mike holt said ......

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Treg the electrician

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mike holt said that on HVAC equipment you should always size your conductors off the MCA and your OCPD off the max .
so for instance you might have # 10 wires on a 40 amp breaker . I got called on this by a seattle inspector . I watched the video again and it sighted 440.6. I cant seem to make a coherent argument to support what i did . If the mike holt video is correct can anybody point me to the code that indicates what i did was correct so that i can make my case.
 
The conductors are sized according to the nameplate MCA. The OCPD can be sized based on the maximum ampacity on the nameplate. The conductor does not need to correspond in any way to the size of the OCPD.
 
Mike's statement is correct. 440.32 & 440.35 related to sizing your conductors and 240.4(G) allows you to use an ovecrurrent device larger than the conductor ampacity.
This allowance is due to the conductor having overload protection included in the AC unit and the need to address inrush currents
 
Treg the electrician said:
thank you i will study those
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Look at those section but understand that the overload inside the a/c will protect the wires from being overloaded. The overcurrent protective device (breaker) will protect against short circuit and ground fault. This is why the breaker can be sized larger as it will trip under those conditioned I mention and is not used to protect the a/c itself.
 
Treg the electrician said:
mike holt said that on HVAC equipment you should always size your conductors off the MCA and your OCPD off the max .
so for instance you might have # 10 wires on a 40 amp breaker . I got called on this by a seattle inspector . I watched the video again and it sighted 440.6. I cant seem to make a coherent argument to support what i did . If the mike holt video is correct can anybody point me to the code that indicates what i did was correct so that i can make my case.
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Did you use a circuit breaker when the equipment label specifies a fuse?
 
Can you post a picture of the equipment nameplate, and the exact violation the inspector called out?

As others have noted, it is quite correct to size the OCPD and conductors per the nameplate; the question is if the violation was an inspector mistake, or made on the basis of some other aspect of the installation.

-Jon
 
winnie said:
Can you post a picture of the equipment nameplate, and the exact violation the inspector called out?

As others have noted, it is quite correct to size the OCPD and conductors per the nameplate; the question is if the violation was an inspector mistake, or made on the basis of some other aspect of the installation.

-Jon
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let me get back to you on that . it was a virtual inspection .
 
rc/retired said:
What's the wiring method? #10 NM cable has a max breaker size of 30 amps.
Or am I missing something?

Ron
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NM cable would only need to meet the MCA so for #10 that would be 30 amps max. As an example it could be protected by a 40 or 50 amp OCPD if the max listed on the nameplate was 40 or 50 amps.
 
rc/retired said:
What's the wiring method? #10 NM cable has a max breaker size of 30 amps.
Or am I missing something?

Ron
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You are missing the part in 240.4 that states "unless otherwise permitted by (F) & (G)" and Art 440 is listed in "G" therefore exempt from the "30 amp rule"
 
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