NEC 230.204 Isolating switches

[hydrogirl]

Can fuses on a 24.9kV line satisfy the requirements of the NEC 230.204 code? Here is the setup:

250 Hp 3P/60H/4160V motor with motor controller and a 4160V/24.9kV 300KVA padmount transformer

Thanks in advance for any help on this.
Sherry

 

[davidbeach]

Maybe, but I wouldn't. How do you lock out the removed fuses? Can you meet the requirements of 230.204(D)?

 

[hydrogirl]

We would like to install a fused disconnect between the motor controller and the transformer (4160V side) with an emergency shut off switch. The problem we are having is proving that this is a necessary item as required by the code. Our GM thinks the fuses on the high line pole on the 24.9kV side of the transformer are good enough. He is not an electrical eng or an electrician and neither am I or the maintenance supervisor, so we are seeking advice. Thanks very much for your help.
Sherry

 

[l3city]

Hi hydrogirl:
Well, question: Does your Motor Control Center has a main disconnect or a maximum of six disconnects as required by NEC?? This shall be of sufficient size as to deal with your 4160V XFMR. If the MCC comes with a main disconnect or has not more than 6 disconnects, than you will save some $$ buy not getting a fused disconnect cabinet. (Of course this is if you're only using this switching cabinet for you MCC only, otherwise you can use it for later electrical additions)

What is for sure is that you will need a way to disconnect your MCC (i.e. electrical service) and this is required by the NEC, check NEC 230.70 Part VI. In other words, there is no way you can just go with the primary side fuses.