# Help me troubleshoot main breaker tripping



## just the cowboy (Sep 4, 2013)

Trip curves will let the one with the lower curve trip first almost every-time.
May be the underground has a leak you need a megger to test it.


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## HackWork (Oct 2, 2009)

Changing that 100 amp breaker is a low-cost and easy to do task.

I would go there with a new breaker and have them charge both cars while taking a reading to see how much is actually being drawn.


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## canbug (Dec 31, 2015)

I have a similar problem with a well pump. Maybe use the infrared gun and see if it's running hot?


Tim


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## varmit (Apr 19, 2009)

My first guess would be the underground wire is damaged - especially if it is aluminum. If aluminum wire, that is buried, either in conduit or direct burial, gets even a pin hole in the insulation, the conductor will dissolve from the heating of a high resistance ground fault. I have seen direct burial aluminum conductors with no aluminum, just the remaining insulation for several feet.

Copper can do this also, just not as dramatically as aluminum. 

You need to determine if the breaker is tripping from over current or a ground fault.

And yes, the breaker can be defective, but not as likely as other problems.

Check the voltage, at the 100 amp panel, both with and without a load. If the voltage drops more than 3% to 5% under load, either the wire is questionable or a breaker or connection has a problem at the service.

At the 100 amp panel, heck current on both ungrounded (hot) conductors under load. Both should be really close to the same current if there is no appreciable 120 volt loads. If one of the conductors is damaged, it can limit current.


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## stiffneck (Nov 8, 2015)

Remember, once a breaker has cleared a short circuit, that's it, it's done. However, most of the time people reset, as if it where an overload. Do you know the history of this breaker? You could take it out and send it in for testing, or just do what Hack said and replace it. Either way, breakers are a wear out item and sometimes they just don't work. I prefer fuses myself, but not going to happen for residential.


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## varmit (Apr 19, 2009)

stiffneck said:


> Remember, once a breaker has cleared a short circuit, that's it, it's done. However, most of the time people reset, as if it where an overload. Do you know the history of this breaker? You could take it out and send it in for testing, or just do what Hack said and replace it. Either way, breakers are a wear out item and sometimes they just don't work. I prefer fuses myself, but not going to happen for residential.


Yep, if we could know the history of the things that we repair, it would be a lot easier.


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## NDC (Jan 12, 2016)

stiffneck said:


> Remember, once a breaker has cleared a short circuit, that's it, it's done. However, most of the time people reset, as if it where an overload. Do you know the history of this breaker? You could take it out and send it in for testing, or just do what Hack said and replace it. Either way, breakers are a wear out item and sometimes they just don't work. I prefer fuses myself, but not going to happen for residential.





HackWork said:


> Changing that 100 amp breaker is a low-cost and easy to do task.
> 
> I would go there with a new breaker and have them charge both cars while taking a reading to see how much is actually being drawn.



I replaced the 100A breaker at the shed. It was a stab lock and it was arching when I turned it on under no load and the handle felt sort of weaker to the replacement breakers handle.
If this doesnt solve the issue, Would it be a good idea to re-route the garage feed to a fused 100A disconnect instead of having it fed from the panel?
I will megger the underground wires before doing this though.


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## CoolWill (Jan 5, 2019)

I have it on good authority that main breakers don't trip.


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## Forge Boyz (Nov 7, 2014)

Yesterday I accidentally shorted out a control circuit. It tripped a 15A QO, a 30 2p Siemens and the 100A main on the panel. 

Sent from my SM-G970U1 using Tapatalk


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## dronai (Apr 11, 2011)

Forge Boyz said:


> Yesterday I accidentally shorted out a control circuit. It tripped a 15A QO, a 30 2p Siemens and the 100A main on the panel.
> 
> Sent from my SM-G970U1 using Tapatalk


Did you piss off a bunch of people ?


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## CoolWill (Jan 5, 2019)

Forge Boyz said:


> Yesterday I accidentally shorted out a control circuit. It tripped a 15A QO, a 30 2p Siemens and the 100A main on the panel.
> 
> Sent from my SM-G970U1 using Tapatalk


Pfft... I once caused a short on a 277 V lighting circuit that tripped the GFP on an 8000 amp main and stalled $125000 per day production.... I mean, I'm the only one who knows I initiated the short, because it was obvious the ancient GFP was waaayyyy too sensitive. They just blamed old equipment and contracted with my boss to upgrade that part of the service at the next shutdown:vs_laugh:


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## Forge Boyz (Nov 7, 2014)

dronai said:


> Did you piss off a bunch of people ?


Actually not. It was in a sawmill shut down for maintenance so 1 guys grinder quit and all the lights went out. The worst part was the owner was in the building to see it happen.

Sent from my SM-G970U1 using Tapatalk


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## dronai (Apr 11, 2011)

Forge Boyz said:


> Actually not. It was in a sawmill shut down for maintenance so 1 guys grinder quit and all the lights went out. The worst part was the owner was in the building to see it happen.
> 
> Sent from my SM-G970U1 using Tapatalk



Ahhh the owner ! Been there done that. Shorted a 480V panel with a screw from the dead front went into a 100A wire ! 

It tripped the main to the building, don't remember what amperage that was. Had to climb a fence into the electrical room to reset. With the owner telling me, you are going to ruin the product !!! a giant oven baking ceramics


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## Forge Boyz (Nov 7, 2014)

He was all cool with it. It's just embarrassing to have it happen where people can see it.

Sent from my SM-G970U1 using Tapatalk


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## The_Modifier (Oct 24, 2009)

Forge Boyz said:


> Yesterday I accidentally shorted out a control circuit. It tripped a 15A QO, a 30 2p Siemens and the 100A main on the panel.
> 
> Sent from my SM-G970U1 using Tapatalk


Jezuz- what panel hold both of those breakers? :vs_laugh:


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## Cow (Jan 16, 2008)

Like the others mentioned, we would meg it first. That only takes a few minutes. We fix lots of underground wiring.

If I couldn't draw any conclusions from that or anything else, I would lean towards replacing the 100 amp breaker in the shed. Just for the sake of the cost/benefit ratio. Labor to troubleshoot is expensive, replacing a questionable 100 amp breaker is reasonably inexpensive looking at the big picture.


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## five.five-six (Apr 9, 2013)

Forge Boyz said:


> Yesterday I accidentally shorted out a control circuit. It tripped a 15A QO, a 30 2p Siemens and the 100A main on the panel.
> 
> Sent from my SM-G970U1 using Tapatalk



I don’t even remember what brand meter combo it was but I put a dead front in backwards once, it shorted across the 2 buss bars between the meter and the main breaker. Popped one side of the POCO pole transformer. I walk out to my truck and everyone on the block is standing our front their house looking at my truck wondering why 1/2 of their electricity doesn’t work.

5 star day for me right there, I tell you!


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## NDC (Jan 12, 2016)

I replaced the breaker in the shed feeding the sub panel and it seems to be holding the continuous current. I'm still worried that it's going to trip. Maybe not now but eventually. I just dont trust the stab lock breakers. 

I also meggered the wires and they are fine.
I am thinking of bypassing the panel that feeds the garage and installing a 100a fused disconnect instead. I dont install to many fuses so which brands and type do you recommend that can really do a good job of hold 70 or so amps continuous?


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## HackWork (Oct 2, 2009)

Are you talking about Federal Pacific Stab-Lok? Or just the normal way that all modern breakers stab onto a bus?


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## NDC (Jan 12, 2016)

HackWork said:


> Are you talking about Federal Pacific Stab-Lok? Or just the normal way that all modern breakers stab onto a bus?


 Here they are called Federal Pioneer and yes they are stab-lok type. This is the breaker https://www.homedepot.ca/product/sc...tab-lok-na-plug-on-circuit-breaker/1000110419


I could be wrong but I think stab-lok panels can still be purchased and installed. Why anyone would do so is beyond me. I just don't like the way the breakers stab into the bus, especially 60A and up. Its a struggle getting these breakers in sometime.
So I'm thinking to avoid any future failure of the breaker, I should install a disconnect instead. I could also replace the panel but the cost would be higher. 

The absolute last thing I need is a fuse blowing. At least a homeowner can reset a breaker.
Another option would be to install a 2 circuit 100 amp load center and install a 100 amp breaker, I think Siemens makes one.


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## HackWork (Oct 2, 2009)

Now it makes sense, down here those are very problematic and I understand why you wouldn’t want to continue using that type of breaker for car chargers.

However, adding the fused disconnect sounds like a very roundabout solution.

If it was my job, I would explain to them the problems with the stab lock breaker and give them the option of installing a new one which may burn up again or replacing the panel.


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## NDC (Jan 12, 2016)

HackWork said:


> Now it makes sense, down here those are very problematic and I understand why you wouldn’t want to continue using that type of breaker for car chargers.
> 
> However, adding the fused disconnect sounds like a very roundabout solution.
> 
> If it was my job, I would explain to them the problems with the stab lock breaker and give them the option of installing a new one which may burn up again or replacing the panel.



What do you mean by roundabout solution?


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## NDC (Jan 12, 2016)

I used a Greenlee 5882 megger to test the insulation but I'm thinking I may have missed something. 

The conduit from the shed panel to the garage panel has no ground wire in it and it's pvc conduit. The grounding is done at the garage panel via a ground plate.
I tested line to line, line 1 to neutral, line 2 to neutral. I then tested line 1 and 2 to the ground plate connection.
My testing was done at 500V and all measurements showed up infinite.
Did I miss something? Should I measure at 1000V?


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## HackWork (Oct 2, 2009)

NDC said:


> What do you mean by roundabout solution?


Tapping off the feeder and installing a fused disconnect in a resi application just to avoid using a breaker in the existing panel (when there is space) seems excessive and going to an unnecessary extreme. It seems like a big bandaid. 

The fact that the breaker is burning up due to the bus connection (which is well known as being flawed) should be enough to get them to change out the panel. 

This is one of those jobs that will sell itself. You tell them that the breaker connection is flawed and give them the choice to try a new breaker and see if it's works or have a new panel installed. If they go for the cheaper route of just trying a new breaker, and it fails, then the only thing they can say is "He was right, we need a new panel" and it sold itself for you.


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## HackWork (Oct 2, 2009)

NDC said:


> I used a Greenlee 5882 megger to test the insulation but I'm thinking I may have missed something.
> 
> The conduit from the shed panel to the garage panel has no ground wire in it and it's pvc conduit. The grounding is done at the garage panel via a ground plate.
> I tested line to line, line 1 to neutral, line 2 to neutral. I then tested line 1 and 2 to the ground plate connection.
> ...


Is neutral bonded to ground at the garage panel? Car chargers need a good ground to work, or else they shutdown.


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## NDC (Jan 12, 2016)

HackWork said:


> Tapping off the feeder and installing a fused disconnect in a resi application just to avoid using a breaker in the existing panel (when there is space) seems excessive and going to an unnecessary extreme. It seems like a big bandaid.
> 
> The fact that the breaker is burning up due to the bus connection (which is well known as being flawed) should be enough to get them to change out the panel.
> 
> This is one of those jobs that will sell itself. You tell them that the breaker connection is flawed and give them the choice to try a new breaker and see if it's works or have a new panel installed. If they go for the cheaper route of just trying a new breaker, and it fails, then the only thing they can say is "He was right, we need a new panel" and it sold itself for you.



My only concern with this is if say a Siemens, square d, or cutler is installed and the new 100 amp breaker still trips. I would be happy to install a newer panel but I'd have to be absolutely certain that the new 100 amp breaker will not trip at 60-70 amps load or Im going to look like a complete idiot. I figured fuses can hold a continuous current of 70 amps better than a circuit breaker can but maybe Im wrong.


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## NDC (Jan 12, 2016)

HackWork said:


> Is neutral bonded to ground at the garage panel? Car chargers need a good ground to work, or else they shutdown.


Yup its bonded to ground at the sub in the garage.


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## HackWork (Oct 2, 2009)

NDC said:


> My only concern with this is if say a Siemens, square d, or cutler is installed and the new 100 amp breaker still trips. I would be happy to install a newer panel but I'd have to be absolutely certain that the new 100 amp breaker will not trip at 60-70 amps load or Im going to look like a complete idiot.


 I know exactly what you are saying. However, since the bus connection on the breaker has already burnt up, that displays the fact that there IS an issue with it. Whether it fixes the breaker tripping or not is separate, IMO. Breakers trip all the time from shorts and overloads, the bus connection should not be burnt up.



> I figured fuses can hold a continuous current of 70 amps better than a circuit breaker can but maybe Im wrong.


 I would not count on that. And, like you said, blowing an expensive fuse in a resi situation is not a good idea.


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## eddy current (Feb 28, 2009)

Did you install the new breaker in the same spot that the old one was in? You said you saw some arcing, that tells me the buss is probably damaged and you should not install the new breaker in the same spot.


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## NDC (Jan 12, 2016)

HackWork said:


> NDC said:
> 
> 
> > My only concern with this is if say a Siemens, square d, or cutler is installed and the new 100 amp breaker still trips. I would be happy to install a newer panel but I'd have to be absolutely certain that the new 100 amp breaker will not trip at 60-70 amps load or Im going to look like a complete idiot.
> ...





eddy current said:


> Did you install the new breaker in the same spot that the old one was in? You said you saw some arcing, that tells me the buss is probably damaged and you should not install the new breaker in the same spot.


The arcing I noticed was within the breaker itself, not at the bus. And when I turned it on I made sure that the sub panel main was off so there was no load connected. After replacing the breaker the arcing stopped. I think the steady high current for extended periods of time are going to eat up the new breaker though. Just dont trust this FP breaker.
The bus itself shows no signs of burning.


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