240.92(E)

[Wirenut9361]

Can anyone provide details to clarify what the code reference means? How do I determine if the primary OCPD multiplied by the transformer ratio is adequate to protect the secondary? Is it based on the inverse time curve of the primary OCPD? What is considered effective protection?

 

[tortuga]

240.92 (E) Protection by Primary Overcurrent Device. Conductors
supplied by the secondary side of a transformer shall be permitted
to be protected by overcurrent protection provided on the
primary (supply) side of the transformer, provided the primary
device time-current protection characteristic, multiplied by the
maximum effective primary-to-secondary transformer voltage
ratio, effectively protects the secondary conductors.

Thats a good one.
We have to define 2 things
1) primary device time-current protection characteristic
2) maximum effective primary-to-secondary transformer voltage
ratio
I'd wager primary-to-secondary transformer voltage ratio will do I have no idea what they mean by "maximum effective" in there.
Can you post the details of the voltages, transformer and breaker?

 

[jim dungar]

I believe that section is addressing the turns ratio after any taps versus the turns ratio from the nominal nameplate voltages.