Minimum Circuit Ampacity - Is this the wire amps OR the wire and power supply amps?

[jumper]

From an NEC perspective, there isn't much guidance on sizing a transformer and what value to use (i.e. article 220 vs actual) In fact, there isn't even anything other than 110.3 that says you can't overload a transformer (although 450.3 puts an indirect limit on it). I think that mca/next size up from mca is probably good practice, but I also think one could go a little lower code compliantly.

I agree. No real guidance.

Like using this thread as an example. MCA-24A, we will use 240V. 5760VA.

Do you spec a 6kVA or a 9kVA?

 

[electrofelon]

I agree. No real guidance.

Like using this thread as an example. MCA-24A, we will use 240V. 5760VA.

Do you spec a 6kVA or a 9kVA?

I would prolly go 6. In my experience, hvac units almost always draw 2/3 of mca, so it's already 50% larger than the current it will see.

 

[jumper]

I would prolly go 6. In my experience, hvac units almost always draw 2/3 of mca, so it's already 50% larger than the current it will see.

:thumbsup:

 

[don_resqcapt19]

The NEC allows for the use of the "next closest size" circuit breaker, which would be 25A... 240.4(B). The term "MOCP" by the way is never defined or mentioned in the NEC. ...

I am not aware of any code section in the NEC that would permit the use of a 25 amp OCPD, where the nameplate has specified the maximum rating of the OCPD to be 24 amps.

 

[jumper]

I am not aware of any code section in the NEC that would permit the use of a 25 amp OCPD, where the nameplate has specified the maximum rating of the OCPD to be 24 amps.

And 440.4(B) says it has to be marked on the nameplate.

.....maximum rat- ing of the branch-circuit short-circuit and ground-fault pro- tective device.....