Motor GF/SC Protection

[augie47]

This is a "spin-off" from a thread by LittleBill on a powering power to a pump motor and I've been unable to determine the answer.
The scenario is a 240v single phase motor (assume with internal OL protection) being fed from a 2-wire/2 wire 480 to 240v transformer.
Can the transformer primary serve as the motor SC/GF protection or would protection be required on the transformer secondary ??

 

[don_resqcapt19]

The transformer primary could provide the overcurrent protection for the secondary, but will be limited to 125% of the primary current, Is that enough to start the motor?

 

[wwhitney]

I'm thinking the concern is that 240.4(F) and 240.21(C)(1) address using the primary OCPD to protect the secondary conductors, but only covers the normal case where the conductors are protected at their ampacity (after multiplying by the voltage ratio).

So, for example, if you are using 240.4(F), seems like you can't also use 240.4(B) on the secondary conductors. And there doesn't seem to be any language permitting the use of the primary OCPD to provide Article 430 Part IV OCPD.

Too late for a 2026 PI, but seems like 240.4(F) and 240.21(C)(1) should just permit the primary OCPD to be treated as a secondary OCPD at a rating given by multiplying by the voltage ratio.

Cheers, Wayne