NEC 440.22 45A or 50A circuit breaker

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DW98

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I scheduled 45A 2P circuit breakers for heat pumps. On heat pump submittal, MCA = 29.2A, Max Fuse Size = 45A. contractor panelboard submittal lists 50A 2P circuit breakers. When reading max fuse size, do I have to consider this to be maximum circuit breaker size. Can I allow a 50A c/b as long as it doesn't exceed 250% of compressor RLA? 440.22(C) refers to manufacturer's overlaod relay table for motor controllers so I'm interpreting this as not applying to nameplate data for a compressor. Am I correct?

For the contractors: do you find 35A, 45A sizes readily available?
 
DW98 said:
I scheduled 45A 2P circuit breakers for heat pumps. On heat pump submittal, MCA = 29.2A, Max Fuse Size = 45A. contractor panelboard submittal lists 50A 2P circuit breakers. When reading max fuse size, do I have to consider this to be maximum circuit breaker size.
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If the unit states max fuse and does not state max fuse or breaker than you must use fuses.


Can I allow a 50A c/b as long as it doesn't exceed 250% of compressor RLA? 440.22(C) refers to manufacturer's overlaod relay table for motor controllers so I'm interpreting this as not applying to nameplate data for a compressor. Am I correct?
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You cannot protect the unit with the larger overcurrent protective device. It must be as stated on the nameplate

For the contractors: do you find 35A, 45A sizes readily available?
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Yes
 
NEC 240.4(B)

NEC 240.4(B)

Unless I am wrong (which I am sure you all will tell me if I am) the OCPD at the panel is in place to protect the wire. In that case 240.4(B) states that the next higher circuit breaker may be used. This is the case because you will probably have a hard time finding a 45amp CB. So a 50 amp is permissible
 
Look at your nameplate closely as they often "hide" the fact than a HACR breaker can be used in lieu of a fuse.
In recent years it has been my experience that heat pumps almost always accept breakers (refrigeration equipment often does not)
 
augie47 said:
Look at your nameplate closely as they often "hide" the fact than a HACR breaker can be used in lieu of a fuse.
In recent years it has been my experience that heat pumps almost always accept breakers (refrigeration equipment often does not)
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I agree that most, esp. residential, units always allow an HACR type breaker-- all the smaller breakers are rated HACR so it may be possible to do that but it stiill cannot be larger than the nameplate. Now you may be able to use a 50 amp overcurrent protective device in the panel with the proper size fuse or overcurrent protective device at the unit.
 
I took a look again at the download in the mechanical engineers folder and it does list max fuse/circuit breaker. If the contractor says he can't get a 45A c/b then I'll do what the two previous post suggest, use a 50A c/b for the wire and a fusible disconnect with 45A fuses. Thanks again.
 
Personally I would avoid fuses at the unit. Get the right size overcurrent protective device and put a non- fused diso at the unit
 
Joseph Alexander said:
Unless I am wrong (which I am sure you all will tell me if I am) the OCPD at the panel is in place to protect the wire. In that case 240.4(B) states that the next higher circuit breaker may be used. This is the case because you will probably have a hard time finding a 45amp CB. So a 50 amp is permissible
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I'm afraid you do have it wrong, on two counts. The first, 240.4(B) would permit the next standard higher overcurrent device, but 240.6(A) lists 45A as a standard ampere rating. You could not, therefore, substitute of 50A OCPD for a 45A OCPD.

The second, 240.4(G) permits specific conductors to be protected in accordance with the specific article for the conductor application, in this case Art. 440. This usually permits an OCPD which is already higher than the ampacity of the conductor. But 440 sets a Maximum (not to exceed) value. If the MOCP is 45, rounding up to 50 would not be acceptable.
 
DW98 said:
I took a look again at the download in the mechanical engineers folder and it does list max fuse/circuit breaker. If the contractor says he can't get a 45A c/b then I'll do what the two previous post suggest, use a 50A c/b for the wire and a fusible disconnect with 45A fuses. Thanks again.
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If you used a 50A c/b at the panel, and 45A fused disc at the unit, the wire from the panel would have to be at least #8 instead of #10.

If you used a 45A c/b at the panel, you could use #10 minimum from the panel to the unit.
 
david luchini said:
I'm afraid you do have it wrong, on two counts. The first, 240.4(B) would permit the next standard higher overcurrent device, but 240.6(A) lists 45A as a standard ampere rating. You could not, therefore, substitute of 50A OCPD for a 45A OCPD.

The second, 240.4(G) permits specific conductors to be protected in accordance with the specific article for the conductor application, in this case Art. 440. This usually permits an OCPD which is already higher than the ampacity of the conductor. But 440 sets a Maximum (not to exceed) value. If the MOCP is 45, rounding up to 50 would not be acceptable.
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David if the conductor is rated for 50 amps he can install a 50 amp breaker on the feeder and install 45 amp fuses from the disco. To me that is a waste of money but that is what I thought he was doing.
 
Dennis Alwon said:
David if the conductor is rated for 50 amps he can install a 50 amp breaker on the feeder and install 45 amp fuses from the disco. To me that is a waste of money but that is what I thought he was doing.
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Yes, you can do that (see Post #10.)

But that is not what was being suggested in Post #4.
 
With the MCA as small as it is, a 40A breaker would probably work just fine. You can go smaller than max breaker/fuse, but not larger.
 
DW98 said:
I scheduled 45A 2P circuit breakers for heat pumps. On heat pump submittal, MCA = 29.2A, Max Fuse Size = 45A. contractor panelboard submittal lists 50A 2P circuit breakers. When reading max fuse size, do I have to consider this to be maximum circuit breaker size. Can I allow a 50A c/b as long as it doesn't exceed 250% of compressor RLA? 440.22(C) refers to manufacturer's overlaod relay table for motor controllers so I'm interpreting this as not applying to nameplate data for a compressor. Am I correct?

For the contractors: do you find 35A, 45A sizes readily available?
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IMHO...430.52(c)(1) excep(2)(c) it allows to go beyound 250% of the FLA when the OCPD is not sufficient.

...Don't we need motor overload here?
 
m sleem said:
IMHO...430.52(c)(1) excep(2)(c) it allows to go beyound 250% of the FLA when the OCPD is not sufficient.

...Don't we need motor overload here?
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It's a heat-pump so Art 440 would augment 430 (440.3).
440.22(C) states the manufacturer's marked values can't be exceeded.
Overload is commonly taken care of internally per 440.52(A)
 
Be careful as 430.52 refers to the branch circuit. If the op uses fuses or overcurrent protective device at the unit then the wire from the panel to the disco is a feeder not a branch circuit
 
I marked up the panelboard submittal to provide 45A 2P circuit breakers. I don't know why the didn't submit it that way in the first place. thanks again for all the responses.
 
Dennis Alwon said:
Be careful as 430.52 refers to the branch circuit. If the op uses fuses or overcurrent protective device at the unit then the wire from the panel to the disco is a feeder not a branch circuit
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Yes, if the overload protection at the equipment is breaker. I would think we still need to size the OCPD at the panel as 430.52. Did i miss something here?
 
m sleem said:
Yes, if the overload protection at the equipment is breaker. I would think we still need to size the OCPD at the panel as 430.52. Did i miss something here?
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430.52 is for branch-circuit rating which now starts at your fuse.
The wiring between the panel breaker and the disconnect is now feeder wiring and thus 310.15(B)(16).

(That is the way I see it and if I'm wrong I'm sure Dennis will jump back in here and also clear me up.):D
 
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