for a 200 amp service in copper will be #4 The maximum grounding electrode conductor can not be required to be larger than a #6 when serving a made electrode only [usually a ground rod] ARTICLE 250/66/A

Gas piping must not be used as a grounding source! ARTICLE 250/52/A

BONDING METAL WATER PIPES

If you do not use the water pipes as the primary grounding electrode, because there is no metal water pipe in direct contact with the earth at least 10’ in length, ARTICLE 250/50/A and if your water pipes are metal, then you must bond your metal water pipes to the grounding electrode system. ARTICLE 250/104/A This is required to make the water pipes one with the grounding electrode system the same as one entity. The purpose of bonding the metal water pipes to the grounding electrode system is so that if an energized wire comes in contact with those metal water pipes, a signal will go back to the panel that a short has occurred and the breaker serving or protecting that energized wire will trip due to a short circuit. This tripping of that breaker is due to the required interrupting rating of that breaker. ARTICLE 230/208

You must bond the metal water pipes, and any other metal piping system, ARTICLE 250/104 including the gas piping ARTICLE 250/104/B with the grounding electrode system of the structure. You must do this bonding of all metals of substantial quantities to make all metals one with the grounding electrode system serving that structure. The purpose of this bonding is to ensure that there is limited chance for a difference of potential between any metals in that structure, even the metal skin of a building. The intent is to make all metals one entity.

Metal gas piping systems must be bonded also, BUT MUST NOT USED AS A GROUNDING SOURCE, just made “one with the grounding electrode system of the building as one entity”. This bonding may be done by incidental connection at a gas appliance by the connection of the branch circuit equipment grounding conductor that is feeding power to that gas appliance. If you have a gas furnace and that gas furnace is fed by a 14 Ga. nonmetallic sheathed cable [Romex]. The 14 Ga. bare equipment grounding conductor found in that branch circuit nonmetallic sheathed cable [Romex] will meet the equipment grounding requirements of the gas piping system. ARTICLE 250/104/C

REMEMBER

YOU ARE NOT ALLOWED TO USE AN UNDERGROUND GAS PIPE AS YOUR GROUNDING SOURCE. ARTICLE 250/52/A

If you have substantially plastic plumbing or any other nonmetallic systems that have short pieces of metal associated with the plastic systems such as metal water pipes of short lengths, like between the plastic plumbing in the crawl but metal pipes up through the floor into the faucets at the sink, you can omit these short pieces as not substantial. These not substantial pieces of metals are not required to be bonded to the equipment grounding system.

An explanation concerning the requirements of bonding these metal systems that are not in substantial contact with earth but are a substantial mass of metal can be provided in “laymen’s terms” as follows; A gas piping system, metal heat duct, metal water pipes of substantial quantity may become energized by a bared hot conductor [ungrounded conductor] that has been damaged and laying across the metal gas piping, etc. This scenario will create a short to the metal gas pipe, metal water pipe, etc. that will energize that metal piping to full voltage. If the metal piping or any other metal component is not bonded to the structure’s electrical grounding system, a signal can not be sent to the over current device [breaker or fuse] telling that over current device that a short exists. This signal is required to go back to the over current device to tell that over current device to trip due to its interrupting rating when a short circuit appears. If the piping system is not bonded to the electrical grounding system the shorted, energized piping will remain energized waiting to spark, or shock anyone or anything coming in contact with that metal piping system that has a contact to earth. This danger will exist as long as eternity and without warning if that bonding to the electrical grounding system is not present making that metal piping system one with the equipment grounding system of the dwelling.

If you are wet and you happen to touch that energized metal piping system, you will not like the experience, that is IF you live to tell about it. Bonding the gas piping and isolated water piping, and metal ducts, etc. to the equipment grounding system of your dwelling’ service can eliminate the potential for shock or explosive ignition of a leaking gas pipe due to an electrical spark caused by this difference of potentiality.

This term signal telling the overcurrent device to trip due to the interrupting rating of that overcurrent device [breaker or fuse] is actually a large rush of current momentarily present on the equipment grounding conductor going back to the panel system. This signal I am speaking of is kind of a misconception but seems to help in laymen understanding the short circuit process.

You must size the equipment grounding conductors by using TABLE 250/122 The water piping systems must be connected to each other by connecting the nearest ¾ trade size water pipe of each system [hot and cold pipes] and then these must be connected to the main service panel ARTICLE 250/104, these attachments must be accessible. ARTICLE 250/104/A This bonding is intended only to make all metals in the structure as one entity, to keep the electrical system in contact with the associated metals found within a dwelling but are not normally used in the electrical system.

PROTECTING THE GROUNDING ELECTRODE CONDUCTOR

If you run the grounding electrode conductor within a wall and the outside and that grounding electrode is not likely to be exposed to severe physical damage, you are allowed not to protect that grounding electrode conductor further from physical damage. This is true only if you are running the grounding electrode conductor within the walls and only a short section is outside but protected from severe physical damage. Example would be the grounding electrode conductor hidden by the PVC conduit of a down pipe protecting your service lateral. [underground utility wire going to your meter].

If you run a conduit to protect the grounding electrode conductor running from the meter base to the earth located outside, then I suggest that you run only ½” PVC conduit down between the meter base and the earth to protect that grounding electrode conductor. You may connect the grounding electrode conductor to the made grounding electrode with a one piece acorn grounding clamp.

If you run a conduit to protect the grounding electrode conductor running from the meter base to the earth located outside, and you ran a metal conduit down between the meter base and the earth to protect that grounding electrode conductor. You must use a two piece ground clamp on the end of the metal conduit ARTICLE 250/64/E and ARTICLE 250/92 and then you may connect the grounding electrode conductor to the made grounding electrode with a one piece acorn grounding clamp. ARTICLE 250/92

You must not connect more than one grounding electrode conductor to a ground clamp. ARTICLE 250/70 You may install more than one acorn grounding clamp to one made grounding electrode if you like. You must not use a two piece ground clamp in trying to connect the metal conduit to the ground rod at the same time connecting the grounding electrode conductor to the made electrode [ground rod]. ARTICLE 250/70 and ARTICLE 110/3/B The conduit will mash and become damaged, causing a loose connection for both the grounding electrode conductor and the required metal conduit grounding procedure. The ground rod and the clamp must be found below the sod or dirt or protected from physical damage. The NEC no longer wants the ground rod and grounding electrode conductor above ground due to the connection being damaged or loosened by lawnmowers etc. striking that connection. Just dig a shovel full out before you start driving your ground rod and then drive the rod below the finished grade of the dirt, or protect that connection substantially. ARTICLE 250/52/C/3

This document is based on the 1999 national electrical code and is designed to give you an option, as a self-help, that should pass minimum code requirements. While extreme care has been implemented in the preparation of this self-help document, the author and/or providers of this document assumes no responsibility for errors or omissions, nor is any liability assumed from the use of the information, contained in this document, by the author and / or provider.

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