Tranformer OCP and conductor sizing

[Patrick86]

The NEC Code is new ground for me. I?ve followed the example for the 45kVA transformer in the following link: http://www.mikeholt.com/mojonewsarchive/NEC-HTML/HTML/TransformerInstallation~20020516.htm.

I have a contractor that insists that my OCP and conductor sizes are too high because transformers are only good for 80%. I do not see any guidelines in NEC or on the internet for derating transformers. Any comments on this would be appreciated.

 

[jim dungar]

I have a contractor that insists that my OCP and conductor sizes are too high because transformers are only good for 80%.

Your contractor is wrong.

There is no basis in the NEC for sizing protective devices based on anything other than 100% of the transformer nominal rating.
When someone says 'it is code' ask for a reference.

 

[texie]

Assuming I understand your OP, Mr. Holt is correct. The contractor is wrong.

 

[Patrick86]

Transformer OCPD and conductor sizing

Transformer OCPD and conductor sizing

Your contractor is wrong.

There is no basis in the NEC for sizing protective devices based on anything other than 100% of the transformer nominal rating.
When someone says 'it is code' ask for a reference.

Thanks for the input.

 

[infinity]

Your link is a good article from Mike Holt. Whoever is giving you this 80% information is incorrect.

Welcome to the Forum.

 

[SG-1]

If the transformer is located in some metalclad switchgear with an ambient temperature of 50 degrees C & restricted air flow the contractor is right.