110.3(B) rules when sizing A/C conductors.

[Terryb80]

Sizing the circuit for an A/C compressor....
According to 440.6(A) we size the wire and breaker per what is on the nameplate. A fairly common compressor will give values of “minimum circuit ampacity” of 30A and a “minimum overcurrent protection” of 50A. Here’s the problem... if you check the spec sheet for a 50A breaker (Siemens QP for example) it shows a wire range of #8-#6 conductors. 110.3(B) says we have to follow all published instructions when installing listed equipment. The breakers are listed to accept a minimum of #8 wire, but the installation allows for a #10 on a 50A breaker. This is done daily and passes inspection. I don’t see a problem as far as a safety or practical installation. I’m looking for clarification as the code is written.

Does landing the #10 violate the listing of the 50A breaker, thus creating a violation per the NEC?

 

[infinity]

Does landing the #10 violate the listing of the 50A breaker, thus creating a violation per the NEC?

Yes. In that case you would need to use a conductor that was at least as large as the minimum size of the conductor permitted on the terminal of that circuit breaker. You could always run the #10's and splice on a short piece at the CB to be code compliant with the terminal rating.

Welcome to the Forum.

 

[LarryFine]

A fairly common compressor will give values of “minimum circuit ampacity” of 30A and a “minimum overcurrent protection” of 50A.

It should say "maximum overcurrent protection" for the breaker/fuse.

Does landing the #10 violate the listing of the 50A breaker, thus creating a violation per the NEC?

Possibly, but if the terminal properly grips the #10 wire, I don't sweat it.

 

[infinity]

I looked at both Eaton and Siemens CB's in the 2 pole, 50 amp configuration. Siemens lists the conductor range from #8-#4, the Eaton CB lists the conductor range from #14-#1/0.

 

[jaggedben]

I looked at both Eaton and Siemens CB's in the 2 pole, 50 amp configuration. Siemens lists the conductor range from #8-#4, the Eaton CB lists the conductor range from #14-#1/0.

What did you actually look at for the Eaton? There's no way you can land 1/0 on a 50A BR.

 

[infinity]

What did you actually look at for the Eaton? There's no way you can land 1/0 on a 50A BR.

You might be right, the CB lists torque rating on the side of the breaker up to size 0.

 

[Terryb80]

Thanks, guys.
Yeah they do say “maximum overcurrent protection”. I just messed that up.
Infinity, that’s what I was thinking, but it never dawned on me to check the wire range of a breaker. As long as it clamped properly, I was good with it. A coworker posed the issue to me the other day and I had to investigate. That’s why I love this field.... never stop learning something new!

thanks
Terry

 

[electrofelon]

Sizing the circuit for an A/C compressor....
According to 440.6(A) we size the wire and breaker per what is on the nameplate. A fairly common compressor will give values of “minimum circuit ampacity” of 30A and a “minimum overcurrent protection” of 50A. Here’s the problem... if you check the spec sheet for a 50A breaker (Siemens QP for example) it shows a wire range of #8-#6 conductors. 110.3(B) says we have to follow all published instructions when installing listed equipment. The breakers are listed to accept a minimum of #8 wire, but the installation allows for a #10 on a 50A breaker. This is done daily and passes inspection. I don’t see a problem as far as a safety or practical installation. I’m looking for clarification as the code is written.

Does landing the #10 violate the listing of the 50A breaker, thus creating a violation per the NEC?

FWIW, the last few years I have been seeing max OCPD and MCA values that are pretty close to each other. Not sure if this is coincidence or a new "trend", but I think I recall some other people commenting on that too.

 

[LarryFine]

FWIW, the last few years I have been seeing max OCPD and MCA values that are pretty close to each other. Not sure if this is coincidence or a new "trend", but I think I recall some other people commenting on that too.

I would think that, the closer the numbers, the easier the unit is to start, or has higher running current.

 

[kwired]

I would think that, the closer the numbers, the easier the unit is to start, or has higher running current.

Or has a VFD or other control method that is "soft starting".

Across the line starting units that I have seen recently still have in neighborhood of twice MOCP of what MCA is.

 

[tortuga]

I looked at both Eaton and Siemens CB's in the 2 pole, 50 amp configuration. Siemens lists the conductor range from #8-#4, the Eaton CB lists the conductor range from #14-#1/0.

I imagine thats an omission on Siemens part, my guess it the lug on the 40-50A two pole breakers are good down to a #14, As there is almost no difference between the 2 pole 15-30's and the 2 pole 40-50's as to lug size.They probably never considered ART 440 or 430 but I am not Siemens.
It gets interesting if you go to a 60 Amp, Siemens has two different breakers with no distinction on part numbers one goes up to a 3 the other 2/0:

 

[kwired]

I imagine thats an omission on Siemens part, my guess it the lug on the 40-50A two pole breakers are good down to a #14, As there is almost no difference between the 2 pole 15-30's and the 2 pole 40-50's as to lug size.They probably never considered ART 440 or 430 but I am not Siemens.
It gets interesting if you go to a 60 Amp, Siemens has two different breakers with no distinction on part numbers one goes up to a 3 the other 2/0:

Question is are they still producing both or did they make a change and one is older than the other?