Main Breaker Tripping.....opinions welcome

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slipknotbmg

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Hello all, been a while since I've been on here. Good to see questions still being answered and code being debated, lol. Anyhow, I've got a problem @ my house, and being a Comm./industrial guy, I figured I'd throw this out here for some opinions. 100A main keeps tripping @ the pole by the meter, not instantly, only every 4-6 hrs. It seems like only when a large load is running a/c, dryer, 1/2 hr. after a hot shower (WH). So I go outside and the brkr. is very hot to the touch, along w/ the secondary feeders. Go inside, open up the panelboard and the other end of the feeders is cool, and all connections in the panelboard look good I.E. no arcing anywhere, and all the brkr's are cool also. Taking a megger home tonight to check the SE conductors. I'm thinking the insulation has broken down somewhere between the house and the pole, and under larger loads, it faults the breaker. Any opinions would be appreciated.
 
I would first replace your main breaker, but also read out the amp draw before and after. Also check the busbar for pitting or damage. If problem continues, check for overload.
 
I had one that started tripping about 2 years after installed. The connections had to be tightened on the aluminum service entrance wire. You can do it carefully with the right tool if you are confident about that sort of thing.

Recognize that you are touching a live, unfused, circuit.
 
I came across several of these in my time. Most of the time it's a loose connection in the meter box. Again you could just be pulling to many amps on the main. Let us know what you find and good luck.
Jim
 
This is a reach but...

Had a simular situation once, where the main tripped at about 87 amps only in the late afternoon / early evening. The panel was on a west wall and it was a brick house. The neigbor had just cut down a big cottonwood tree.

We made some temporary shade, and the problem went away. However, since he had a 125 amp panel, we replaced the main breaker with a 125 and the SEC to #2 copper. He also raised his fence to 8' high.
 
I will add my $0.02.

I am guessing if it was your SE Cable you would be able to identify the problem by visually inspecting the cable (in other words, hold off on that megger and check the current draw first).
 
If it isn't because of excess ambient temperature due to the hot weather which causes the breaker to derate, I vote for the loose connection on the load end of the breaker. Because the load end connections come essentially off of the TM elements the heat generated by a loose connection quite often will heat the thermal element causing the breaker to trip prematurely.
Loose line end connections generally will not affect the thermal element. However, if the heating is extreme enough the contact springs that hold the moving contacts in the closed position weaken causing the contacts to heat resulting in contact failure
 
Not only loose connections on the load end, but aluminum oxide can cause this problem if water has intruded or insufficient NoAlOx.

Mark
 
slipknotbmg said:
. Taking a megger home tonight to check the SE conductors. I'm thinking the insulation has broken down somewhere between the house and the pole, and under larger loads, it faults the breaker. Any opinions would be appreciated.
Click to expand...

How about an update?
 
main breaker tripping

main breaker tripping

think busman is closest... water intruding, possibly by capillary action through 'water-tite' connector that hadn't been properly sealed. water comes into meter socket, drips down to land on top of main breaker.

check for greyish discoloring where breaker attaches to bus. if you got that, replace breaker. sometimes bus needs to be 'refurbished'.

i use silicone to seal connector. old duct seal has habit of separating from se cable after a while.
 
Well, I meggered the USE and all showed well. I ripped apart the meter and service sw. enclosure, meter wasn't that bad, all connections were tight, no oxidation, nothing. Brk'r enclosure had all connections tight, somewhat dirty, looked like water may have entered but not much.

"think busman is closest... water intruding, possibly by capillary action through 'water-tite' connector that hadn't been properly sealed. water comes into meter socket, drips down to land on top of main breaker.

check for greyish discoloring where breaker attaches to bus. if you got that, replace breaker. sometimes bus needs to be 'refurbished'."

Took current readings and turned on everything in the house, even ran the shower to get the WH going. Total draw was around 70A.The top of the main brkr was discolored, greyish, on the plastic, looked somewhat melted, assuming from the heat, Anyhow I replace the whole enclosure w/ a SQ. D, new brkr. and all and haven't had any prob. since. Thanks guys for all your help.
 
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