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#20679 01/18/03 09:17 PM
Joined: May 2001
Posts: 30
Nevin Offline OP
Had a case this morning where I had a 50 amp FRS-R fuse in a GE 60amp disconnect fail. I was not around when it occured however by all indications it really "blew" [Linked Image]. The top was burned out of the fuse and the line conductors above it had the insulation charred. the Red arc sheild was melted and sagging. These fuses are on a air compressor motor and normal amp draw is 29amps free running and 31amps under full load. I replaced the burnt conductors and checked out everything else. There were no line to ground faults and the resistance on the motor windings all check out normal. I replaced the fuse and fired up the machine everything ran normal.
What are the chances of a fuse failing like that for no apparent reason except for being a defective fuse? This compressor with these fuses has been in service for 3-1/2 years with no problems.
This incident also just reinforced in my mind the importance of have all open knockouts plugged and using the appropriate enclosure for the enviroment (dust etc). With the fire that blown fuse must have created, It would have been an ideal source of fire had it not been contained inside a proper enclosure.

#20680 01/18/03 09:28 PM
Joined: Jul 2002
Posts: 175
Sounds like high reistance in the fuse clip or the wire terminal caused the overheating.

There isn't much that can "malfunction" in a fuse that has a sufficiently high interrupting rating.


#20681 01/19/03 12:45 AM
Joined: Apr 2002
Posts: 2,527
It's a judgment call, but overheated fuse clips can lose spring tension or 'bite'.

The books say one shouldn't be able to easily rotate [by hand] the fuse barrel.

#20682 01/19/03 01:16 AM
Joined: Nov 2000
Posts: 2,148
There is a product to help when the fuse clips have lost their spring. Look at the TRON Clip-Clamps near the bottom of this page.

#20683 01/19/03 06:05 AM
Joined: Dec 2001
Posts: 300
I've come across fuses that were broken in half a few times. I figured that they burst or broke when they blew. No damage just alittle cleanup.

I suspect your burned wires and melted arc shield didn't happen in this instantaneous flash but that these things were hot for a long time from loose lugs or corrosion. Thats what I've seen melt those plastic arc shields and the wire insulation. Sometimes those arc shields look like a dali painting

[img] [/img]

#20684 01/19/03 09:12 PM
Joined: Jan 2003
Posts: 134
Nevin...actually these fuses are under size per code.your FRS-R fuses (time delay)are calculated at 175% with your full load current of 31 amps x 175% = 54.25 amps you can go up to the next size 60 amps fuses.the 50 are under size.and maybe a loose connection on the wiring or the clip did not help either.

#20685 01/20/03 05:17 PM
Joined: Sep 2002
Posts: 83
Nevin, What voltage is your compressor running at? FRS-R's are rated for 250 Volts. If someone accidentally grabbed the wrong fuses out of the drawer, (I've seen it happen) and installed them into a 480 Volt circuit. The results from the insulation breakdown would be consistent with the damage you describe.

#20686 01/20/03 06:28 PM
Joined: Jul 2001
Posts: 599
JBD Offline
Bussmann FRS-R fuses are 600V rated.
It is their 250V family that is FRN-R.

#20687 01/20/03 06:30 PM
Joined: Jan 2003
Posts: 134
Pearlfish...there is no way you can put 250 volt fuses in a 600 volt fused disconnect switch or 600 volts fuses in a 240 volt fused disconnect switch.(they just will not fit)base on the fuses(FRS-R fuse) info.they are used on 480 volts circuits.rating 600 this case a motor load.

if it was 240 fuses the number would have been FRN-R

[This message has been edited by lighthouse (edited 01-20-2003).]

#20688 01/20/03 07:44 PM
Joined: Aug 2002
Posts: 402
Is the photo I see in the this post on the violations section?
It sure looks like what your decribe.

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