intermittent breaker tripping . . .

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brantmacga

brantmacga

Señor Member
Location
Georgia
Occupation
Former Child
figured i'd ask around just to see if there's anything i may have missed . . .

we've had a customer call twice in the past two months about an intermittent circuit breaker tripping.

the circuit includes the refrigerator, a sunroom (receps and lighting), and some hallway lighting.


on the first visit the customer indicated the breaker had tripped at some point during the night for 5 consecutive days before we came out.

i went out and checked the current on the offending circuit and found under normal use it was pulling 3A; this is the fridge and a few lights. Startup current on compressor was 14A (checked w/ min/max). VD = 2% under full load.

i checked all device terminations; everything looked good. circuit resistance was fine also. I also checked every light bulb on all the fixtures in the circuit as i've seen blowing bulbs trip a breaker; they were all working fine.

told them it had to be something in the fridge.



they called again last week except this time said they breaker wouldn't reset.

customer indicated the breaker tripped and after several attempts to reset, they ran an extension cord to the fridge. they had not touched the breaker since.

the customer did not attempt a reset w/ the fridge unplugged. i did, and it work. ran my battery of tests again and everything came out fine.

i checked the compressor for ground leaks and found none, and the relay didn't show any signs of overheating. i'm not an appliance guy so that's as far as i could go with it.


in my opinion there is no problem w/ the premises wiring, but can anyone think of something i overlooked?
 
H

hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
Not sure of the age of the fridge, but most had the little start up relay on the compressor, pushed onto the terminals of the compressor under the wire cover, if the contacts of the startup relay start to go bad, the compressor remains in a lock rotor stage drawing the LRA current, I would say that would be a start, but if the fridge didn't cause a problem being on another circuit when plugged into the extension cord then I would look for something else.

Like is there any outside receptacles on this circuit?

Is there any underground feeds off this circuit?

If any of the above is true and it has rained, it would most likely add up to water getting into the receptacle or bad UF cable under ground?
 
P

PaulWDent

Member
Lamp bulb start-up currents can be high

Lamp bulb start-up currents can be high

A 100-watt lamp can have a cold resistance as low as 16 ohms, so it can pull 8 amps of start-up current; along with the fridge's 14A, that's more than 20A, so that could trip a 20A breaker if it was on a hair trigger. So, if a light was on as well as the fridge when attempting to reset the breaker, that could do it.
Try swapping the breaker with the circuit the extension cord is now plugged into and see what happens
 
George Stolz

George Stolz

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Location
Windsor, CO NEC: 2017
Occupation
Service Manager
PaulWDent said:
A 100-watt lamp can have a cold resistance as low as 16 ohms, so it can pull 8 amps of start-up current; along with the fridge's 14A, that's more than 20A, so that could trip a 20A breaker if it was on a hair trigger. So, if a light was on as well as the fridge when attempting to reset the breaker, that could do it.
Click to expand...
I doubt it. The breaker should allow 6-8 times that on inrush anyway.
 
kwired

kwired

Electron manager
Location
NE Nebraska
PaulWDent said:
A 100-watt lamp can have a cold resistance as low as 16 ohms, so it can pull 8 amps of start-up current; along with the fridge's 14A, that's more than 20A, so that could trip a 20A breaker if it was on a hair trigger. So, if a light was on as well as the fridge when attempting to reset the breaker, that could do it.
Try swapping the breaker with the circuit the extension cord is now plugged into and see what happens
Click to expand...


Current and time are factors in the trip. The 8 amp start up of the 100 watt lamp lasts much shorter time than starting current of a motor, not sure how long but possibly in the millisecond ranges instead of the second ranges.
 
I

ike5547

Senior Member
Location
Chico, CA
Occupation
Electrician
Check the connection to the buss stab. Might consider changing the breaker regardless.
 
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cowboyjwc

cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
I had a similar problem one time. Got to where the breaker wouldn't reset so I finally figured that was it and replaced it. A couple of days later I get the call again.

Long story short finally found a roof jack with the pipe cut off but not sealed and it went down into a switch box. It had been raining and the water would drip down the pipe. A little Henry's in the pipe and problem solved.
 
mxslick

mxslick

Senior Member
Location
SE Idaho
Either fridge is going bad, or since the trip is happening at night it can be a sag/surge caused by POCO switching. For some time here I had my UPS' beeping at 1am every night, found out later that the POCO's transformer in the substation had a bad tapchanger switch that kept dropping the load every time it switched.

A momentary interruption while the fridge is running will case the compressor to go locked rotor which can trip a breaker.
 
readydave8

readydave8

re member
Location
Clarkesville, Georgia
Occupation
electrician
A similiar problem a few years ago turned out to be a short in a romex where someone had bent a nail over it. I think heat and cold made the wires move enough to sometimes make contact. It would never do it when I was there.

Another time it was a staple driven too tight causing the intermittent short.

And a nail drove thru and barely touching.

Have seen this more than once.

I don't have a megger but maybe should get one.
 
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