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HVAC and Refrigeration Nameplate Data (NEC 2002)

By Warren Goodrich
HVAC and Refrigeration Nameplate Data (NEC 2002)

This article is intended to advance the general understanding of HVAC and refrigeration name plate data.

Definitions and Explanations

HVAC: Heating, ventilating, and air conditioning; designed to maintain comfort, or sustained ambient temperature.

Refrigeration: Cooling and freezing units designed for food storage.

Code information regarding hermetic compressors is found in the NEC article 440.

Compressor data company nameplate example:

Model X VAC HZ PH RLA LRA FLA
Compressor 230 50 1 20.6 95 ---
Outdoor Fan Motor 1/2 hp 230 60 1 --- --- 1.2
Branch Circuit Selection Current 34.3 amps 60 1 --- --- 1.2
Minimum Circuit Ampacity 27 amps
Maximum Fuse or HACR Type Breaker 45 amps
Operating Voltage Range: 197 min 253 max

The Difference Between a Normal Motor and a Hermetic Motor

  • A hermetic motor compressor combines motor and compressor into one complete unit with the refrigerant contained internally to the compressor
  • A normal motor and compressor unit is a separated cooling unit with a drive connection between the motor, and the compressor--belt driven or direct drive shaft style, etc.
  • A hermetic compressor has no shafts used in its design
  • A motor and compressor separated unit will have a shaft or belt tying the separated motor to the external compressor unit
  • A hermetic motor compressor operates with the refrigerant being a part of the motor's operation
  • A separated motor and compressor unit are separate components that will normally use an air cooled standard electrical motor much like any normal motor being used to drive any other type machinery
  • A hermetic compressor is not measured in horsepower like a normal motor is measured
  • A hermetic compressor's amp draw of electricity changes with the back pressure changing that is developed by the compressor and the flow of refrigerant

Standard electric motor FLC [full load current] are found in the NEC tables 430-148, and 430-150.

In the motor and compressor separated unit the motor does have a rating in horsepower or FLC [full load current] {amp rating of motor when a full load is applied to the motor for work being done}. Again this FLC rating for each normal horse power rated motor is found in Table 430-148 or table 430-150 of the NEC.

Hermetic Compressor

A hermetic compressor unit works as follows; as the compressor builds up pressure, the current increases, causing the windings to get hot, but at the same time, the cooling refrigerant, passes around the heated windings. This cools the motor windings. Considering the operation of this motor you will not find the presence of resistance due to friction of a motor shaft because there is no shafts in this hermetic compressor. Because of this lack of friction and the heating of the windings and the coolant hitting the heated windings cooling them, the hermetic compressor can be worked much harder than a normal standard horse power style motor of the same relevant size and strength. This ability to work a hermetic compressor much harder is because it is cooled by submersion in the coolant contained within and does not rely to much extent in its design on air for cooling the compressor to prevent overheating normally found with the use of a normal electric motor. This ability to perform harder work of a hermetic compressor can be loosely explained if we thought of the principle that heat seeks cold. While thinking of the heat seeks cold principle, then you might say the hermetic compressor operates on the heat seeks cold principle using that method of cooling to be able to produce more work from the hermetic compressor by moving or pumping the refrigerant that produces the cooling activity we are wanting to be produced from our equipment.

Horse Power Rated Motor and Separated Compressor Unit

A normal horse power rated motor and separated Compressor unit works as follows. As the separately installed belt or shaft driven compressor builds up back pressure, the motor current increases due to the increased motor load applied. This causes more resistance against the motor's ability to turn freely. This increased resistance causes the amps of the standard electric motor to increase thus causing the windings to get hot due to the limitations of the air cooling capabilities concerning the convection of the heat away from that standard air cooled motor. The heat also increases on the separated compressor due to friction of the compressor much like the compressor of a normal air compressor heats up with use, much as the air pressure increases against the pumping action of the normal air compressor. This air cooling by convection or fan in the standard electric motor housing can not be compared in efficiency or ability to perform work compared to the internal cooling capability of a hermetic compressor using the coolant to cool the hermetic compressor. A separated cooling compressor unit operates much like the compressor of that air tank compressor with some water pump principles also involved in its design. This separated cooling compressor actually pumps the coolant through the lines causing the vaporizing to gases of the coolant thus causing the “A”coil to get cold. The coolant being pumped by a separated belt driven cooling compressor going back to the compressor has turned back into liquid once it has cooled the “A”coil but is not acting as a coolant for the standard electric motor at the time it passes through this compressor pump type separated belt or shaft driven compressor. The pumping action of a belt or shaft driven compressor is driven by the separate electric motor and does not rely on the heat seeks cold principles to cool the standard electrical motor except by air convection to the atmosphere around it the coolant of the cooling system has no cooling effect concerning that standard electric motor.

This less adequate heat dissipation capability of a standard air cooled electric motor driving a separate cooling compressor that also has air cooling type fins on this separately driven cooling compressor is less efficient. This heat build up and lack of cooling capabilities of a separated electric motor driven compressor unit has to be considered in the separated motor and compressor unit design requiring stronger equipment. This different excess heating and friction of the separated cooling compressor requires a stronger electric motor to compensate for the build up of pressure and friction resistance in the separated cooling compressor and electric motor driving that compressor. The increase in the motor sizing of a standard electric motor, compared to a hermetic compressor in order to perform the same amount of work as a smaller hermetic compressor, is required due to the lack of the ability of using the liquid cooling refrigerant to cool the standard electric motor compared to the method of work production of a hermetic cooling compressor this is due to the fact that this hermetic compressor contains liquid coolant passing through it carrying the heat away from the hermetic compressor thus working as a coolant in the cooling activity of the hermetic compressor. In the hermetic compressor the coolant is used to help cool the hermetic compressor and to lubricate that compressor at the same time that compressor is working to cause that coolant to remove heat from a designated area such as a home or freezer, etc through the use of an “A”coil and the vaporized coolant. The separated cooling compressor does not have the advantage of using the liquid coolant it is pumping to help cool and lubricate the separated motor driven compressor that is air cooled also pumping that vaporized coolant through the “A”coil.

Detailed Information Pertaining To:

  • Each area of a cooling unit nameplate
  • In short form answers
  • Minimums and maximums allowed or required wiring design serving an air conditioner unit matching the name plate below

Compressor Data Company Nameplate

MODEL Y VAC HZ PH RLA LRA FLA
Compressor 230 50 1 20.6 95 ---
Outdoor Fan Motor 1/2 hp 230 60 1 --- --- 1.2
Branch Circuit Selection Current 34.3 amperes
Minimum Circuit Ampacity 27.0 amperes
Maximum Fuse or HACR type Breaker 45 amperes
Operating Voltage Range 197 min. 253 max.

Using the above name plate of an air conditioner unit the following is required and allowed as minimums and maximums in the wiring design serving electricity to that air conditioner unit.

The overload protection will be found installed by the manufacturer either inside the component such as the hermetic compressor or fan motor, or this overload protection device will be found inside the air conditioner or refrigeration unit again installed by the manufacturer.

The branch circuit conductor size can be sized as a minimum circuit conductor size by using the MCA [minimum circuit ampacity].This name plate says the ampacity must equal or exceed 27 amps. Look in Table 310-16 in the 60 degree column as required in 110-14 for conductors smaller than a 1 awg conductor regardless of the insulation on that conductor. The minimum branch circuit conductor size for this name plate is 10 awg copper branch circuit conductor size.

Branch Circuit Conductor Size

The branch circuit conductor size should be sized in your best interest by using the BCSC [branch circuit selection current]. This name plate says the branch circuit selection current rating in amps is 34.3 amps. Therefore you really should size you branch circuit conductor size to equal or exceed that 34.3 amp value. Looking at Table 310-16 and considering the requirements of 110-14 you really should size your branch circuit conductor size as an 8 awg copper branch circuit conductor size. The extra cost of initial installation of the larger size branch circuit conductor will easily be offset in savings concerning the cost of electricity as you use the product.

Over-Current Protection

The maximum over-current protection is determined by the manufacturer and is usually found marked “maximum fuse or HACR type breaker”This data is found on the name plate, shown in the illustrated name plate as 45 amps, which is also a standard breaker size per 240-6.If the maximum fuse or HACR type breaker size in amps [maximum overcurrent protection] is not found on the nameplate, it may be determined as follows; RLA OR BCSC whichever is greater x 175%] or if that overcurrent device size won't carry the load without tripping then you may calculate as a maximum [RLA x 225%] but only if required for the equipment to work reliably without the overcurrent device tripping. See Article 440-22 This breaker or fuse is used only for short circuit protection. The overloads built into each component of that equipment is designed to protect the branch circuit conductor and / or component part such as the compressor itself. 20.6 x 225% would equal maximum overcurrent device [inverse time breaker] size of 46.3 amps then referring to Article 240.6 for a branch circuit allowing the next higher overcurrent device a 50 amp breaker may be used. This is only true if the"MAXIMUM FUSE OR HACRtype BREAKER is not present.

The minimum disconnect or controller rating would be sized by using the LRA [locked rotor amps]. The name plate above say 95 amps. You must then go to Table 430-152-A for a single phase motor then look for the voltage rating on your name plate above where it says 230 volts and you should find that a 95 amp rated disconnect or controller would be sized at a minimum of 3 horse power rated disconnect.

SPECIAL NOTE: Notice that we sized the electrical equipment by using the name plate above and installed a 3 horse power rated disconnect using a maximum amp rating of a 45 amp HACR breaker installed serving a 10 awg copper branch circuit conductor. This may seem wild or ludicrous but hang in there and read the details how we come up with that 45 amp breaker on a 10 awg 30 amp rated copper conductor. May be interesting.

Detailed Information Pertaining to Each Area of a Cooling Unit Nameplate

RLA = Rated load current explanations

Compressor data company nameplate

MODEL Z VAC HZ PH RLA LRA FLA
Compressor 230 50 1 20.6 95 ---
Outdoor Fan Motor 1/2 hp 230 60 1 --- --- 1.2
Branch Circuit Selection Current 34.3 amperes
Minimum Circuit Ampacity 27.0 amperes
Maximum Fuse or HACR type Breaker 45 amperes
Operating Voltage Range 197 min. 253 max.

Rated Load Current

Rated load current [RLA or RLC] of a hermetic cooling compressor; is calculated by calculating the product of 64.1% of the maximum load current [MCC], and is set and marked on the name plate as [RLA], by the manufacturer. You might want to think of [RLA] like the engine of your personal car. Although the speedometer on the dash might be marked with speeds up to 150 miles per hour with the engine being capable of going that fast at a maximum load, you would be better off if you decided to drive 96 miles per hour [64.1%], this being a nice comfortable maintained speed that would be an easy load on your car's engine, thus prolonging the engines life expectancy. If you notice, most normally used cars for, personal use, tend to have a life expectancy to be able to run for 100,000 miles or much more. Yet in the Indianapolis 500 race, on memorial day, the engine in that car is pushing the maximum limits of speed concerning that racing motor, pushing the maximum capability of that motor. This pushing the capabilities of that racing motor to its limits in load causes the designer of that racing motor to just have hope that it will last the entire 500 miles of that race. The idea of this racing engine, that is pushing its load limits to the maximum, having a life expectancy as long as a personal car lasting 100,000 miles or more would be beyond possibility due to the pushing of that racing motor's limits in work or speed. This is the idea of a comfortable maintained load or speed that I am trying to make a picture in your mind for you to see concerning the RLA or RLC. Check the NEC section 440-2 concerning this subject.

LRA = locked rotor amperes explanations

Compressor data company nameplate

MODEL A VAC HZ PH RLA LRA FLA
Compressor 230 50 1 20.6 95 ---
Outdoor Fan Motor 1/2 hp 230 60 1 --- --- 1.2
Branch Circuit Selection Current 34.3 amperes
Minimum Circuit Ampacity 27.0 amperes
Maximum Fuse or HACR type Breaker 45 amperes
Operating Voltage Range 197 min. 253 max.

Locked Rotor Amperes

Locked rotor amperes [LRA]; is the maximum current draw when the motor is in a locked position. This is when the rotor is locked and it is not capable for it to operate at all because the rotor is locked and unable to move. You must use this data to make sure that the interrupting rating capabilities of the disconnecting means and controller are adequate to carry the amps that may be demanded of it by this hermetic compressor carrying the name plate you are reading. See the NEC Articles 440-12 and 440-41.

In order to calculate the LRA of a hermetic compressor if the LRA is not on the name plate, you would have to compare that hermetic compressor with a standard electric motor. According to Article 430-148, the full load ampere rating of a 230 volt, single phase, 5 horse power standard air cooled electric motor is 28 amperes. In our example of a name plate seen above, the name plate rating of the RLA is 20.6 amperes. Therefore in order to select a disconnect switch approved for this load that being applied on this hermetic compressor, we must consider this hermetic motor unit to be equal to a 4 horsepower standard electric motor. In table 430-148 you should find a 3 horse power standard electric motor [FLC] full load current is rated at 17 amps. Comparing the 28 amps FLC rating of a 5 horse power standard electric motor and the 17 amps FLC rating of the 3 horse power standard electric motor. Then collating between the 3 horse power and the 5 horse power standard electric motor rating by subtracting the 17 amps FLC of the 3 horse power standard electric motor from the 28 amps FLC of the 5 horse power standard electric motor, you would find the difference between the two FLC amp ratings of the two standard electric motors that are listed in table 430-148 of the NEC. By dividing that difference of the two FLC amp ratings by two, that division calculated answer would give you the FLC [full load current] rating of a 4 horse power standard electric motor that has not been listed in table 430-148 of the NEC. This 4 horse power motor being rated in FLC is halfway between the 3 horse power and the 5 horse power standard electric motors found by collating the FLC of the 3 horse power and the 5 horse power motors to find the FLC of a 4 horse power motor. The answer would give us a 22.5 FLC rating for a 4 horse power motor. We have to do this collating calculation because The charts in 430-148 and 430-150 providing us with the FLC ratings of motors lists only the 3 horse power motor and the 5 horse power motor. The 4 horse power motor is not listed so we have to collate between the 3 horse power motor and the 5 horse power motor to find the 4 horse power standard electric motor full load current [FLC].

This hermetic compressor's rated load amps [RLA] rating on its name plate example above is 20.6 amps. 20.6 amps is closer to the 22.5 amp rating of a 4 horse power rated standard electric motor than the 3 horse power rated standard electric motor rated at 17 amp FLC. Therefore we would consider this hermetic compressor listed in the example name plate above to be rated as a 4 horse power rated hermetic compressor.

This is all true yet in sizing the disconnect by using table 430-151 in the NEC to find the minimum amp or horse power rating of your disconnect, your only choices are 3 horse power standard electric motor or a 5 horse power standard electric motor. We then must compare the FLC ratings of the 3 and 5 horse power rated standard electric motors to see which one would be closest to the RLA of the hermetic compressor of 20.6 amps. We should find that the RLA is closest to the 3 horse power rating in Table 430-151-A. Then we must use the 3 horse power rating found in table 430-151-A to size our hermetic compressor's disconnect or controller with the example name plate above.

Checking Table 430-151-A, the locked rotor current for a 230 volt single phase, 3 horsepower standard electric motor is 102 amperes, and the locked rotor current for a 230 volt, single phase 5 horse power standard electric motor is 168 amperes. Therefore in selecting a disconnect switch on the basis of locked rotor current [amperes], we should consider this hermetic compressor to be a 4 horse power unit as explained above. Checking manufacturer's literature on the disconnect switches ratings, you will find a 102 amp rated disconnect and 4 horse power rated will meet the NEC minimum safety requirements of the hermetic compressor that we have been working with using the example name plate above without having the manufacturer's LRA rating on their name plate. Note that this calculations of a LRA sizing the minimum amp and horse power rating of a disconnect device does not relate to the overcurrent device rating [breaker or fuse]. The above section concerning the LRA is only pertaining to minimum ratings of the disconnect switch itself if the LRA is not provided by the manufacturer. If the manufacturer provides the locked rotor amps [LRA] on their name plate then you use that value provided by them as the LRA to size your hermetic compressor by going to Table 430-151-A and finding the horse power rating of the disconnect required that meets the manufacturer's LRA rating provided on their hermetic compressor name plate. If the manufacturer does not provide the LRA then use the method of calculation provided in this section.

MCC = Maximum continuous current explanations

Compressor data company nameplate

MODEL B VAC HZ PH RLA LRA FLA
Compressor 230 50 1 20.6 95 ---
Outdoor Fan Motor 1/2 hp 230 60 1 --- --- 1.2
Branch Circuit Selection Current 34.3 amperes
Minimum Circuit Ampacity 27.0 amperes MCC
Maximum Fuse or HACR type Breaker 45 amperes NOT AVAILABLE
Operating Voltage Range 197 min. 253 max.

Maximum Continuous Current (MCC)

This is the maximum current that the hermetic compressor can draw before damage may occur to the compressor. The manufacturer of the hermetic compressor is expected to know the maximum load capable of that hermetic compressor that can be applied before damage will appear in their certain hermetic compressor. The manufacturer is supposed to provide the necessary internal over-current protection ratings on their name plate that should keep the hermetic compressor from causing damage to itself. This value is 156% of the RLA. This MCC concerns a single hermetic compressor without any other component loads applied.

Don't look for the MCC data on the nameplate of an air conditioning unit itself with the component loads applied, but only on the hermetic compressor by itself. This MCC rating of that single hermetic compressor would not apply to the maximum rating of the entire combined loads of all component motors installed making that air conditioner unit as a whole. Your air conditioner will also have a fan that also can draw a pretty heavy amp load of current. The two motors combined [hermetic compressor and fan motor] of an air conditioner would be a combined hermetic and standard fan motor component load. The two combined component loads would not be considered as just a single hermetic load.

You will probably not find this maximum current [MCC] rating anywhere on that nameplate of the air conditioner unit with all component loads combined. The MCC rating is only concerning the hermetic compressor by itself. If you do find the MCC rating on the actual hermitic compressor unit by itself within the air conditioner, do not use that information concerning an air conditioner as a complete unit due to the combined loads applied in that air conditioner. The manufacturer of the single hermetic compressor used as one of several components of this air conditioner unit furnishes this MCC information to the manufacturer of the air conditioner unit as a whole design during the making of the air conditioner unit considering the hermetic compressor as a component of their air conditioner during their designs for manufacturing only. Then the proper maximum overcurrent device ratings in amps information of that complete [combined components] air conditioner unit that you are supposed to use is then included and provided on the completed air conditioner unit's name plate. Do not use the single hermetic compressor component name plate when supplying power to a completely manufactured air conditioner unit that is using several different components like the hermetic compressor and fan motor to make up the completed air conditioner unit. Remember that these type of pieces of equipment are of a combined design and loads of different type motors from possibly different manufacturers being used to make a combined product of this air conditioner unit manufactured by yet a different manufacturer that has built the combined air conditioner unit. Only the manufacturer of the finished combined product using the combination of different types and sizes of motors in its manufacturing process would use the name plate information included on a certain component motor of a completed manufactured air conditioner unit. This is true whether this air conditioner unit is a window style or a central whole house style air conditioner unit. See NEC article 440-52. This single component being the compressor is a hermetic compressor and it will have an internal overload protection protecting that certain hermetic compressor alone and separate from any other loads in that manufactured air conditioner unit.

BCSC = Branch-circuit selection current

Compressor data company nameplate

MODEL ??? VAC HZ PH RLA LRA FLA
Compressor 230 50 1 20.6 95 ---
Outdoor Fan Motor 1/2 hp 230 60 1 --- --- 1.2
Branch Circuit Selection Current 34.3 amperes
Minimum Circuit Ampacity 27.0 amperes
Maximum Fuse or HACR type Breaker 45 amperes
Operating Voltage Range 197 min. 253 max.

Branch-Circuit Selection Current (BCSC)

The manufacturer of the cooling equipment might design better cooling and better heat dissipation into each unit. Thus, the hermetic compressor can be continuously worked harder than equipment not so designed. Examples such as a standard motor; Working the hermetic compressor harder will result in a higher current draw. This is safe insofar as the hermetic compressor is concerned due to the interior of the hermetic compressor being submerged in its on coolant fluids. In our example name plate above, the BCSC is 34.3 amperes. This branch circuit selection current on the name plate should be considered in sizing the branch circuit of this hermetic compressor, providing better safety and more efficiency concerning electrical usage and running cost. There will be an increase of cost of this larger than minimum allowed branch circuit conductor required by the NEC to serve this hermetic compressor. The savings of electric costs and extra safety made available by the larger branch circuit conductor installed by sizing the conductor using the BCSC on the nameplate rather than sizing the branch circuit conductor's minimum size allowed, would quickly absorb the initial increase in installation cost, if the large branch circuit conductor is installed. Then after you have saved enough money needed for you to be reimbursed for the added extra initial cost for the larger than minimum branch circuit size required, you would then be able to experience that savings in running cost of electricity for the life of the cooling equipment that the larger branch circuit conductor serves.

In my opinion the added safety and the added savings of the running cost of electricity produced by using the BCSC to size your branch circuit conductor instead of using the minimum allowed by the minimum circuit ampacity [MCA] would be a no brain-er.

MCA = Minimum circuit ampacity explanations

Compressor data company nameplate

MODEL C VAC HZ PH RLA LRA FLA
Compressor 230 50 1 20.6 95 ---
Outdoor Fan Motor 1/2 hp 230 60 1 --- --- 1.2
Branch Circuit Selection Current 34.3 amperes
Minimum Circuit Ampacity 27.0 amperes
Maximum Fuse or HACR type Breaker 45 amperes
Operating Voltage Range 197 min. 253 max.

Minimum Circuit Ampacity (MCA)

This is the minimum branch circuit ampacity requirement to determine the minimum branch circuit conductor size, and the switch rating. MCA data is found on the name plate telling us what the minimum ampacity allowed sizing the branch circuit conductor by Table 310-16 concerning your type of conductor and type of insulation of that conductor. This MCA listed on the nameplate is determined by the manufacturer as follows; [RLA x 1.25] + all connected loads or full load current of all other loads in that unit carried on that branch circuit. In our example of the name plate above, the name plate reads that the minimum circuit ampacity is 27 amps. The minimum branch circuit conductor then would be sized by meeting or exceeding the MCA on the name plate and comparing that ampacity requirement to the ampacity of conductors in the NEC Table 310-16. This would be the required ampacity of the branch circuit conductor serving that hermetic compressor and other loads in that unit and carried on that branch circuit conductor. The other loads would be a fan of a central air conditioner or heat pump built into the same unit as components of that unit. If there are no other loads then the MCA would be just the hermetic compressor load. See the NEC article 44-33 and 440-35 and 440-4-B.

SPECIAL NOTE;

You might want to notice that the sizing of the minimum circuit conductor ampacity requirement MCA on the name plate also matches the same way you would calculate the ampacity requirement sizing the minimum branch circuit conductor's ampacity rating of a standard electric motor as required in 430-22 for a single motor and 430-24 for more than one motor or connected load that carried on a single conductor. These article would be used if sizing conductors for standard electrical motors and other load concerning the NEC requirements for wiring designs of standard electric motors.

Concerning standard electrical motors, you would go to the NEC table 430-148 or table 430-150 to find the full load current rating of that standard electric motor. Then you would follow the rule in the NEC article 430-22 concerning the minimum branch circuit conductor ampacity rating by multiplying that FLC rating of the standard electric motor times the same 125% as you use in the calculation of the hermetic compressor branch circuit conductor ampacity. Then you would use 430-24 by multiplying the largest FLC of the largest motor load then adding the FLC and connected load amps of all other loads on that one conductor.

This example kind of shows that the two types of motors [standard electrical motor compared to hermetic compressor designs] are similar yet somewhat different in their running science. Just thought that I would add this in for your information in an attempt to show some logic to what is being said concerning hermetic compressors design.

Personal Advice

The following is a good sense statement not an NEC requirement concerning the minimum safety standards. Always use branch circuit selection current [BCSC] value when your are sizing your branch circuit conductor size instead of the minimum circuit ampacity [MCA] value. See NEC article 440-2 and 440-4-C of the NEC for selection of the size of branch circuit conductor that you should use.

Also only if the LRA is not shown on the name plate that you normally should use to size your disconnect or controller, then use the rated load amps [RLC or RLA] and perform the calculations using table 430-151-A or B for selection of the disconnecting means or controller.

MOP = Maximum Overcurrent Protection

Compressor data company nameplate

MODEL ??? VAC HZ PH RLA LRA FLA
Compressor 230 50 1 20.6 95 ---
Outdoor Fan Motor 1/2 hp 230 60 1 --- --- 1.2
Branch Circuit Selection Current 34.3 amperes
Minimum Circuit Ampacity 27.0 amperes
Maximum Fuse or HACR type Breaker 45 amperes
Operating Voltage Range 197 min. 253 max.

Maximum Overcurrent Protection [MOP]

See maximum fuse or HACR type breaker in the name plate example above.

The maximum over-current protection is determined by the manufacturer and is usually found marked “maximum fuse or HACR type breaker” This data is found on the name plate. If the maximum fuse or HACR type breaker size in amps [maximum overcurrent protection] is not found on the nameplate, it may be determined as follows; RLA OR BCSC whichever is greater x 175%] or if that overcurrent device size won't carry the load without tripping then you may calculate as a maximum [RLA x 225%] but only if required for the equipment to work reliably without the overcurrent device tripping. See Article 440-22 This breaker or fuse is used only for short circuit protection. The overloads built into each component of that equipment is designed to protect the branch circuit conductor and / or component part such as the compressor itself.

A typical nameplate will show the maximum size overcurrent device required [maximum HACR breaker or time delay fuse]. If fuses are specified only and HACR breakers are not listed or mentioned the circuit breakers are not permitted to be used on that certain machine that does not have mention of HACR breakers on their name plate. Often times inverse time breakers can not handle the in-rush of current caused by the start-up load of a certain machine or hermetic compressor.

In our example above of a nameplate, the nameplate indicates HACR. The HACR stands for “heating, air conditioning, refrigeration”. Most molded case circuit breakers today are marked and listed as HACR breakers.

Watch out when connecting HVAC {heating, ventilating, air conditioning} or refrigeration equipment to existing electrical panel boards where the HACR marking might not be found on the breakers designed for that older panel board. A simple way to know if the installation meets the NEC minimum safety standards is to make sure that the HACR marking appears on the cooling unit's nameplate, and on the breaker's labeling. See NEC article 440-22.

SPECIAL NOTE: Seeing the similarity of the standard motor design and the hermetic compressor design requirements; Again you should be able to compare the maximum overcurrent device rating allowed in the standard motor design matching the same calculations used in the hermetic compressor designs. In designing a standard motor wiring system you would again go to the NEC table 430-148 to find the full load current [FLC] rating of that standard electric motor and then go to the NEC table 430-152 to find the maximum overcurrent protection amp rating. The same 2.25 multiplication times that FLC [full load current] rating would find your maximum inverse times breaker [normal breaker that you would use in a building.] Remember in both the hermetic compressor and the standard motor design requirements the overcurrent device is not what is designed to protect the conductor or windings of a motor from damage due to overheating. In both the hermetic compressor and the standard electric motor must meet the minimum overload size required and be below the maximum overload size allowed. Hermetic compressors and single phase standard electrical motors single phase normally have overload protection built into these motors by the manufacturer, in the form of a thermal cutout. Built in overloads [often a thermal cutout protective device built into the motor] can be automatically reset or operated manually be a red reset button. Three phase motors are still required the same overload protection yet is usually installed by the electrician in a separate motor control center. The overload is the branch circuit conductor's and motor winding's protection from damage due to overworking or overheating [overloading]. These two subjects both hermetic compressors and standard electric motors are the “when otherwise allowed or mentioned”as referred to in the NEC. Chapter 4 of the NEC which includes both article 430 standard electric motors and article 440 hermetic compressors is that “when otherwise allowed or mentioned in the NEC”. The designs and even conductor ampacity in the NEC table 310-16 changes allowing different from the normally accepted in Chapters 1 through 3 of the NEC. Chapter 4 of the NEC is a different world in the NEC allowing or requiring much different electrical designs than is normally accepted in standard wiring methods found in Chapters 1 through 3 where you must have the branch circuit protective device [branch circuit fuse or breaker] on the beginning [line side] where the branch circuit gets its power from. When you are dealing with motors of almost all kinds the motor's overload device is the device that protects that branch circuit serving a motor. This overload device is most often found or installed at the end of a branch circuit conductor at or in the motor itself. Seems like the rules tend to reverse from what is required concerning motors compared to all other types of wiring designs.

The difference is the breaker or fuse is serving a motor is often times just a short circuit protection device only. The breaker or fuse is commonly serving to trip due to its interrupting rating due to short circuits only. The overloading or overheating of branch circuit conductors or windings of the motors are expected to be protected by the “overload device”

There are some exceptions allowing a certain “time delay type fuse”that has been sized within the minimum and the maximum overload protection sizes as required”to serve as both the branch circuit interrupting device protecting for short circuit and the overload device protecting the motor branch circuit conductor and the motor windings. Kind of what you would call a dual purpose device serving both requirements. Remember that time delay style fuses are the only type of fuse allowed to act as an overload device protecting a motor windings or branch circuit conductor serving a motor. NO breaker or no-time delay type fuse is allowed to serve as an overload device protecting a motor unless that motor is smaller than 1 horse power that is not automatically controlled.

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