hot fuses

[electricalperson]

FPE fuse panel fed with a single phase 120/208 volt feeder. ambient tempature was 88 degrees. main fuse pullout was 141 degrees. 30 amp load on the panel. measured fall of potential across main lug to bus and had 100millivolt on each leg. im sure i know its loose connection. what do you guys think?

 

[mdshunk]

100mV is a lot. Better get some clip clamps on there or schedule the disco for replacement.

 

[jim dungar]

100mV is a lot. Better get some clip clamps on there or schedule the disco for replacement.

Manufacturer's of "clip clamps" say they are to keep fuses from falling out due to vibration, they are not for "improving" poor connections.

IMO, replace the device.

 

[mdshunk]

Manufacturer's of "clip clamps" say they are to keep fuses from falling out due to vibration, they are not for "improving" poor connections.

I'm certain that's what they say, but they're a fantastic stop gap until proper repairs can be made. That's the difference between what manufacturers say and how things are really done.

 

[JohnJ0906]

Slightly off topic

Slightly off topic

What would be a good tester to measure fall-of-potential?
My DMM doesn't measure at that level (mV)

 

[electricalperson]

i have a fluke 117 works pretty well.

 

[electricalperson]

i want to replace this panel ASAP. the main panel had a load of 150 amperes on it and it wasnt even close to being as hot as that little sub panel was. the guy said ever since some repair man replaced the fuses a few days ago it was that hot.

edit: fuses blew because the repair man pinched a wire between the can and the cover.

 

[fisherelectric]

clip clamps?

 

[electricalperson]

clip clamps?

sometimes you see those clipped around the knife blade fuse ends to stop them from coming out

 

[don_resqcapt19]

At least one manufacturer implies that the clips are to improve the connection.

TRON Clip-Clamps
Specifications
Decription:
Clamps for ferrule and blade-type cartridge fuse clips. Provides tight contact between fuse holder clips and fuse ferrules/blades.
Construction:
Phenolic knob and plated-steel jaws.

 

[mdshunk]

clip clamps?

I just noticed that he said it's a pullout, so it doesn't matter anyhow. Clip clamps are tightened around sidearm disconnect fuse terminals to squeeze the terminal tighter on the fuse blade or ferrule.

 

[iaov]

What would be a good tester to measure fall-of-potential?
My DMM doesn't measure at that level (mV)

I have a Fluke 87 that works very well.

 

[iaov]

If you clean the fuse ends and the fuse holders you may cure this problem.

 

[480sparky]

Could the heat be transferred from a loose termination?

 

[electricalperson]

Could the heat be transferred from a loose termination?

thats probably what it is. the repair man probably rigged fuses in there since it started when he changed the fuses. the first test i done before i removed a couple loads the mv reading was 230millivolts. my jaw nearly hit the floor. i tighted the lugs down as tight as i could without removing the fuses (couldnt shut power down) and the reading went down to ~100millivolts. still very hot to the touch. the tempature was around 50 degrees warmer than the ambient tempature so im a little worried about this and hopefully we can go back and fix it.

and yes i have voltage rated tools and voltage rated gloves.

 

[mxslick]

Retightening the loose terminations was a good idea, but if they were already damaged or oxidized from the heat, you will have to trim the wire back to good clean copper (or aluminum) and replace the lugs to avoid a repeat performance.

I do not recommend cleaning the lugs as it may not work and may remove any protective plating, making a bad connection worse. And I think, as debated in another thread, it will void the UL listing.

 

[ptonsparky]

I believe you are on the right track, poor connections. Pull the fuseholder remove the fuses & check the temper of the fuse clips by gently squeezing them. I try to save a few old pullouts for temporary repairs or those that truly can not afford panel upgrades.

I have noticed that certain brands of fuses run hotter than others. When making fop measurements you have to be careful about making sure that both the current and fuses are the same. A fuse that runs at a lower temperature may buy them some time until repairs can be made. There is a difference between the $0.99 NON and a $2.79 time delay

 

[JohnJ0906]

i have a fluke 117 works pretty well.

I have a Fluke 87 that works very well.

Thank you both.

 

[electricalperson]

Retightening the loose terminations was a good idea, but if they were already damaged or oxidized from the heat, you will have to trim the wire back to good clean copper (or aluminum) and replace the lugs to avoid a repeat performance.

I do not recommend cleaning the lugs as it may not work and may remove any protective plating, making a bad connection worse. And I think, as debated in another thread, it will void the UL listing.

the actual connections were fine (didnt have any sign of oxidation) the problem was inside or behind the fuse pull out since that was where the heat was coming from. the metal handle of the pullout was hot as hell