5kv motor branch circuit protection

[winslowfam]

Hi...I have an existing 5kv motor starter with overcurrent and fault protection built in. This starter is fed from a fused switch in a 5kv switchboard. The feeder conductor size from the switchboard to the starter is the same size as the motor leads. I know the motor leads are protected from overcurrent by the overload relays in the starter. The question is...is the feeder conductor from the switchboard also protected against overload by the motor overload relay and only protected against fault current by the feeder fused switch fuse ? Or does the feeder fused switch fuse need to be sized to protect the feeder conductors against overload as well as fault current? Is it all considered a motor circuit, or is it considered a branch circuit from the switchboard to the starter ? Thanks.

 

[david]

Re: 5kv motor branch circuit protection

I would look at this as a motor circuit. Are the conductors feeding the motor starter sized FLA based on the tables in the NEC plus 25%? Properly sized OL?S would provide over current protection for the motor circuit.

 

[frenchelectrican]

Re: 5kv motor branch circuit protection

also i will suggestion that the 5KV motors fuse and ol relay will work somehow little diffrent than the low votage system (600v or less ) but my suggestion to look at the bussman fuse they did have listing for the meduim voltage motor appactions there and it will show the curve for the current and time to blow out


merci marc