Fuse holder melting

[badbozo2315]

Naa, happens all the time with fuseholders. Especially the front facing fuses like on a Blodgett convection oven, or high amp draw heater circuits in dish machines. The designers will spec out a 30 amp fuse on a circuit drawing 29 amps.

 

If everything isn’t perfect, and all surfaces nice and shiny clean, resistance builds up and you got yourself a nice little mini heater there.

 

Pretty common…

[ectofix]

I think you figured it out and fixed it.

 

Fuses and circuit breakers can trip due to faulty, overheating connections.  Not in your case here, but read on…

 

Blown fuses/tripped breakers often leads a TECH to unknowingly go searching for an intermittent short somewhere, only to find NOTHING wrong – since the VOM didn’t indicate that there was a short.  So a new fuse successfully gets the unit going and the TECHheads to other jobs.  THEN…several weeks later, ANOTHER call comes in for the same problem.  The same TECH gets there and finds yet ANOTHER blown fuse.

 

That TECH was me about fifteen years ago.  Yes, I’d learned of that problem while troubleshooting a fused disconnect for W/I freezer’s condenser up on a roof.  With persistence (and not wanting another callback), I hung out monitoring it by letting it run for awhile.  After some time, I did some voltage drop tests across the wires in-n-out across each of the three phases.  One of the legs was dropping nearly a volt through its fuse.  I’d narrowed it down to the specific blade connection within that disconnect box.  So I removed power and felt the temperature of that connection.  It made me YELP with an OUCH! for it being so hot.  UH…I never did that again.

 

So THERE’S why the fuse was blowing!  It’s getting HOT!

 

I bought one of those laser thermometers shortly thereafter.  Used it regularly during PMs to identify possible problems when a visual inspection wasn’t telling me that.  FLIR is all the rave for that sorta thing nowadays.  I recently convinced the boss to order us one for use with our iPhones.

 

Since then, that little lesson has allowed me to resolve many other similar problems.  Funny that…the two licensed electricians in my shop have said that they’d never seen that happen.  WELL…this NON-licensed-electrician guy showed them that it DOES happen.

 

In your situation, obviously it was a bad connection that hadn’t transfer enough heat to the fuse to blow it. Strictly circumstantial.  So as long as you’ve made sure the fuse holder…and connections to it…are good (crimps, lug terminals and such), then you’ve resolved the issue.

 

Those IF-fy  connections.  They can sure lead us on some wild goose chases, no matter how GOOD we think we are.  Finding them leads to some new and self-innovated ways to interpret what our VOM is telling us.  I was JUST in one of those HUNTS for the problem on Monday over a meager little IF-fy 12vdc power problem in one of our Hobart flight dish machines.  I caught it and fixed it though.

[olivero]

Yeah, after having battled poor connections for years I started using a 2 flame storm lighter as my pocket lighter, and I use it to solder wires

 

Works like a charm, its a million times faster, no plug in and waiting, just line em up, put the heat on em, solder em up and cap em, tape it. Done deal, best connection and you avoid these annoying problems.

 

I have had contactors melt contacts out and all kinds of stuff, last week I got a serious scare, a high limit, resetable tripped on a  unit. I seen it before, poor connection once again, saw it on another unit and fixed it by soldering it but this time, OH BUT THIS TIME, it was different. Soldered it up and reset it. Turned it on and I shit you not, the ceramic looked like 2 light bulbs went on inside of it. First thought, wow that;s strange, 2nd thought, looks like a an arc fault, 3rd though,t, probably is an arc fault, wow never seen that and BOOM ceramic went poof and as a welder, I hear arcs all the time and I am used to it but this was like when you pull your electrode waaaay too far off the piece and the arc just screams, never reached a plug so fast before. Power of loose connections is insane, the amount of things that can happen is just incredible.

 

So yeah, definetley know the shitty connections, just figured the fancy german high tech special order fuse holder would be better than that but I guess in the end, its just one wire through a fuse to another no matter how you do it.

 

Thanks for the answers guys, just wanted to make sure I was not seeing something extraodinary, seen other types of holders do it but never this type.

 

Once, again, thanks.

[fixbear]

A Fuse is a choke point in a circuit that creates heat. Minor at the fuse’s rated value or flow rate. As the flow of electricity reaches the max value the fuse element gets hotter and melts. Causing it to be what many refer to as blown. Due to this happening at the max flow rate there is a arc that is contained inside the fuse. High value fuses are filled with sand to absorb the high parting arc.

   In the fuse hold described the fuse end is attached to the terminal and transfers heat to it causing oxidation and more heat from the resistance of the wire connector. It wasn’t stated if it had spade terminals, or soldered, but be aware there is a lot of lower priced spade terminals out there that will make the problem worst. They do have different temperature ratings as well as amperage.

   On a related item, I once had a 3 phase motor that the .problem never showed up till I put a line  monitor on the system. They had a phase shift problem in the power grid that would make one leg really low and the other two higher than rated. Always check all three on 3 phase. Power company had replaced one transformer at the sub station with a newer one and the time lag was different. Very rural area and my customer was the only poly phase customer on the line. Every time the kids in the area can home from school it got worse. I fought with the power company for two years before the sent me a ABB oversized motor starter for the whole plant to create a true power supply. The substation is still 4 degrees behind on the “A” phase.

   Hope I haven’t confused anyone.

[olivero]

Interesting stuff. Must have sucked to figure that one out.

 

Connections were the type where you insert a flathead scredriver and “lift” the connecting point and slide your wire in

[fixbear]

That type terminal block is not normally a problem. The spring tension is usually real good. But isn’t it supposed to have a pin terminal on it?

 

In relation to the other item, I had to replace the compressor  (12 Hp Bristol) and a blower wheel (belt driven 10 Hp) from the vibrations and overloaded phase. Was over a 6 year period this evolved. Once the phase rectifier was installed everything smoothed out and quieted down.  FYI, This was a 480 volt system. The VSD was rated for a 40 Hp motor.

[olivero]

Wow, pretty big system.

 

Connection for the fuse is almost like a cap that the fuse inserts into and is then screwed into its holder like that. The wires did not burn or melt anything, it was the chamber the fuse is in.