External blown fuse indication

[StewG]

This variac is ceiling mounted, motor driven, remotely controlled, 3 ph 480, with 4 banks per phase for current sharing. I always find fuses blown when I have to do maintenance on it, but it is never apparent until it is opened up. In the lastest case, 9 out of 12 were blown. Of course, this puts the entire load on the "surviving" fuse(s) I did install some indicating fuses, but without removing all the safety covers, it doesn't help. Is there a way to install some external failure lamp for each fuse, so it can be seen from floor level at a glance?

 

[zog]

Sure there is, but the real question should be why are all of these fuses blowing?

 

[LarryFine]

Is there a way to install some external failure lamp for each fuse, so it can be seen from floor level at a glance?

Simplest is to place a bulb of appropriate voltage across each fuse.

 

[Jraef]

If you wire a 480V rated neon pilot light across each fuse (line to load), the light will glow when the fuse blows. Neon lamps are fairly dim, it may still be difficult to see them if there is a lot of ambient light up there with the variac. They're cheap though, might be worth a try.

Selecta Switch SL53215-8-BG


Fuse manufacturers often have BFI lamps all set up to attach to the fuse clips of their different size fuses as well. They work on the same basic principal.

 

[StewG]

Sounds like a solution is at hand. Never researched 480v neon bulbs before. The fuses blow because this system is shared with a testing lab and the production line. 60 hp blowers are started up with this variac by starting at low voltages and working upwards with an eye on the current draw. It depends a lot on operator finess and if a fuse blows, they don't know it anyway. The problem which brought this all up was one of the wiper sets set screws loosened and it became misaligned with the other 3 which created an "interesting" sound. Without it, I would never have known any fuses were out.

 

[mxslick]

Sure there is, but the real question should be why are all of these fuses blowing?

Sounds like a solution is at hand. Never researched 480v neon bulbs before. The fuses blow because this system is shared with a testing lab and the production line. 60 hp blowers are started up with this variac by starting at low voltages and working upwards with an eye on the current draw. It depends a lot on operator finess and if a fuse blows, they don't know it anyway. The problem which brought this all up was one of the wiper sets set screws loosened and it became misaligned with the other 3 which created an "interesting" sound. Without it, I would never have known any fuses were out.

Based on the description of this setup and what you found in this last trouble call tells me the most likely cause of the fuses blowing is the wiper brushes are worn and arcing (making intermittent contact) which is making the fuses blow.

Your best bet would be to try to talk the client into replacing this out-of-date setup with a VFD for each blower, controlled with a pot to allow them to ramp up at whatever rate they want to.