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What is causing this breaker to melt?

WillieWonka's picture

Scenario: 200amp panel (brand unknown) with a 125 amp subpanel located elsewhere. The sub is protected by 125amp brkr in the main.


The 125 amp brkr in the main keeps overheating and starts to show signs of melting. It was replaced with a new due to suspected malfunctioning brkr. The new is repeating the problem. There is only about 60 to 80 amps pulling on the sub at any one time.


Never seen this before, would be interested in anyones opinions???


Edited 1/15/2004 10:54:25 AM ET by Pyroman

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #59693, reply #1 of 20)

It was replaced with a new due to suspected malfunctioning brkr.


Who did this?  Was any additional trouble shooting done?


There is only about 60 to 80 amps pulling on the sub at any one time.


How do you know this?


There's got to be a load of more than 125 amps somewhere.  I'm sure the pros will chime in with more.


Edited 1/15/2004 11:15:20 AM ET by johnnyd

(post #59693, reply #3 of 20)

I've  not seen this personally,....yet.  A friend of mine who knew I worked with electric in homes a lot inquired that his son is having this problem. What is on the sub is a heat pump and an air handler and condenser for AC.


My friend is the one who switched out the breaker with a new one.


As for their being a load greater than 125 somewhere....I'm not opposed to that, but to have two breakers not trip due to it?? What are the odds of that?

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #59693, reply #2 of 20)

What kind of load is on that sub? While you might be measuring 80 amps now, there might be some combination of equipment that is a lot larger load.

Is the breaker ever tripping?

There might be a completely different problem. If you have a bad connection to the bus bar or load terminals it will cause the breaker to heat up at normal loads. Since the breaker was just replaced I doubt the load connects are probably OK, but verify them.

Have you looked at the bus bar?

Since brand is unknow I wonder if there might be a compatiblity problem and the breaker is not seating properly.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #59693, reply #4 of 20)

The breaker never trips. Load on the sub is a heat pump and AC condensor and hair handler.


I'll prob wind up looking at this but wanted to be more knowledgable before doing so. Have not looked at the busses yet.

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #59693, reply #5 of 20)

I have learned LOTs from you and others.  Just finished rough-in, including wiring the panels.  Inspection tomorrow.


So, when and if you have time, for my (and others who read this forum) knowledge:


There might be a completely different problem. If you have a bad connection to the bus bar or load terminals it will cause the breaker to heat up at normal loads. Since the breaker was just replaced I doubt the load connects are probably OK, but verify them.


Why does a bad connection cause the breaker to heat up at normal loads?


Edited 1/15/2004 2:29:12 PM ET by johnnyd

(post #59693, reply #6 of 20)

Current flowing through any resistance will generate heat.

Even wiring will generate heat that is what is behind the sizing charts and the requirements to derate wire in you have over 3 current carrying wires in a bundle or conduit.

A bad connection will cause much more heat to be generated. In this case it might either be the connect of the load wires to the breaker or the connection of the breaker to the bus bar.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #59693, reply #7 of 20)

> Why does a bad connection cause the breaker to heat up at normal loads?



The bad connection will have a significant amount of resistance.  With a lot of current, like 80 amps, you'll get a significant voltage drop across that resistance.  That voltage times 80 amps gives you the number of watts that are being turned into heat at that connection.  That heat is what's melting the breakers. 


With stab-in breaker panels, once you get a burned place on the buss bar, any breaker you put there will potentially have a resistance problem.  If that turns out to be the cause of your problem (and I think it's a good bet that it is), then the way out is to put a new breaker in a different place in the panel. 


 


-- J.S.


 

 

 

-- J.S.

 

(post #59693, reply #9 of 20)

Hope that it is not a Federal box and breakers. As Bill and John said sound like a bad connection at the bus, but Federal breakers have been known to do the same thing from internal faults.


Dave

(post #59693, reply #15 of 20)

Oh I know about Federals....man I've seen them at their WORST. Just one example of that I arrived just in time once to swap one out just right when it started to melt the main brkr. Thing was so hot I killed it at the meter, did my outside work for a while before messing with the panel to let it cool down. The plastic brkr casing was an oozy liquid mess prior to cooling. Then part of it as it cooled molded around some of the internal components. I also did a Federal once where the dang brkrs wouldn't trip for a dime.  No wonder they lost their UL rating and are fire traps.

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #59693, reply #13 of 20)

John, can some type of cleaner be used to clean the bus contact to restore the positive connection? Or once burned always burned?

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #59693, reply #18 of 20)

> John, can some type of cleaner be used to clean the bus contact to restore the positive connection? Or once burned always burned?


Unfortunately, when these things heat up , they usually arc, like an arc welder.  The main difference is that they don't often weld the pieces together.  But the arcing does melt some metal on the buss bar, changing its dimensions. 


In a pinch you might try to clean the bad position by killing the power, pulling some adjacent breakers to make room for your hand, and going after it with scotchbrite or very fine sandpaper.  Look at how the breaker engages the bar, and be sure to get the surfaces that make the actual contact absolutely shiny bright.  If that makes it look ok, swap some very lightly loaded circuits to that position, and keep an eye on it.  (While you're at it, you might take a few minutes to pop all the breakers out and inspect everything.)


But that's only worth doing if the panel is completely stuffed and you don't have the option of leaving the bad hole empty.  When you put in a new panel, it's a good idea not to cut the wires down to the bare minimum, but rather to leave some room for the person who in the future may need to shuffle things around for this very reason.  If you're in the position of having to keep an eye on a bad place in a fully stuffed panel, start planning on swapping it out for a bigger better box.  That way you can do the job on a bright Saturday morining of your choosing.


 


-- J.S.


 


Edited 1/16/2004 2:57:06 PM ET by JOHN_SPRUNG

 

 

-- J.S.

 

(post #59693, reply #20 of 20)

Thanks,  John for all that very good information, appreciated beyond words. I'm guilty of not allowing a lot of excess wire in the panel to move things around. I like to  be neat and pro looking without a lot of wire hanging arouind the panel if you know what I mean. But this situation shows me the value in doing so and will take that into consideration for future panel jobs which starting this Spring I know I'll get....Spring is a time I get a lot of request for swap outs.

If at first you don't succeed, try using the RIGHT tool the next time.  -ME

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #59693, reply #8 of 20)

What brand is it? The Main and the new breaker.  Are the wires stripped correctly, inserted into the lugs and tighted correctly?  What kind of wire is between the breaker and the sub. Copper? Aluminium? Size of the wire?


Possible sources of the heat include;


-bad contact bw bus and breaker in  main panel (Old or dirty equipment)


-bad contact on load lugs of breaker( not tight, corroded wire, insulation not stripped back far enough)


-Wrong size wire from breaker to the sub.


-harmonics(you don't want to go there)


-breaker (internally it could be bad)


 


I once replaced a bad switch and the new one  happened to be bad right out of the box.  That took a while to figure out since you don't expect it.


My supplier told me a story about a customer who replaced all the lamps(bulbs) in the stairways of an apartment building only to find out that he was sold an entire case of bad bulbs.


My company was sold an entire pallet of romex that was manufactured (in error) without a ground wire.  Much of it was installed before the defect was discovered.  (Half of it was stolen in a jobsite theft, serves the bastards right.)


 

(post #59693, reply #14 of 20)

I guess it could be a bad brkr again, would be unusual though.


I'll get the other info and post once I have it. I've yet to visually inspect yet. But I understand your points well.


As for harmonics? Yeah....right, man....you be smoking something to believe THAT is a factor :) LOL


Loved your romex story...yeah, serves them right. Then again, if they're thieves, chances are they won't care about the NEC either, eh?

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #59693, reply #10 of 20)

First Check the connection of both the neutral and the ground. Had similar problem with a panel last fall. Neutral was damaged by the electrician cutting too much wire from the neutral when he was striping off the outer jacket to the wire. Had to replace all breakers just to be safe.

(post #59693, reply #11 of 20)

I've been there on this type of problem. New breaker did not solve because for whatever reason the initial breaker caused arcing at the buss which left that section of the buss burned and pitted. Had to abandon that particular slot to rectify the problem.

(post #59693, reply #12 of 20)

Have to agree to move locations.


Had a commander panel with a screw down double 30 for a dryer break on the bus bar so that the 120 still ran.  Heat would kick on and off and then throw the breaker. It was when the smell of hot plastic hit the wife's nose that the face of the panel came off to expose a blackened bar. Nothing is going back in that spot again just in case.


Scott T.

(post #59693, reply #16 of 20)

Wow, I've never encountered that before. VEry good info to know. I'd never have known that, even if I saw it on the bus I'd likely have thought it'd still be ok. WEll one thing is for sure...glad to know you guys and glad to still be learning.

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #59693, reply #17 of 20)

Dumb qestion. Is the wire feeding the subpanel the right size?

Who Dares Wins.

            

 

   

(post #59693, reply #19 of 20)

Dumb qestion. Is the wire feeding the subpanel the right size?


Gunner, don't know. Now I won't know. The HO called another electrician because they were too worried and couldn't wait for me to get out there. AS to the cause the electrician stated? Unknown as I was unable to speak to the HO yet personally.


Oh well, I did learn something from all of ya so it did make for an interesting question nonetheless.


If at first you don't succeed, try using the RIGHT tool the next time.  -ME
If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME