maximum amps

[mdoolittle]

Working on an electrical test and these two came up, is there a difference because the appliance is fastened to the wall? can someone reference an area in the code book for me? Thanks!



1) A 20 amp rated branch circuit with #12 wire supplying a duplex receptacle can be loaded to a
maximum of amps.


1) A 20 amp rated branch circuit with a #12 wire supplying a fastened in place wall
air conditioner can be loaded to a maximum of amps.

 

[david luchini]

Working on an electrical test and these two came up, is there a difference because the appliance is fastened to the wall? can someone reference an area in the code book for me? Thanks!



1) A 20 amp rated branch circuit with #12 wire supplying a duplex receptacle can be loaded to a
maximum of amps.


1) A 20 amp rated branch circuit with a #12 wire supplying a fastened in place wall
air conditioner can be loaded to a maximum of amps.

The answer is 20A and 20A.

But I suspect they are thinking about 210.23(A)(1) and (2)...

 

[S'mise]

I think they are both 16amps. (210.19)

The exception for 100% rated breakers not withstanding. (Often test questions ignore the exceptions)

The AC fastened in place is a continuous load.

If it mentioned more than one fastened in place appliance I would agree 210.23 coming into play

 

[infinity]

I think they are both 16amps. (210.19)

The exception for 100% rated breakers not withstanding. (Often test questions ignore the exceptions)

The AC fastened in place is a continuous load.

If it mentioned more than one fastened in place appliance I would agree 210.23 coming into play

Based on what code section would an in-wall AC be a continuous load?

I agree with David 20 and 20.

 

[Little Bill]

I think they are both 16amps. (210.19)

The exception for 100% rated breakers not withstanding. (Often test questions ignore the exceptions)

The AC fastened in place is a continuous load.

If it mentioned more than one fastened in place appliance I would agree 210.23 coming into play

It doesn't have to be more than one fastened in place. It can be lighting loads or other not fastened in place along with fastened in place.

(2) Utilization Equipment Fastened in Place. The total
rating of utilization equipment fastened in place, other than
luminaires, shall not exceed 50 percent of the branch-circuit
ampere rating where lighting units, cord-and-plug-connected
utilization equipment not fastened in place, or both, are also
supplied.

 

[hurk27]

Based on what code section would an in-wall AC be a continuous load?

I agree with David 20 and 20.

440.32 80% or 16 amps table 210.2 directs us to 440.
440.62 requires a Room Air Conditioner to be cord and plug connected so the question does not state cord and plug connection so 440.32 should apply, but even if it was cord and plug connected 440.62(B) still requires the 80% rule, so to me that is saying that the NEC considers it continuous, air conditioners can very well operate over three hours to bring a room down to temp, and the rule in 440 seem to follow this thinking.

 

[infinity]

I see your point, the OP didn't mention if this were cord and plug and permanently installed or hard wired like a mini split system.

 

[S'mise]

It doesn't have to be more than one fastened in place. It can be lighting loads or other not fastened in place along with fastened in place.

Right, My point is that the 50% rating is for additional loads to the fastened in place Utilization equipment. So 210.23 does not apply to the OP.

If its a duplex outlet it needs to be rated 50%, if its an individual outlet or directly wired it does not.

 

[suemarkp]

440.32 80% or 16 amps table 210.2 directs us to 440.
440.62 requires a Room Air Conditioner to be cord and plug connected so the question does not state cord and plug connection so 440.32 should apply, but even if it was cord and plug connected 440.62(B) still requires the 80% rule, so to me that is saying that the NEC considers it continuous, air conditioners can very well operate over three hours to bring a room down to temp, and the rule in 440 seem to follow this thinking.

A normal fixed AC unit has an MCA value that takes the 80% factor into consideration. I would think a wall unit would too, so if it had a nameplate of 20A, that would already include the largest motor factor.

 

[S'mise]

The test is essentially asking if you know how to derate for continuous loads.

There are test answers and real world answers.

 

[suemarkp]

Then they should ask "what is the amp rating of largest continuous load that can be plugged into this receptacle". Too many of these test question take you down debatable paths and some nameplate values take this into consideration and some do not.

 

[kwired]

A normal fixed AC unit has an MCA value that takes the 80% factor into consideration. I would think a wall unit would too, so if it had a nameplate of 20A, that would already include the largest motor factor.

If a wall unit has a factory cord and plug on it, I may be interested in actual load for service/feeder calculations but for the branch circuit why should I be concerned about actual load if it has a 20 amp cord cap? Voltage drop is about all that comes to mind. Now if it has a 15 amp cord cap I may be more interested in actual load because it may have a better chance of being 50% or less of 15 amps and I possibly could have other loads on same circuit more so then something with a 20 amp cord cap factory installed - those usually are going to be plugged into a dedicated individual outlet circuit.

 

[S'mise]

Yes I'm thinking your right, the first question should be 20A because it does not mention continuous loads.
I still think the second question should be 16A based on the fact that the AC can run for longer than 3 hours.

 

[suemarkp]

But they usually don't. I'd consider "normal" use of an HVAC unit to have it cycling on and off about every 15 minutes. That initial startup in a hot house is not normal use, and continuous means full load under normal usage.

 

[S'mise]

I am not aware of where it says "normal usage"

Continuous load; A load where the maximum current is expected to continue for 3 hours or more.
I interpret that as meaning a few hot days in July when the AC is running.

 

[kwired]

I'd be willing to bet that an air conditioner that has a rated full load of 16 amps may need more then a 20 amp breaker for starting purposes, making it a bad example to use for this type of question. Most hardwired AC units with that kind of rating will call for at least 25 or 30 amp breaker.

 

[suemarkp]

I am not aware of where it says "normal usage"

Continuous load; A load where the maximum current is expected to continue for 3 hours or more.
I interpret that as meaning a few hot days in July when the AC is running.

To me it is somewhat implicit in the word "expected". I don't expect a window HVAC to run continuously for 3 hours or more unless it is grossly undersized. Yes, it could run for more than 3 hours, but that wouldn't be typical so I don't expect it. I also don't expect the thermostat to fail or a contactor to stick where it could in fact run continuously without cycling.

I still say its a crappy example for a test question if they wanted to know that you knew about continuous loads. They should just ask the question with that word or make it more explicit in the question such as "where a light will be plugged in and is expected to be on for 8 hours continuously".

 

[S'mise]

To me it is somewhat implicit in the word "expected". I don't expect a window HVAC to run continuously for 3 hours or more unless it is grossly undersized. Yes, it could run for more than 3 hours, but that wouldn't be typical so I don't expect it. I also don't expect the thermostat to fail or a contactor to stick where it could in fact run continuously without cycling.

I still say its a crappy example for a test question if they wanted to know that you knew about continuous loads. They should just ask the question with that word or make it more explicit in the question such as "where a light will be plugged in and is expected to be on for 8 hours continuously".

I would rather error on the side of caution and calculate for the largest load I expect would ever happen.

I agree, a window AC unit running for 3 hours might not be a "normal" condition, but if it is anticipated that it can run (without a stuck contactor) for that long, It needs to be considered continuous. I agree "normal" if you mean; functioning as designed but not "normal" as in "normally it only runs for this long".

Under normal circumstances I don't leave the lights on for more than 3 hours either, but I expect at some point my kids probably will.

 

[hurk27]

To me it is somewhat implicit in the word "expected". I don't expect a window HVAC to run continuously for 3 hours or more unless it is grossly undersized. Yes, it could run for more than 3 hours, but that wouldn't be typical so I don't expect it. I also don't expect the thermostat to fail or a contactor to stick where it could in fact run continuously without cycling.

I still say its a crappy example for a test question if they wanted to know that you knew about continuous loads. They should just ask the question with that word or make it more explicit in the question such as "where a light will be plugged in and is expected to be on for 8 hours continuously".

The same can be said about electric heating but the nec still requires it for space heating(424.3(B)

Not all room AC units will have a MCA/MOCP rating and is allowed in 440.4(B) exception 1,2 and 3

Without this 440 will require the circuit to be sized at 125% in most all cases including a cord and plug connected AC unit it clearly requires it to be at 80% of the circuit(440.62(B).

I think the reason the NEC didn't include the requirement of AC units to be considered as continuous like it did for heat is because of the MCA/MOCP rules which would make it even more confusing as even now we have inspectors still trying to require us to derate the circuit another 80% even with the MCA/MOCP on the unit.

As for the OP test question I think this test was written back in the days before we had MCA/MOCP rules to go by, at least this one question was???

 

[suemarkp]

You are right with 440.62, it is clear a window AC unit is limited to 80% of a circuit's rating when there are no other loads on the circuit, and 50% if there are other loads are supplied.