Wires Ampacity.

[VENgineer]

I reviewed an installation with the following conductors, and I am requesting to change the cables or the OCPD. (I am only pointing out the violations.) Is this approach correct, or am I missing any demand factors that would allow for a reduction in cable size?

I understand that only tap conductors can have a smaller ampacity than the OCPD because they are protected by the overload device of the load's breaker.

 

[jim dungar]

Breakers do not protect the conductors on their 'line side'.
You need to know the size of the upstream breaker in order to judge their adequacy.

This appears to be service entrance equipment. Service entrance conductors sizing might come from the POCO.

 

[Dennis Alwon]

View attachment 2571795

I reviewed an installation with the following conductors, and I am requesting to change the cables or the OCPD. (I am only pointing out the violations.) Is this approach correct, or am I missing any demand factors that would allow for a reduction in cable size?

I understand that only tap conductors can have a smaller ampacity than the OCPD because they are protected by the overload device of the load's breaker.

4/0 aluminum is compliant on a 200 amp overcurrent protective device because this appears to be a dwelling unit. Each feeder that carries the entire load of the dwelling is allowed to use this table below

Also 4/0 is good for 180 amps and because of 240.4(B) we are allowed to use a 200 amp overcurrent protective device as long as the load doesn't exceed 180 amps

 

[wwhitney]

4/0 Al has a 75C ampacity of 180A, and 1/0 Al has a 75C ampacity of 120A. Where the calculated load does not exceed these values, 240.4(B) permits protecting them at 200A and 125A, respectively.

So the only NEC violation in the sizes highlighted in red is the 1/0 Al protected at 150A. If those conductors are subject to the NEC, then the conductor should be upsized to at least 2/0 Al or the OCPD downsized to 125A.

Cheers, Wayne

 

[don_resqcapt19]

For the 125 amp circuits with 1/0 aluminum, you need to know the calculated load. If the load is 120 amps or less, the wire size is code compliant because of the rule in 240.4(B).

 

[VENgineer]

It is a commercial building with the following spaces:

• 1 accounting office.
• 1 dental clinic.
• 3 offices.

 

[VENgineer]

Thank you.
Now I see my mistake.
I am grateful every day for this forum and its help.

 

[Dennis Alwon]

It is a commercial building with the following spaces:

• 1 accounting office.
• 1 dental clinic.
• 3 offices.

Ok then 240.4(B) would apply depending on the load.... Glad we could help