HVAC - HCAR Breakers vs conductor size being protected

[ngd4130]

I take this to the forum because I have seen a lot of confusion on this subject. I am under the impression the HCAR breaker size is to protect the conductor according to Table 310.15. This was the info sent to me which I believe is an opinion. Can the forum help to solve this confusion. Thanks.

"Motor circuits divide the two separate functions of an overcurrent protection device. “Overloads” are currents that can damage a circuit if allowed to continue for a sufficient time, whereas “short circuits” and “ground faults” are high currents that can cause immediate damage. Large motors and air conditioners separate these overcurrent functions. The breaker or fuse ahead of the air conditioner only protects against short circuits and ground faults. Overload protection is built into the compressor itself. The wire to a condensing unit must be large enough to allow the equipment to start. The device is therefore NOT sized to protect the wire against overloads. It is not uncommon to see a 50 Amp breaker on a #10 wire. The wire is protected against overloading by a separate thermal protection inside the compressor.

How do we know what the motor requires for wire size and proper fuse/breaker protection? It’s all on the mfg. label attached to the appliance. If the label calls for fuses, there MUST be a fuse in the disconnecting means, not a circuit breaker. If the label calls for a “HACR” type breaker (Heating, Air Conditioning and Refrigeration), then that is the type of breaker that must be used. If the label simply states “maximum sized over current protection” then any form of overcurrent protection may be used. The HACR designation is not always visible on a circuit breaker once it is installed inside a panel or disconnect.

Note on the label taken from a Lennox A/C data plate:

MIN. CKT. AMPACITY - 17.7.
MAX. FUSE - 25 UL (CSA is a Canadian standard. We use UL in the U. S.)
MAX. HACR TYPE CKT. BKR. - 25 UL
MAX. CKT BKR. UL - Not allowed in U. S.

All this means is the MINIMUM wire size required is #12 (solid copper); the MAXIMUM rating of a fuse (if a fuse is used) must be 25 amps and the MAXIMUM rating of a circuit breaker (if used) must be 25 amps AND the breaker must be a HACR type."

 

[augie47]

It is basically accurate.
Conductor size based on MCA, Fuse or Breaker on MaxOCP.

(We could complicate it by discussing Romex vs THWN and terminal temp ratings (110.14) but what you posted is a good rule of thumb)

 

[busman]

Also, it should be HACR.

 

[jim dungar]

All breakers listed to UL489 are HACR and have been for some 20 years or longer.
Putting a specific HACR label on these breakers is optional and therefore only offered as a special by some manufacturers.

 

[Dennis Alwon]

I'm sorry but I don't see your confusion as you have it correct. I think the biggest issue is that many electricians have been taught that #12 is 20 amps and must have a 20 amp overcurrent protective device that they cannot accept that a 35 or 40 amp breaker may be allowed.

FWIW, at least on residential units, I have noticed that there usually isn't a big gap between wire size and breaker size. I have seen many with a 26 amp mca and a 30 max overcurrent protective device.

 

[ngd4130]

I take this to the forum because I have seen a lot of confusion on this subject. I am under the impression the HCAR breaker size is to protect the conductor according to Table 310.15. This was the info sent to me which I believe is an opinion. Can the forum help to solve this confusion. Thanks.

"Motor circuits divide the two separate functions of an overcurrent protection device. “Overloads” are currents that can damage a circuit if allowed to continue for a sufficient time, whereas “short circuits” and “ground faults” are high currents that can cause immediate damage. Large motors and air conditioners separate these overcurrent functions. The breaker or fuse ahead of the air conditioner only protects against short circuits and ground faults. Overload protection is built into the compressor itself. The wire to a condensing unit must be large enough to allow the equipment to start. The device is therefore NOT sized to protect the wire against overloads. It is not uncommon to see a 50 Amp breaker on a #10 wire. The wire is protected against overloading by a separate thermal protection inside the compressor.

How do we know what the motor requires for wire size and proper fuse/breaker protection? It’s all on the mfg. label attached to the appliance. If the label calls for fuses, there MUST be a fuse in the disconnecting means, not a circuit breaker. If the label calls for a “HACR” type breaker (Heating, Air Conditioning and Refrigeration), then that is the type of breaker that must be used. If the label simply states “maximum sized over current protection” then any form of overcurrent protection may be used. The HACR designation is not always visible on a circuit breaker once it is installed inside a panel or disconnect.

Note on the label taken from a Lennox A/C data plate:

MIN. CKT. AMPACITY - 17.7.
MAX. FUSE - 25 UL (CSA is a Canadian standard. We use UL in the U. S.)
MAX. HACR TYPE CKT. BKR. - 25 UL
MAX. CKT BKR. UL - Not allowed in U. S.

All this means is the MINIMUM wire size required is #12 (solid copper); the MAXIMUM rating of a fuse (if a fuse is used) must be 25 amps and the MAXIMUM rating of a circuit breaker (if used) must be 25 amps AND the breaker must be a HACR type."

So let's get more specific: let us assume an RTU as a new installation. The nameplate of the RTU lists the following: MCA = 29; Max fuse or HACR Breaker = 45; minimum fuse disconnect = 29. Based on this info (or is more info needed?), what is the minimum size conductor from the panel to the unit disconnect switch? And what NEC code section supports this? Thanks.

 

[david luchini]

So let's get more specific: let us assume an RTU as a new installation. The nameplate of the RTU lists the following: MCA = 29; Max fuse or HACR Breaker = 45; minimum fuse disconnect = 29. Based on this info (or is more info needed?), what is the minimum size conductor from the panel to the unit disconnect switch? And what NEC code section supports this? Thanks.

#10 awg. Code section would be 430.24 or 440.33, 440.34.

 

[garbo]

I'm sorry but I don't see your confusion as you have it correct. I think the biggest issue is that many electricians have been taught that #12 is 20 amps and must have a 20 amp overcurrent protective device that they cannot accept that a 35 or 40 amp breaker may be allowed.

FWIW, at least on residential units, I have noticed that there usually isn't a big gap between wire size and breaker size. I have seen many with a 26 amp mca and a 30 max overcurrent protective device.

Several times I had to place an air compressor that had a nameplate around 21 -22 amps but a 30 amp breaker or time delay fuse would open up so went with a 40:amp fuse or breaker. These were in commercial garages that needed 140 to 150 # of air pressure to lift up loaded 48' trailors . When we used quality time delay fuses like the old Chase Shut brand usually a fuse sized only 125% larger would hold vast majority of the time I'm old school and prefer to have motors protected by a quality fused safety switch in the event that I might have to increase say a 20 amp fuse to a 25 amp. Easily done and did not have to put on my PPE and open up a large panel like you would need to do to upsize a circuit breaker.

 

[ngd4130]

#10 awg. Code section would be 430.24 or 440.33, 440.34.

430.24 - Several Motors or a Motor(s) and Other Load(s) - 125% of the full-load current of the highest rated motor.
440.32 - Single Motor-Compressor - not less than 125% of either the motor-compressor rated-load current or the branch-circuit selection current, whichever is greater.
440.33 - Motor-Compressor(s) With or Without Additional Motor Loads - 25% of the highest motor-compressor or motor full load current in the group.

So I am not seeing how the #10 AWG fits into this scenario?

 

[david luchini]

So I am not seeing how the #10 AWG fits into this scenario?

Add them all up, and you need a conductor with an ampacity not less than 29.

#10 has an ampacity of 35....35 is not less than 29, so #10 would be the minimum conductor size. (#12 has an ampacity of 25, so it is too small.)

 

[don_resqcapt19]

....

All this means is the MINIMUM wire size required is #12 (solid copper); the MAXIMUM rating of a fuse (if a fuse is used) must be 25 amps and the MAXIMUM rating of a circuit breaker (if used) must be 25 amps AND the breaker must be a HACR type."

All listed breakers have been HACR, even if not so marked for a couple of decades now.

 

[ngd4130]

Add them all up, and you need a conductor with an ampacity not less than 29.

#10 has an ampacity of 35....35 is not less than 29, so #10 would be the minimum conductor size. (#12 has an ampacity of 25, so it is too small.)

I agree 35 is more than 29. So, what about the 125% in two of your references and 25% in your other reference? 29 x 125% = 36.25 amps; 29 x 25% = 7.25 amps. What am I missing?

 

[LarryFine]

If the equipment specifies MCA and MOC, use those numbers. There is no math for anyone to do.

 

[david luchini]

I agree 35 is more than 29. So, what about the 125% in two of your references and 25% in your other reference? 29 x 125% = 36.25 amps; 29 x 25% = 7.25 amps. What am I missing?

The RTU manufacturer already calculated the 125% of the largest motor plus the other loads. That is how the arrived at the 29MCA on the nameplate.

 

[ngd4130]

The RTU manufacturer already calculated the 125% of the largest motor plus the other loads. That is how the arrived at the 29MCA on the nameplate.

MCA = Minimum Circuit Amps. So 29 MCA x 125% = 36.25 amps; hence 45 amp max fuse or HACR breaker. Since the MCA calculations are all internal, it would be nice to see the nameplate spelled out that way so there is no confusion.
In the situation I am looking at, the contractor wants to use #10 AWG off a 30-amp 3-pole breaker to feed the RTU. Thoughts?

 

[david luchini]

MCA = Minimum Circuit Amps. So 29 MCA x 125% = 36.25 amps; hence 45 amp max fuse or HACR breaker.

That is not how MOCP is calculated. See 430.53, 430.54, and 440.22. There is no reason to multiply the 29 MCA by anything.

In the situation I am looking at, the contractor wants to use #10 AWG off a 30-amp 3-pole breaker to feed the RTU. Thoughts?

Why not #10AWG off a 45A 3-pole c/b?

 

[jmellc]

I'm sorry but I don't see your confusion as you have it correct. I think the biggest issue is that many electricians have been taught that #12 is 20 amps and must have a 20 amp overcurrent protective device that they cannot accept that a 35 or 40 amp breaker may be allowed.

FWIW, at least on residential units, I have noticed that there usually isn't a big gap between wire size and breaker size. I have seen many with a 26 amp mca and a 30 max overcurrent protective device.

For sure. I too stay locked into 12/20, 10/30, etc. It was drilled into me. Similar issue, I always hated running an HVAC circuit ahead of equipment arriving. Several times, I ran what was ordered, then the unit needed a bigger circuit. I started calling the HVAC guys to verify. Also, seeing multiple listing nameplates where the heat strips were supposed to be checked off on the nameplate. Sometimes that wasn’t done & I had to call someone.

 

[ngd4130]

That is not how MOCP is calculated. See 430.53, 430.54, and 440.22. There is no reason to multiply the 29 MCA by anything.


Why not #10AWG off a 45A 3-pole c/b?

I am think the proper code section is 440.52(A) & (B). It refers to Motor-Compressor and Branch-Circuit Protection. It also lists 156% as one of the methods (29 MCA x 156% = 45.24 = 45 amp HACR breaker).

 

[david luchini]

I am think the proper code section is 440.52(A) & (B). It refers to Motor-Compressor and Branch-Circuit Protection. It also lists 156% as one of the methods (29 MCA x 156% = 45.24 = 45 amp HACR breaker).

440.52 doesn't say anything about Branch Circuit Short Circuit and Ground Fault Protection....440.22 does.

Even then, 440.52 doesn't tell you to use the MCA anywhere in overload calculations.

 

[jim dungar]

All listed breakers have been HACR, even if not so marked for a couple of decades now.

I think it is just the ones listed to UL489. I wouldn't be surprised if it is near 30 years now.