Transformer Overcurrent Protection

[Saneva_72]

Do transformers need Overcurrent Protection Devices (OCPD) on both the primary and secondary sides? I understand that OCPDs are typically required to protect equipment from faults, but I’m wondering if both sides need separate protection or if one is sufficient. Additionally, what about isolation? Is it necessary to isolate both the primary and secondary circuits?

 

[D. Castor]

It depends. Refer to NEC Article 450 since you are in the US. Depends on transformer rating, voltage and some other factors. If you provide specifics, someone will probably give you a better response.

 

[don_resqcapt19]

Often you can provide primary only protection for the transformer itself, but it is a rare case that the secondary conductors do not need overcurrent protection per one of the rules in 240.21(C).
The rules for transformer protection are in 450.3.

 

[jim dungar]

Transformers only need primary side protection per 450.3.
The transformer secondary side conductors need protection per 240.21(C).

 

[ron]

Do transformers need Overcurrent Protection Devices (OCPD) on both the primary and secondary sides? I understand that OCPDs are typically required to protect equipment from faults, but I’m wondering if both sides need separate protection or if one is sufficient. Additionally, what about isolation? Is it necessary to isolate both the primary and secondary circuits?

As the others have said, you put OCPDs on both sides but for different reasons.

 

[Deltaforce]

Additionally, what about isolation? Is it necessary to isolate both the primary and secondary circuits?

yes but mv equipment enclosure and lv equipment enclosure bond together in building premise avail mv supply, a mv ground fault transfer potential to lv equipment which may hazard with respect to remote earth, proper bonding necessary.

 

[augie47]

yes but mv equipment enclosure and lv equipment enclosure bond together in building premise avail mv supply, a mv ground fault transfer potential to lv equipment which may hazard with respect to remote earth, proper bonding necessary.

I think I just heard a politician speak ... all the right words are there just not in a coherent manner.