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

Definition of the Term "Ground" as Pertaining to the Electrical Construction Industry (NEC 1999)

By Warren Goodrich
Definition of the Term "Ground" as Pertaining to the Electrical Construction Industry (NEC 1999)

1 - RECEPTACLE STYLE AND TYPE

All receptacles on a temporary must be GFCI protected. ARTICLE 305/6/A and B If all receptacles on the temporary are on the same circuit, the GFCI mounted as the first receptacle on that circuit will protect all other receptacles on that circuit. The lead receptacle on each circuit must be a GFCI receptacle.

You may use a GFCI breaker on each circuit instead of the GFCI receptacle. Any 240 volt receptacles, or any 30 amp - 125/volt - twist lock style receptacle is also required to be GFCI protected. ARTICLE 305/6/B Any direct connect circuit {connectors & wire nut style connection} is allowed not to be GFCI protected, until a receptacle appears on that circuit, then the GFCI protection must appear when that receptacle appears. If the direct connect circuit is direct connected, at the end of line, without any receptacle on that circuit, then no GFCI is required. ARTICLE 305/6/A and B Code mute

If this temporary service pole is being used on a construction project during construction, and if you take the option of a direct connection without a receptacle, then you must utilize a GFCI receptacle upon the first appearance of any general use receptacle to protect personnel. ARTICLE 305/6/B

2 - RECEPTACLE BOX / STYLE AND TYPE

All boxes on a temporary, except special applications, will be considered exposed to wet location. Therefore all boxes, fittings, and covers must be approved as weatherproof. ARTICLE 373/2 The receptacles on the temporary must have a weathershield mounted over the box. ARTICLE 410/57/B This will look like a plastic cover you would find over a thermostat in a motel hallway, except the weathershield must be approved as weatherproof and approved for the purpose. This weathershield might be clear or opaque. If the box is metal, you must bond the metal box to the grounding conductor. ARTICLE 250/146 The bonding method may be accomplished by installing a green ground screw secured to a threaded hole in the back of the box. The bonding method may, also, be accomplished by installing a self grounding receptacle approved for the purpose.

You can identify a self-grounding receptacle by the spring clip mounted at the yoke, to insure an adequate contact to the box. ARTICLE 250-146 This type of self-grounding receptacle is commonly used on conduit style commercial project where no grounding conductor is ran, but using the conduit as the grounding path. ARTICLE 250-146-B The boxes must be securely mounted to the structure of the temporary. ARTICLE 300/11

3 - POLE DIMENSIONS / STYLE / TYPE / DEPTH REQUIREMENTS

The following requirements will not be found in the NEC but these requirements will most likely be required by either the Utility Company rules, or the Authority Having Jurisdiction. The Authority Having Jurisdiction will use the NEC articles referring to the requirement that any permanent wiring style must be substantially mounted to a permanently installed structure. You will find in the Chapter for temporary wiring that any service is not considered as temporary but must be referred to Article 230 for permanent service installations.

The pole on an underground temporary must be a minimum of 4" wide and 4" thick. The length requirement, generally is, approximately 10’ long.

"EXPLANATION" If you put 2’ 6” of post in the earth, run your downpipe up the post to set your meterbase at 3’ {to center}, above finish grade, then, mount your disconnect, or panel-taking up approximately 1’ 6”, and then, mount your receptacle box [or boxes]-taking up approximately 17” above that, you have used up approximately 8’ 5” of a 10’ pole. This leaves your pole approximately 7’ 6” above the finish grade and a total of 1” 6” of unused pole left over, to install 240 volt receptacles etc., if needed. A 10’ pole usually works out to "what is needed" for this design of underground temporary.

4 - NIPPLE STYLE AND TYPE
[BETWEEN DISCONNECT AND RECEPTACLES]

When you come out of the top of the disconnect with a weatherproof hub from the manufacturer of your panel, you will find your bossed receptacle box conduit hole, offset, from the hub at the top of your panel box. You can usually resolve this situation, by using an offset nipple. The minimum size , for a total number of conductors of three to nine 14 Ga. / or three to nine 12 Ga. THWN wires, which should be an adequate number for most applications from panel to receptacle paths, is 1/2". Chapter 9 Table 1 Note 4 You could use a 1/2" offset nipple. this offset nipple, will usually make your "existing offset condition" work out, by twisting the offset 1/4 turn, to lessen the depth of offset adjustment needed, in order to meet your receptacle box bossed hub from your panel box hub. The minimum size wire to your receptacles, through your offset nipple, from your over-current device [breaker or fuse], is 14 Ga. using a 15 amp maximum size overcurrent device. The maximum size wire to your convenience style receptacles, through your offset nipple, from your overcurrent device [breaker or fuse], is 12 Ga. using a 20 amp maximum size overcurrent device. The maximum wire size to a duplex receptacle is 12 Ga. on a 15 or 20 amp overcurrent device. A 15 amp receptacle is allowed to serve either a 14 Ga.-15-amp - and / or a 12 Ga.-20 amp branch circuit overcurrent device [fuse or breaker]. Any form of receptacle larger than a 20 rated receptacle must be a twist lock style, and weather proof. ARTICLE 305/6/A and B

Please keep in mind that any conductor # 4 or larger must be protected with plastic bushings. PVC is not exempt from the plastic bushing requirement. ARTICLE 300/4/F

5 - DISCONNECTS / SIZE / STYLES / TYPES / MINIMUM SIZES PER CIRCUITS

Your overcurrent device [breaker box or fuse box] can be of an array of sizes, each size creating new requirements. I will attempt to approach the majority of your choices.

If you use a type service panel limiting only one circuit in the box, you may use a minimum rating of 15 amps, weatherproof service rated panel. ARTICLE 230/79/A

If you use a type service panel with only two circuits in the box, you must use a minimum rating of 30 amps, weatherproof service rated panel. ARTICLE 230/79/B

If you use a type service panel with more than two [three or more] circuits in the box, you must use a minimum rating of 60 amps, weatherproof service rated panel. ARTICLE 230/79/D

You must use a service rated panel equal to or larger than the demand load calculated for your project as required by ARTICLE 220

Please keep in mind, that if you have six or less [breakers or disconnects] {that are grouped}, a main disconnect, and / or, breaker is not required as long as they are permanently secured to the service panel. ARTICLE 230/71

Please keep in mind, that if you use a single main overcurrent device smaller than the maximum rating of your service panel, you may reduce the feeder size to equal your main overcurrent device maximum rating, but you must provide the maximum demand load to the equipment to be used.

The main overcurrent device, must be locked in place in the panel, to be used as a main overcurrent device.

Please keep in mind, that although you are working with a "temporary", Article 230 must still apply as a permanent service, and be treated as such.

Please keep in mind that any equipment being utilized as a service panel must be service rated.

6 - NIPPLE / STYLE / TYPE [BETWEEN METER AND DISCONNECT]

Your nipple between the service panel, and the meterbase, must be sized by the feeder sizes which must be sized by the total of your service panel main over-current device/s maximum rating, or provide the maximum demand load of the equipment to be used on this service.

If your service panel main over-current device size is 30 amps [which must be locked in place if a breaker], you may use a feeder rated no less than a 30 amp rated conductor, from the transformer, through to the main lugs of the service panel, or the lug of your main over-current device.

If your service panel main over-current device size is 60 amps, [which must be locked in place if a breaker], you must use a feeder rated no less than a 60 amp rated conductor, from the transformer, through to the main lugs of the service panel, or the lug of your main over-current device.

If your service panel main over-current device size is 100 amps [which must be locked in place], you must use a feeder rated no less than a 100 amp rated conductor, from the transformer, through to the main lugs of the service panel, or the lug of your main over-current device.

If you use a "main lug only" panel, and you have only one circuit available in the service panel and the box is 15 amp rated you may use a feeder rated no less than a 15 amp rated conductor.

If you use a main lug only panel, and you have only two circuits available in the service panel and the box is 30 amp rated or less you must use a feeder rated no less than a 30 amp rated conductor.

If you use a main lug only panel, and/or you, have, three or more, circuits available in the service panel, and the box is 60 amp rated, or more, you must use a feeder rated no less than the maximum rating, of the service box over-current device, and / or, of the maximum rating of the service box itself, if the over-current device was not installed by the manufacturer, and / or, if the service box is a main lug only panel. This feeder may have to be rated, as much as, 200 amps, or more, depending on the maximum rating of the service panel over-current devices, and whether the main over-current device can be easily changed to a larger over-current device, or there is no over-current device in the service panel. NEC Table 310-16 and 230/42 and 240/6/D

7 - METERBASE / SUPPLIER / REQUIREMENTS

Some Utility companies will furnish that meter base for your temporary. Some Utility companies require you to furnish your meter base. You really should call your local Inspector and your local Utility company to confirm what rules apply in your area concerning that meter base. Also check with them concerning any special local rules applying to temporary services. Some Utility companies even will furnish the entire temporary and electricity for one set fee. This is where you really should make those two contacts both the AHJ and your serving Utility Company for specialized local rules.

8 - STRAPS / WHERE REQUIRED

You must support the downpipe with straps. The NEC states that you must install a strap near each end of the conduit.

9 - FEEDER / STYLE / TYPE / SIZE

If you are using this temporary on a residential application, you may size your feeders by 310/15/B/6

allowing a reduction in size. If you are using this temporary on a non-residential unit you must size your feeder by 310/16.

Special Note: Keep in mind that the charts must be adapted to meet the requirements of Article 110-14 . If the conductor is smaller than a #1 AWG. then the temperature rating of the conductor as per the ampacity in Article 310/16 must be limited to 60 degree centigrade [such as the column for TW conductors] regardless if the conductor is rated 75 or 90 degree such as THHN Conductors. If the conductors are used as a feeder for a residential setting then you may disregard the temperature limitations and use the Table 310-15-B-6 exclusively. This use of Table 310-15-B-6 may be controversial when used on a residential setting yet on a temporary. Please contact you local AHJ to confirm that you are allowed to use this table in your local area.

In this application you must use a conductor approved for a wet location ,and approved as a service conductor [with a "U" in it's identification]. If you plan to run a conduit non-stop from the meterbase, into the earth and then to the transformer, running the conduit all of the way from the meterbase to the transformer you may run type THW or THWN or XHHW. These conductors are required to be protected. [in a conduit] If you plan to use a feeder without the protection of a conduit all of the way to the transformer while underground, you must use a conductor approved for direct burial. This direct buried wire must contain a "U" in its identification to signify approval for a direct buried, underground application. An example of an underground feeder approved for direct burial and approved as a service conductor would be type URD if aluminum or USE if copper. Table 310-13

The following feeders are accepted practice to use in this application to serve as a feeder to a residential temporary, but this list does not name all conductors approved for this application.

COPPER FEEDERS

30 amp rated direct buried = 10 Ga. UF

30 amp rated contained within a conduit = 10 Ga. THWN / OR / THW / OR / XHHW

60 amp rated direct buried = 4 Ga. USE

60 amp rated contained within a conduit = 4 Ga. THWN / OR / THW / OR XHHW

100 amp rated direct buried = 4 Ga. USE

100 amp rated contained within a conduit = 4 Ga. THWN / OR / THW / OR XHHW

200 amp rated direct buried = 2/0 USE

200 amp rated contained within a conduit = 2/0 THWN / OR / THW / OR XHHW

ALUMINUM FEEDERS

30 amp rated direct buried = 8 Ga. URD OR LARGER IF NOT AVAILABLE

30 amp rated contained within a conduit = 8 Ga. THWN / OR / THW / OR / XHHW

60 amp rated direct buried = 3 Ga. URD OR LARGER IF NOT AVAILABLE

60 amp rated contained within a conduit = 3 Ga. THWN / OR / THW / OR XHHW

100 amp rated direct buried = 2 Ga. URD

100 amp rated contained within a conduit = 2 Ga. THWN / OR / THW / OR XHHW

200 amp rated direct buried = 4/0 USE

200 amp rated contained within a conduit = 4/0 THWN / OR / THW / OR XHHW

Special note: If you are using aluminum wiring you must use anti-oxidation inhibitor [Nolox].

Special note: Your feeder must be long enough to reach the transformer plus at least 10', if you consider the feeders being cut off at each job site the 10' extra won't last long.

10 - DOWN PIPE / TYPE / STYLE / MINIMUM SIZES

Accepted practice will lead you to Sch 80 PVC due to a cost factor.

You may use rigid or intermediate style conduit also. You must not use EMT in direct contact with the earth.

Due to the direct burial requirement [conduit is required to end a minimum of 18" below earth entry] and subject to physical damage, flex must not be used. flex is not approved for direct burial or where subject to physical damage. [ bush hogs, etc.]

Due to being subject to physical damage Sealtite must not be used. [bush hogs, etc.]

Due to being subject to physical damage Sch 40 PVC must not be used. [bush hogs, etc.]

Please keep in mind that any conduit with # 4 Ga. or larger conductor must be protected with plastic bushings. PVC is not exempt from the plastic bushing requirement.

11 - TRANSFORMER

Your Utility Company will flag the area where they plan to set your transformer, and your Utility Company will furnish your transformer for you.

12 - GROUNDING REQUIREMENTS

You must drive a 1/2" x 8' minimum size made grounding electrode [Ground rod] at your temporary.

You must then run the grounding service conductor up the pole to the service panel. Article 250/52/C/2

You must not use an aluminum grounding electrode in direct contact with the earth. Article 250/52

You must not use an aluminum conductors as a grounding service conductor in direct contact with the earth. Article 250/64/A

Absolute minimum grounding service conductor is a # 8 copper for 100 amp or less and # 6 copper for more than 100 amp. Article 250/66

Grounding service conductor sizes between a ground rod and a service panel are as follows;

30 amp feeder = # 8 copper grounding service conductor Article 250/66

60 amp feeder = # 8 copper grounding service conductor Article 250/66

100 amp feeder = # 8 copper grounding service conductor Article 250/66

200 amp feeder = # 6 copper grounding service conductor to a made electrode. [ground rod] Article 250/66/A

13 - GENERAL INFO ON TEMPORARY APPROVED LENGTH OF TIME TO BE USED

The maximum allowable time for any type of temporary wiring are as follows; 90 DAYS on non construction type projects. Article 305/3/B

LIFE OF CONSTRUCTION PROJECT where on a construction site as long as construction process is an active construction project. Article 305/3/A

Special Note: The temporary wiring style running from the temporary on the load side of the overcurrent device is rather forgiving on a temporary wiring condition. You must show that the temporary wiring is under a controlled supervision. [ NOT SERVICE EQUIPMENT ]

Special Note Braces are not required on an underground style Temporary

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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