Fuses

tpd

Member
What would a fast acting current limiting fuse be considered as? A time delay or non time delay for sizing purpose. We have a 4160 volt 250 hp motor - 33 FLA with 70 amp motor circuit current limiting fuses that blow on starting. Very expensive! The next size fuses are 100 amp. Is this acceptable to go to this size?
 

tpd

Member
Motor is fine. This is not the only piece of equipment we have had this problem on. This plant has been mothballed for a few years and I've been told that someone was re-sizing just before they shut it down. I think that the fuses were larger size before. So possibly they are pulling a load on starting and this is the reason fuses are blowing. They don't blow every time either. I think it's just that we are bordering on the fuse limit and the next size is quite a bit larger.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
What would a fast acting current limiting fuse be considered as? A time delay or non time delay for sizing purpose. We have a 4160 volt 250 hp motor - 33 FLA with 70 amp motor circuit current limiting fuses that blow on starting. Very expensive! The next size fuses are 100 amp. Is this acceptable to go to this size?
Still wouldn't hurt to test the motor. I'm not a fuse expert by any means, but from my experience, a fast acting fuse is not a time delay fuse, if that helps any.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Engineer
Current limiting and time delay are not mutually exclusive.

Medium voltage fuses for motor applications, are not usually sized by continuous amps like 480V ones are.

I have never heard of a 70A MV motor fuse, I would expect to see an 'R' rating instead.
 
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