mike holt said ......

[kwired]

What's the wiring method? #10 NM cable has a max breaker size of 30 amps.
Or am I missing something?

Ron

That small conductor rule doesn't apply to art 430, 440 or some other applications.

What can require NM to be larger in this situation is the fact it has to have it's ampacity determined from 60C column where most other conductors we use we can use the 75C ampacity column.

10 AWG @ 60C however does have max ampacity of 30 amps but overcurent protection for an art 440 application can be higher. The conductor is still protected from overloading by the motor overload protector.

 

[Buck Parrish]

ok so we follow 440.35 on conductor size and the name plate for OCPD size

You use the name plate for both. Minimum circuit ampacity and maximum breaker size.
It's been my experience if you don't use the maximum breaker size. You will get nuisance tripping.

 

[rc/retired]

That small conductor rule doesn't apply to art 430, 440 or some other applications.

What can require NM to be larger in this situation is the fact it has to have it's ampacity determined from 60C column where most other conductors we use we can use the 75C ampacity column.

10 AWG @ 60C however does have max ampacity of 30 amps but overcurent protection for an art 440 application can be higher. The conductor is still protected from overloading by the motor overload protector.

Many thanks.

Ron

 

[Treg the electrician]

This is a good video from Ryan Jackson too.

Rob G, Seattle

ok that video was awesome thank you

 

[LarryFine]

ok so let me get this straight, my breaker gives protection for short circuit and ground fault , and overcurrent is governed internally in the air conditioning equipment?

With equipment with integral over-current protection, yes.

 

[texie]

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.

It seems you are now clear on these rules from this discussion. The inspector is clearly wrong and needs training. I would absolutely call him on this. But, sadly, it is amazing to me how many in the trade, including inspectors, don't understand the concepts of sizing circuits such as this.
Very similar to sizing Art. 430 motor circuits. Just for grins I would ask him what size conductors are needed for, say, a 100 HP/480 volt motor that is fed with a 350 amp breaker. Does he really think that you would need conductors with an ampacity of 350 amps?

 

[sgtsparky]

Also remember that some inspectors don’t like homeowners doing there own work, so you need to understand the sizing rules (as others said some electricians do not know them).
I moved counties and was working on my home and the inspector flagged 5 or 6 things I said wait a minute grabbed my handbook and flipped to services and asked him what he was referring to, he said well that’s the way I like it, I said “cite it to write it” and after finding out I was a supervising general journeyman (Oregon) he signed off on all of them. Also code requires us to follow the manufacturer’s listing instructions, where someone referred to wire and breaker sizes is correct also 110.3.B. So there are multiple code backed allowances to use a smaller wire size than straight breaker sizing.

 

[don_resqcapt19]

ok so let me get this straight, my breaker gives protection for short circuit and ground fault , and overcurrent is governed internally in the air conditioning equipment?

It is only the overload protection that is provided internally in the equipment. The word "overcurrent" is a defined term that includes, short circuits, ground faults and overload. Overload protection can be provided by a device at any point on the circuit. Short circuit and ground fault protection can only be supplied by a device at the supply end of the circuit.

Overcurrent.
Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault.