NEC Article 450 Help

[FaradayFF]

Hi Gents,
I understand that article 450 provides guidance for sizing overcurrent protection devices for transformers. However, I didn't see any discussion on the location of the said protective devices. Say the circuit breaker providing primary protection to the transformer is located in the MCC, than this breaker would need to be sized such that it protects the feeder to the transformer as well. This would mean that the primary breaker functions not only as the protective device for the transformer but also for conductor protection. I didn't see any requirements in the article that the protective devices need to be installed AT the transformer.
Am I missing something?
It appears to me that both the transformer and the primary& secondary wiring need to be treated as one when sizing the breakers/fuses.

Thanks,
EE

 

[texie]

Yes, the OCPD for the transformer must also protect the conductors which is covered in Article 240.

 

[don_resqcapt19]

The rules in Article 450 only apply to the protection of the transformer itself. The rules in Article 240 cover the required protection of the primary and secondary conductors. Yes, the OCPD for the primary conductors almost always protects both the primary conductors and the transformer. There is no requirement that the primary OCPD be located near the transformer. There is a requirement in 450.14 for a disconnect within sight of the transformer, but that section goes on to say a remote lockable disconnect is permitted as long the location of the remote disconnect is marked on the transformer. The protection on the secondary most often provides both secondary conductor protection and where required the transformer secondary protection. Here again, there are no rules that require this protection be located at the transformer, however two of the most commonly used secondary conductor protection rules limit the conductor length between the transformer secondary terminals and the line side terminals of the OCPD to 10' or 25'. There are other rules that would permit longer lengths, including the one for secondary conductors that are outside of buildings... that one has no length limit.