Type R MV Motor Fuses

[philly]

In our plant we have several Type R motor fuses on our MV motors. In researching I have learned that these fuses are there for short circuit protection only. I also understand that these fuses are selected based upon application guides which specify fuse sizes based upon current, and motor acceleration times.

My question is, if these fuses are only there for short circuit protection then what risk is there of just arbitrarilly choosing a fuse that may be too large, or larger than what an application guide recommends. Are there any rules or codes that govern the maximum size of these fuses for a given application.

 

[Jraef]

It has to be coordinated with your motor controller. The overload relay and contactor are selected based on the fuse curve, so the entire system is a unit. Yoiu are not supposed to be willy-nilly changing anything on a MV motor.

 

[mull982]

It has to be coordinated with your motor controller. The overload relay and contactor are selected based on the fuse curve, so the entire system is a unit. Yoiu are not supposed to be willy-nilly changing anything on a MV motor.

The contactor is able to withstand up to to I believe a 36R fuse. The overload relay curve falls to the left of the fuse we have now. With this being the case say I have a 3R and the overload relay relay ends where the fuse picks up. What happens if I only have a 7R or larger fuse laying around and decide to put that in instead?

The only thing I can see visibally is that there might be a gap between where the curve ends and where the fuse would pickup. It would be possible that in this gap the current magnigute would not trip anything and therfore persist.

Any information I can look at to learn more on this application?