Main Breaker Hot

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GerryB

Senior Member
I went to a HO today whose main tripped a couple times in the last few weeks. It's a newer (3 yr old) 100amp GE 32ckt panel. She said it was hot and smelled last time it tripped, she turned it off, let it cool, turned it back on and it was ok.
It was cool when I checked it today. The conductors were not loose but I was able to tighten 1 turn. I was able to remove the breaker and physically it looks good.
Two things: She said it happens when the dryer is on. So we ran the dryer about 10 minutes, nothing heated up, I read 27-29 amps on the legs before they dropped to about 6.
The other thing, the strain relief is broken at the attachment point, so the service conductors are pulling directly on the crimps to the service entrance conductors. (I told her call the POCO and have them fix that)
So I don't know if one of those things could cause the main to heat up or if the breaker is bad itself.
She hasn't had any other problems that you would associate with the main power coming in.
She will be doing laundry tomorrow and checking the breaker periodically.
Any ideas? Thanks
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
The two most likely causes of breaker overheating are a low but persistent overcurrent and bad connections (either wire or stab for branch/feeder breakers.)
A persistent overcurrent will eventually trip the breaker without damaging it or causing a burnt wire smell. A bad connection will heat the interior of the breaker mechanism and trip it but will get the terminal and wire a lot hotter first.
Since you could tighten the screws a full turn (did you use a torque driver?) chances are very good that it was a bad connection.
Pulling the wires and inspecting and cleaning them would be a very good idea, especially if any insulation damage can be seen. But that would require coordinating with POCO to pull the meter, since you do not want to work with hot service conductors.
 

Martin B

Member
Location
Nebraska
Many years ago, I spent an entire day trying to figure out a similar problem. I don't remember if it was the main breaker or just the branch circuit breaker. The prob. ended up being a crocpot that the H.O had plugged in. My boss was pissed. Any way, maybe there is something wrong with the Dryer???
 

templdl

Senior Member
Location
Wisconsin
I went to a HO today whose main tripped a couple times in the last few weeks. It's a newer (3 yr old) 100amp GE 32ckt panel. She said it was hot and smelled last time it tripped, she turned it off, let it cool, turned it back on and it was ok.
It was cool when I checked it today. The conductors were not loose but I was able to tighten 1 turn. I was able to remove the breaker and physically it looks good.
Two things: She said it happens when the dryer is on. So we ran the dryer about 10 minutes, nothing heated up, I read 27-29 amps on the legs before they dropped to about 6.
The other thing, the strain relief is broken at the attachment point, so the service conductors are pulling directly on the crimps to the service entrance conductors. (I told her call the POCO and have them fix that)
So I don't know if one of those things could cause the main to heat up or if the breaker is bad itself.
She hasn't had any other problems that you would associate with the main power coming in.
She will be doing laundry tomorrow and checking the breaker periodically.
Any ideas? Thanks

I think you may be in agreement that most homeowner breaker may never be turned on and off unless they trip automatically or should it be necessary for a circuit maintenance or modification such as installing replacement switches, fixectures, etc.
When breasker's are never operated I have found it a possibility for the contacts to corrode which results in contact resistance. Resistance equasls hearing, the heating ofted causes the breaker to derate and nuisance trip. The heast casn casuse the spring tty hat holds the moving contact against the stationary contact to weaken resulting in less contact pressure increasing contact heating.
You may use a voltmeter to measure the lline to load voltage for each pole for a voltage drop knowing that voltage drop relates to contact resistance.
I would recommend as a temporary fix to exercise the breaker many times by turning it on and off. When the contacts are opened and closed tty he moving contact actually rubs at the stationary contact which should reduce contact resistance. After doing so remeasure the poles for voltage drop remembering that loading the breaker would increase the voltage drop.
As the breaker is exercised it should be expected that contact resistance is reduced. BUT, never the less this is to be considered a temporary fix only and as such a replacement breaker should be ordered as a replacement.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
The two most likely causes of breaker overheating are a low but persistent overcurrent and bad connections (either wire or stab for branch/feeder breakers.)
A persistent overcurrent will eventually trip the breaker without damaging it or causing a burnt wire smell. A bad connection will heat the interior of the breaker mechanism and trip it but will get the terminal and wire a lot hotter first.
Makes sense. I agree.
Since you could tighten the screws a full turn (did you use a torque driver?) chances are very good that it was a bad connection.
I am disagreeing here. Full disclosure, I rarely use a torque wrench or screwdriver, but based on the few times I have used them I could always get at least a half turn to full turn or more on anything torqued to spec without getting anywhere close to a white knuckle grip. (Why did I do this? Because my boss told me to.) Furthermore, I have never seen an existing main breaker connection that I could not tighten down more after it had been in service for a while.
Pulling the wires and inspecting and cleaning them would be a very good idea,
Good idea.
especially if any insulation damage can be seen.
Good chance when this happens the lug and the end of the conductor are ruined. At a minimum the conductor needs to be trimmed back to some fresh metal.
 

sparkyrick

Senior Member
Location
Appleton, Wi
If the main tripped, I would look for loose connections at the main and the bolted connections to the panel bussing. My next suspicion would be the mains internal contacts. Possibly bad or corroded internal contacts, creating enough heat to trip the breaker. Is there any sign of water intrusion down the conductors to the main breaker? Do you have a thermal camera or IR thermometer? You could check the main with the dryer running for awhile and note any temperature increase of the main.
 

kwired

Electron manager
Location
NE Nebraska
Don't just run the dryer, load that thing up by turning on other loads. Even bring electric heaters with you if there isn't existing heavy loads in the house. The more load you put through a failing connection the faster it will show itself. The dryer only may take hours to get to trip conditions, double the load and you may get some more obvious conditions in 5 or 10 minutes.

You also have to remember when the dryer reaches it's set point temp it will turn the heat elements off until it is cooled enough to call for heat again. So running an empty dryer will heat up quickly and begin to cycle the heat, where one full of wet clothes will take more time to heat up.
 

JFletcher

Senior Member
Location
Williamsburg, VA
Is the HO sure the smell is from the panel and not the dryer? What other loads are on the panel? Baseboard heat, water heater, well pump? I do laundry more than 1x a week; maybe other loads were before, and the dryer was the 'last straw'? Is this a main or sub-panel?
 

GerryB

Senior Member
Hot Main update

Hot Main update

I just talked to the HO and she did laundry all day and the breaker didn't even get warm as she periodically checked it. That's good as I didn't think of the fact that kwired mentioned about with a load of laundry it will be heating for a longer period of time. The other day it cycled down to 5amps from 29 pretty quick.
As I said I removed the breaker (We are allowed to pull the meter around here for a repair) and inspected it, put it back and landed the cables, which also looked fine, newer #2 alum. I also have never used a torque wrench or screwdriver for 100 and 200 amp services, just by feel.
Like I also said before I did anything I tugged on the wires to see if they moved or arced, nothing even though I could get a turn on them. So I'm not sure if removing it and playing with it fixed it or not, we'll see. I had a similar (now that I think of it, also a 100a GE breaker) situation where after thinking it was ok I had a callback and had to change it.
 

meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
Absolutely...make sure the POCO fixes the strain relief, because the conductor holding up the service drop is the neutral (usually ACSR) and if it pulls the splice loose, bad things will likely happen. Open neutrals are probably the most common cause of damage to customer equipment.
 

Pizza

Senior Member
Location
Minnesota
A chronic problem I use to see with square D QO was the connection at the breaker to the bus bar where it snapped in.

One time I had a dryer circuit that kept tripping. I pulled the breaker out to replace it and the metal tabs that snapped on to the bus bar burnt my hand.

Breakers will get super warm if that connection is bad, but will still draw normal operating amps.


Sent from my iPhone using Tapatalk
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
.l.
Since you could tighten the screws a full turn (did you use a torque driver?) chances are very good that it was a bad connection.
Pulling the wires and inspecting and cleaning them would be a very good idea, especially if any insulation damage can be seen. But that would require coordinating with POCO to pull the meter, since you do not want to work with hot service conductors.
I fully agree. Inspecting and cleaning the conductors is almost a must-do after potential over heating.

Makes sense. I agree.
I am disagreeing here. Full disclosure, I rarely use a torque wrench or screwdriver, but based on the few times I have used them I could always get at least a half turn to full turn or more on anything torqued to spec without getting anywhere close to a white knuckle grip. (Why did I do this? Because my boss told me to.) ...
Just my opinion on the issue. Just because you can continue tightening does not mean that you should and doesnt mean it wasnt at the correct tightness. The torque specs are not just a minimum, they are often a maximum as well. Over tightening a lug can deform the conductors to where they are no longer making as much contact, and put mechanical stress on the lug itself which will lead to cracking and failure or stripping of the screw threads. Most lug manufacturers will give you information on the dangers of over tightening their lugs.

http://m.ecmweb.com/contractor/do-you-have-calibrated-arm
http://iaeimagazine.org/magazine/2015/01/15/inspecting-electrical-connections-for-proper-torque/
 
Last edited:

kwired

Electron manager
Location
NE Nebraska
A chronic problem I use to see with square D QO was the connection at the breaker to the bus bar where it snapped in.

One time I had a dryer circuit that kept tripping. I pulled the breaker out to replace it and the metal tabs that snapped on to the bus bar burnt my hand.

Breakers will get super warm if that connection is bad, but will still draw normal operating amps.


Sent from my iPhone using Tapatalk
Was a common problem with aluminum bus panels from 60's and 70's. Not so much from current designs, which most are tin plated copper. Current 6 and 8 space loadcenters with horizontal bus are aluminum bus but can also get them in optional tin plated copper.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
Just my opinion on the issue. Just because you can continue tightening does not mean that you should and doesnt mean it wasnt at the correct tightness. The torque specs are not just a minimum, they are often a maximum as well. Over tightening a lug can deform the conductors to where they are no longer making as much contact, and put mechanical stress on the lug itself which will lead to cracking and failure or stripping of the screw threads....
You get no argument from me. I was just making the point that it's not unusual to be able to get an extra turn on a screw on a main breaker that has been in service for a while.
 

templdl

Senior Member
Location
Wisconsin
You get no argument from me. I was just making the point that it's not unusual to be able to get an extra turn on a screw on a main breaker that has been in service for a while.

I had always recommended to retorque terrminasls during maintenance but I have also heard the contrary too. Probably the better way is to check to temperature of the termination with an IR device. I have an IR attachment for my Fluke which works will.but it is best to check the terminations under load though to get any worth while results.
Terminations that do heat will expand then contact whern cooled. Such heating an cooling cycling will cause the termination to loosten farther which creates greater heating that may lead to a failure.
 
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