hot breaker

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wankster

Member
Here's the situation: there is a 100 amp 3 phase circuit feeding a 70 amp continous load through #2 conductors. The load is an oven so its either on or off, 0 non continuos load. The conductors are good for 130a and 90 amps is 125% of 70 so the 100 amp breaker should be good to go but it gets hotter than i like. I havent actually measured the temp but it is not comfortable to hold your fingers to it for very long. My breaker house says it's normal but i want a second opinion. The breaker is a GE snap in.
 

sameguy

Senior Member
Location
New York
Occupation
Master Elec./JW retired
You need to take its' temp.. How hot by feel, my be hot for you and not too hot for an other. Have you turned off the breaker pulled it out looked at the stab and buss for color change? Put a meter on it under load to see what it is drawing for real? Turn off all breakers in pan. and metered the incoming to see if it is the same as out going?
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
The (#2) conductors are good for 130a and . . . .
No, they are only good for 115, since we can't load them to their 90C ampacity. But that should still be OK for this load.


It sounds like there is too much resistance within the breaker, and that is what is releasing the heat. I would want to check that the breaker is grabbing the bus stabs with sufficient force to get a good connection.
 

wankster

Member
I have measured the current at about 72 amps. I will check the bus connections after the next cycle and also get a reading of the actual temp when it's running.

Where does it say we cannot use 90* ratings? How did i miss that?:confused:
 

growler

Senior Member
Location
Atlanta,GA
It sounds like there is too much resistance within the breaker, and that is what is releasing the heat. I would want to check that the breaker is grabbing the bus stabs with sufficient force to get a good connection.

Charlie is correct but I have seen breakers get hot just because the terminals for the conductors were not tightened properly.

Feel of the conductors where they leave the breaker and see if one of them is hotter than the others. The odds are against all three connections being bad. Re-tightend them just for the fun of it because a half turn can make a big difference.

If it's an area where there is a lot vibration they may have vibrated loose.
 

wankster

Member
so i checked the breaker and the lugs are definitely tight and the push-in connectors seem to be making good contact. whoever installed it decided to put Noalox on the connections, any chance that stuff is raising the resistance?
 

kwired

Electron manager
Location
NE Nebraska
As has been mentioned how hot is the breaker actually getting? The thermal trip mechanism will produce heat within the breaker and if it is a load that runs continuous or close to it it will get quite warm to the touch. This is seldom ever noticed in residential or light commercial because most loads do not run long enough to see this effect. I will see it occasionally in these occupancies on breakers feeding HVAC loads - because they do run for longer periods of time than most anything else in the panel.

Go to an industrial place and just open the door on a panel full of heavily loaded breakers and sometimes you can feel the radiant heat being given off by them.

If your breaker has not been tripping and if you don't have one pole running hotter than the others then it is likely normal. Loose connections usually just start on one pole and not both or all three at same time.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
The operating handle of a breaker is allowed to be hotter than almost any other part.
I would not be surprised to find a fully loaded breaker as "too hot too touch". Off the top of my head I know it can be close to 110?F.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
An IR imager will help most of us spot that poor connection or hot spot that stands out because we can compare it to adjacent connections on the same device. A lot safer than FOP tests. I believe it takes a bit more training to actually condemn something on temperature alone.
 

wptski

Senior Member
Location
Warren, MI
The operating handle of a breaker is allowed to be hotter than almost any other part.
I would not be surprised to find a fully loaded breaker as "too hot too touch". Off the top of my head I know it can be close to 110?F.
A temperature of 140F is generally considered to be the point at which most "normal" people can't touch more than a few seconds.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Sounds like a good place for an IR imager if you can get hold of one.

All you need is a small IR thermometer.

They cost less than 30 bucks. You just point the device at the breaker and read out the temp on the display. I use one quite a bit.

70 Celsius is 158 F. That's enough to burn you. The last hot breaker I read was 145 F and it was too hot to touch.
 

wankster

Member
So i measured the temp at the face of the breaker and two of the three are reading about 115 and one pole is about 140. The pole thats reading hotter is right next to a floppy old loose 20a breaker that is pulling a constant 6a. I will replace all the old loose breakers and hopefully that will help. The conductor lugs on the 100a 3 pole are reading 115 each so im thinking the extra heat is coming from the loose 20 next to it.
 

wankster

Member
Y
Your floppy old loose breaker should have an elevated temp if that is the cause.

Well, for only carrying 6a at running at about 130 i would say its temp is elevated. Only question is how much is being sucked up from the big load next to it and how much is it adding to the heat itself. Its definitely getting replaced. I'm also considering pinpointing all the big and or continuous loads and seeing if i can seperate them in the panel to keep things running as cool as possible.
 

Finite10

Senior Member
Location
Great NW
I've seen breaker lugs only rated for 40 degrees C. What a waste of ampacity.

Did the bus look charred, or even oxidized/discolored? If there's no loose connection, as you mentioned, then the breaker may be bad. If the thing were operating at the trip level continuously then it makes sense that it's hot.

If the adjacent breaker is 'loose' then I would check the bus too, if it were me.
 
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