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Hot Breaker

26K views 42 replies 22 participants last post by  steelersman 
#1 ·
I have a GE panel with a 60 amp breaker feeding an AC unit. While running, the AC unit pulls 17 amps. The breaker gets hot. Very hot. About 180 degrees according to the IR. I looked for loose connections and (I think) all the standard items to check. I put in a new breaker (it worked on TV), and there is no difference.
Yes, the ac runs constantly, it is Florida.

Can anybody think of a good reason for this?
 
#2 ·
180 degrees is damn hot. You'd figure it would trip on thermal. Are you sure it is that hot? Have you put your hand on it? Is the breaker making good contact with the bus? Have you moved the breaker to another spot on the bus? Are the other breakers around it contributing to the heat?
 
#3 · (Edited)
I agree. I think your gun is lying to you. The cheaper guns have a fixed emissivity set at closer to .80, so when you're measuring something that is actually perfectly black, it will read higher than it actually is.
 
#6 ·
InPhase. I moved the breaker, the breakers around it all have less than 5 amp loads. It is hot enough you can't hold your hand on it for more than a minute. It does trip sometimes.

MD. Thanks for that info, I know I can always learn something from you.

Bone. It is a stab in breaker. But the panel is pretty new, I wish that was the issue.

Drsparky. There is a slight variation between the two legs (less than .5 amp, which I attributed to controls being taped off one leg.

All good ideas so far, keep em coming
 
#8 ·
A man could do a fall of potential test between the main lug and the load side lug on that branch breaker to find out if it's a bad stab.
 
#10 ·
I sometimes still use that method when I'm troubleshooting a set of parking lot lights that are sometimes tripping a breaker. I put a fuse in each handhole in a weatherproof lampholder. Temporary troubleshooting measure.
 
#12 ·
I put 15's in parking lot lights. I've never really used the screw-in fuse method for anything else. For control circuits, I use these little 1/8th amp things called "tattle tails".
 
#18 ·
Have you got another Temp probe you can check it with? If it's really that hot you wouldn't be able to touch it for a second without getting burnt( I think you said you could hold it like a min). If you think it's a connection take it out clean them(with the power off) and use some of that connection paste with the ground up metal in it(I am known for my high tech descriptions). If you had a thermal camera it would tell the tale. We don't have one here at our plant but the local Power Co will come and bring theirs if I call. Yeah thats it buy a seven thousand dollar camera for a hundred dollar job.... man I am on top today!:thumbsup:
 
#20 ·
It does not take very much resistance to cause your problem. At 120 volts 17 amps draw equals a circuit resistance of 7.58 ohms. To look at it another way, 2.4 amps per ohm and break it down further a 1/4 ohm of resistance equals .6 amps or 72 watts, that energy must be dissipated as heat in a very small area. This would be more than enough to make the breaker hot.
I assume that you are using a GE breaker and not a “close enough” like a Homeline. Homeline will kill a GE panel by destroying the bus.:thumbsup:
 
#24 ·
Having lunch today at a diner a few towns over. A contractor I work with is doing a small project next to the restaurant, and we happened to be eating lunch at the same time. He told me that a breaker for a sub panel had tripped at the restaurant the last time he had eaten there, and asked me to talk to the owner since I was there. I guess he must have been angling for some free lunches. Whatever. I'm never adverse to a little "hero work", and from what he described it sounded like a easy fix. I told the owner i'd look at and give her an estimate. Here's what I found:

90 Amp 2 pole single phase Siemens breaker in a 2 circuit panel feeding a sub-panel about 50 feet away. The breaker, enclosure and SER cable leaving the panel are hot to the touch. Noticeably so, although all I had to troubleshoot with was a Fluke T5-600, so thermal imaging wasn't possible.

No signs of a loose connection, and while I was there(15 minutes) the load never went above 62 amps on either leg. Voltage slightly low, around 236 but nothing to worry about. As far as I could tell, all the major loads were on in the sub-panel which really only consisted a 230 v a/c unit. Everything else were lights and receptacles.

No FOP test, as I didn't have a DMM with me, no thermal imaging (I don't even own a tool like that) so my best guess was a problem in the breaker. The owner said they had 2 A/C units fed out of that panel originally, but recently had moved one to another panel due to both units tripping the breaker often. Maybe the breaker has been weakened by being overloaded in the past? Anyway, I gave her a price to replace the breaker. If she calls me back I'll take a better meter with me to test things a little more.

I'm a damn fine replacement mechanic. I subscribe to the "throw parts at it" school of troubleshooting. :whistling2:plus, maybe I can get a free lunch with every callback. They have great burgers!:thumbup:
 
#34 ·
What is the useful life expectancy of a breaker operating at 80% rate load? I have 40 year old ITE breakers that are failing due to the contacts burning up. BTW, I'm not referring to pushmatic just standard push on breakers. I certainly appears that 40 years is too long. It makes a good sales point if you are out on a service call and can convince the customer that the breaker and/or panel should be changed due to age.
 
#35 ·
From what I can read of the nameplate, it shows MCA of 33ish, and max breaker of 40. The 60 amp GE feeds a disconnect with the properly sized 40 amp breaker in it. The 40 amp breaker does not get noticeably hot. But it is a Square D, maybe I should cram a Square D breaker in that GE panel?

Or, how bout the old ring terminal screwed right to the bus.:laughing:
 
#37 ·
I have a GE panel with a 60 amp breaker feeding an AC unit. While running, the AC unit pulls 17 amps. The breaker gets hot. Very hot. About 180 degrees according to the IR. I looked for loose connections and (I think) all the standard items to check. I put in a new breaker (it worked on TV), and there is no difference.
Yes, the ac runs constantly, it is Florida.

Can anybody think of a good reason for this?
Here is a crazy idea, how about doing some actual testing? FOP or DLRO across connections and the breaker conatcts.
 
#38 ·
Breakers like that usually cost about $15 bucks. I would try swapping the breaker to see if the next one heats up also. Fwiw if a breaker ever gets water in it (like if it was transported in the back of a pickup truck thru a rain) and is put into service later, that symptom is usually what results.
 
#39 ·
i didnt read rest of the posts just going to post mine real quick (going out for dinner <3)

your breaker has a bad connection inside. do a FOP test with a millivolt meter across the phase. you will measure voltage drop across the contacts. some people go by a number but i like to compare readings to other breakers in the panel.

usually if its over 30 mV it might need to be replaced. i have a gut feeling that you will read somewhere in the hundreds of millivolts.

all thats needed to fix it is replace the breaker and thats it.

loose connections cause heat when the circuit conductors are lightly loaded.

with an infared thermometer 20 degrees above ambient tempature is a heavy load. if you have 50 degrees above ambient that means you have a loose connection.

when you replace make sure you properly torque down the lugs with a torque wrench or torque screwdriver
 
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