Secondary Protection Needed?

[charliemalbrough]

Is it absolutely necessary to install an overcurent protection device immediately after a transformer (three phase) or is the overcurrent device on the primary sufficient, or does the tap rule apply, or can a main breaker on the panel that the transformer feeds do the job? I know it doesn't protect the feeder itself, but where in the code does it say that the secondary protection is absolutely necessary?

 

[infinity]

For most three phase transformers secondary conductors will require OCP. Take a look at 450.3(B)

 

[iwire]

450 does not require protection of the conductors, only the transformer.

I know it doesn't protect the feeder itself, but where in the code does it say that the secondary protection is absolutely necessary?

240.21(C) is where we find the OCP requirements for the transformer secondary conductors.

For the common 480 - 208Y/120 transformer it will be 240.21(C)(2) that applies.

 

[infinity]

Bob's got it right, I gave the incorrect article for conductor protection. Mike Holt has a good article in the Feb. 2008 EC&M magazine regarding transformer secondary conductor protection.