Transformer Secondary OCPD

[davelectric]

I am installing a 45 kva xfmr 240 volt primary delta to 120/208 wye secondary. Primary breaker is 125 amp. Is it necessary to have secondary protection per tap rules or can I install 150 amp secondary breaker at panel located 100 ft away. Feeders run thru inside of building

 

[david]

Re: Transformer Secondary OCPD

I do not consider the secondary conductors of a transformer ?Taps? but 240.21(c) deals with the secondary of a transformer. Indoor secondary conductors 100ft would need over load protection.

 

[davelectric]

Re: Transformer Secondary OCPD

I understand it needs overcurrent protection but I dont have enough space in electric rm to fit disconnect at transformer

 

[iwire]

Re: Transformer Secondary OCPD

Hang the transformer and use the space for the disconnect?

 

[charlie]

Re: Transformer Secondary OCPD

David, where you are protecting the transformer with the appropriate overcurrent protection, you are not protecting the secondary conductors. The exception to this statement is shown in 240.4(F), all others are transformer tap conductors and are covered in 240.21(C).

 

[charlie b]

Re: Transformer Secondary OCPD

Forgive a naive question, but where did you get the 3-phase 240 volt primary source? I?ve not run across such an animal. I infer it must exist, for you cannot get a single phase 120/208 from a single phase primary.

 

[goodcode]

Re: Transformer Secondary OCPD

Hey guys, that utility guy Charlie has hit the nail on the head.
In most cases the NEC considers transformer secondary conductors to be "tap conductors." The exceptions are listed in 240.21.
Way to go "Utility Guy."

 

[ryan_618]

Re: Transformer Secondary OCPD

Originally posted by goodcode:
Hey guys, that utility guy Charlie has hit the nail on the head.
In most cases the NEC considers transformer secondary conductors to be "tap conductors." The exceptions are listed in 240.21.
Way to go "Utility Guy."

LOL It might help that Charlie is on the code making panel responsible for article 240!

 

[goodcode]

Re: Transformer Secondary OCPD

Well now, that explains his prowess with what can be a complicated topic.
Thanks Ryan!

 

[charlie]

Re: Transformer Secondary OCPD

WOW! It would have been nice to have gotten us all together in SLC. Ryan is an inspector in SLC and Goodcode is a good friend of mine. Ryan, I assure you that you would like him if you ever met him. Maybe, one of these days, Goodcode will reveal his identity.