Disconnecting Means Question

[Jennifer S]

I am currently designing a control panel that must have an isolation transformer supplying it. Do I have to have the main panel disconnect before the isolation transformer? I also have two other 1KVA transformer disconnects before the main disconnect (for lighting/PC/PLC). I would like to keep the isolation transformer before all of the panel devices including the transformer disconnects. I cannot find what NEC required to do. Can anyone recommend a location to look in NEC or anything else.

Thanks.

 

[petersonra]

Re: Disconnecting Means Question

Without having all the facts, i am kind of taking a stab at this, but generally, the NEC applys not to the machine (or parts of a machine like a control panel) but to the installation there of.

The actual design of the control panel for most machines would be covered by NFPA79 which specifically allows the PLC (and some other devices) to remain powered when the main disconnect is open.

 

[don_resqcapt19]

Re: Disconnecting Means Question

The NEC requires overcurrent protection for transformers, but does not require them to have a disconnecting means.
Don

 

[Jennifer S]

Re: Disconnecting Means Question

Thanks a lot, I will look over NFPA 79. I do have fuses on the primary and secondary of the transformer.