Transformer Secondary Protection

[sbutler]

I have a project where I am using a 480V, 60HZ to 50HZ inverter to generate 50HZ, 400V. The primary is protected by a main CB. The output runs approximately 200' to a main power panel with MCB. Does the secondary require OCP?

 

[don_resqcapt19]

I have a project where I am using a 480V, 60HZ to 50HZ inverter to generate 50HZ, 400V. The primary is protected by a main CB. The output runs approximately 200' to a main power panel with MCB. Does the secondary require OCP?

The secondary of the transformer itself may not require protection, but the secondary conductors will have to be protected per one of the rules in 240.21(C). In a couple of special cases the primary OCPD can be sized to protect the primary, the secondary and the secondary conductors. This can only be done where the transformer is a two wire to two wire, or where the transformer is a 3 wire delta/delta. In all other cases the secondary conductors require additional protection.

 

[Smart $]

Is there really a transformer involved?

 

[jeremy.zinkofsky]

I have a project where I am using a 480V, 60HZ to 50HZ inverter to generate 50HZ, 400V. The primary is protected by a main CB. The output runs approximately 200' to a main power panel with MCB. Does the secondary require OCP?

If we are calling the inverter a XFMR, then secondary OCP is not required as long as ALL of the conditions of NEC 240.21(C)(1) through (C)(6) are met. Your situation sounds like it will not meet the 240.21(C)(1) requirement, hence an OCPD for the secondary conductors.

 

[petersonra]

I don't see how an inverter can be treated like a transformer for code purposes as it is not a transformer.

Most inverters I have seen have built in OCPD on the output, or at least tell you what is needed in the instructions.

 

[Tom the lectrician]

I'm gonna say yes..

I'm gonna say yes..

Yes it does. I would treat it like any other device and protect it. Didn't you say it's going to a main circuit breaker? That would serve as the ocp for the wiring and device right? Any thing that is essentially changing the voltage/ ampacity is going to need protection for that rated voltage and ampacity. What exactly is thus feeding ,, an mcc?