Coordination and Feeders
Coordination and Feeders
(OP)
First post here...this looks like a great forum.
Here's my situation: I have a drive/control panel whose FLA draw is 65A on the 480V line. The manufacturer has sized the main disconnect fuses at 110A. I'd like to coordinate my feeder breaker with this fusing, but I'm realizing that it will likely require a fairly large-frame breaker and upsized wire to the panel to get acceptable coordination. It seems silly to me to have a (guessing here) 250A breaker feeding a panel whose FLA is 65A. Since selectivity isn't an issue here (popping the breaker or blowing the fuses takes down the same loads, after all), I'm thinking that I may be able to keep my feeder to a reasonable size by not worrying terribly about coordination.
My question is this: When sizing protection for feeders to drive/control panels, what approach do tyou generally take?:
1) Upsize and coordinate the feeder breaker/fuses to provide coordination with the panel breaker/fuses
2) Match or slightly upsize feeder protection to panel breaker/fuses to allow for a smaller feeder.
Thanks for your help.
Here's my situation: I have a drive/control panel whose FLA draw is 65A on the 480V line. The manufacturer has sized the main disconnect fuses at 110A. I'd like to coordinate my feeder breaker with this fusing, but I'm realizing that it will likely require a fairly large-frame breaker and upsized wire to the panel to get acceptable coordination. It seems silly to me to have a (guessing here) 250A breaker feeding a panel whose FLA is 65A. Since selectivity isn't an issue here (popping the breaker or blowing the fuses takes down the same loads, after all), I'm thinking that I may be able to keep my feeder to a reasonable size by not worrying terribly about coordination.
My question is this: When sizing protection for feeders to drive/control panels, what approach do tyou generally take?:
1) Upsize and coordinate the feeder breaker/fuses to provide coordination with the panel breaker/fuses
2) Match or slightly upsize feeder protection to panel breaker/fuses to allow for a smaller feeder.
Thanks for your help.





RE: Coordination and Feeders
RE: Coordination and Feeders
David Baird
Sr Controls Designer
EET degree.
Journeyman Electrician.
RE: Coordination and Feeders
The fuse is for panel protection, the breaker is for cable protection. The issue looks like they wanted to be able to find the fault quickly (I don't know why, as they can't fix it quickly).
The fuse, unless it is a current limiting, should coordinate down. The breaker maybe sized such that the fast trip (inst) will not operate at those fault current levels.
RE: Coordination and Feeders
I'll try to achieve coordination with a breaker that's slower than the fuses in the panel. I really don't want to upsize my switchboard to something ridiculously large.
RE: Coordination and Feeders
I would definately leave the fuse there in case it is providing some fault limiting protection for the equipent in your panel.