Is there such a thing as a weak breaker

Peter Furrow

We’re not born humble, we’re born to be humbled
Location
Cape canaveral Fl
Occupation
Electrical contractor
Periodically I get calls from homeowners that say, “I have a weak breaker that keeps tripping”. First thing that goes through my mind is ground fault, short circuit or overload.
But can a breaker actually be “weak”.
When I say weak I mean trip below it’s ampere rating. From my experience a breaker either works or doesn’t work and there’s no in between. Is that a correct statement?


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nickelec

Senior Member
Location
US
I don't have any data to back this up but I would assume just like everything over time breakers could possibly fail before there rating, damaged contacts excessive on off cycles etc

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480sparky

Senior Member
Location
Iowegia
Being mechanical things built by humans, they're subject to failure. Some might 'fail' and trip at a current level lower than intended. They can also trip at a higher level. But no one ever complains about that because, well, they don't trip. I've never gotten a service call to repair a 'strong' breaker.
 

brantmacga

Senior Member
Location
Georgia
Occupation
Electrical contractor
breakers fail. I've changed several over the years that wouldn't hold anywhere near the trip threshold. I changed a Square D QO250 a couple of weeks ago that would get burning hot to the touch and trip at <10A.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
breakers fail. I've changed several over the years that wouldn't hold anywhere near the trip threshold. I changed a Square D QO250 a couple of weeks ago that would get burning hot to the touch and trip at <10A.
The thermal trip is susceptible to any high contact resistance or other problems within the breaker that generates heat.
The magnetic trip can also trigger below the designed value, but more likely because of mechanical wear on the mechanism or else manufacturing defects. It should be less influenced by reasonable temperature extremes.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Also the breaker itself can be fine but subject to heat from a poorly terminated connection or adjacent devices. Higher temperature means lower trip current.

Jon
 

SSDriver

Senior Member
Location
California
Occupation
Electrician
Yes they can. If all else checks out (solid connections, good wires, etc) then replace the breaker. I have replaced quite a few over the years the trip way below the rated ampacity. I have noticed that most of those breakers were on circuits people were regularly overloading and eventually they wear out.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
Periodically I get calls from homeowners that say, “I have a weak breaker that keeps tripping”. First thing that goes through my mind is ground fault, short circuit or overload.
But can a breaker actually be “weak”.
When I say weak I mean trip below it’s ampere rating. From my experience a breaker either works or doesn’t work and there’s no in between. Is that a correct statement?


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Over my career I've seen, rarely, but often enough to be a pattern, that the basic thermal-magnetic circuit breaker can have a connection point(s) that is(are) in a stage of "glowing". If the heat of a glowing connection is great enough it will trigger the thermal tripping mechanism.

The glowing can occur internally, at the lugs, at the bus connection, or in the next breaker beside the "weak" one. By the time the breaker is misbehaving, there is, in my experience, substantial physical degradation, such as burned up conductor insulation, holes appearing in the molded breaker case, and/or melting or oxidizing of conductor metal.
 

paulengr

Senior Member
The thermal or magnetic element can drift out of calibration and cause nuisance tripping.

It’s more common with motor overload relays.

It is possible but sort of impractical to test small breakers. Usually I just do a functional test. If I say measure 10 A of load in a 15 A breaker and it trips, clearly the.breaker is defective.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
The simplest troubleshooting for a trippy breaker is substitution. Swap it for another one in the panel of equal rating and see if it keeps happening.
 

480sparky

Senior Member
Location
Iowegia
The simplest troubleshooting for a trippy breaker is substitution. Swap it for another one in the panel of equal rating and see if it keeps happening.
If the problem stays with the breaker, it's the breaker. If the problem moves to the other breaker, it's something on the circuit.
 

Another C10

Electrical Contractor 1987 - present
Location
Southern Cal
Occupation
Electrician NEC 2020
This may of been mentioned, I've heard and agree from many in our industry that every time a breaker trips its weakens, maybe only 1/20th of an amp but after 50 trips over 10 years that could derated a breaker by 2.5 Amp or so. Besides the tension in the lever gets sloppy as well.
 

retirede

Senior Member
Location
Illinois
If, say, circuit 25 is the issue, and you swap it with circuit with 27 and 25 keeps tripping, then it's the breaker.

If 27 starts tripping, then it's something in the circuit.
I would say that’s only true if the load profiles of the two circuits are at least somewhat similar.
 

paulengr

Senior Member
This may of been mentioned, I've heard and agree from many in our industry that every time a breaker trips its weakens, maybe only 1/20th of an amp but after 50 trips over 10 years that could derated a breaker by 2.5 Amp or so. Besides the tension in the lever gets sloppy as well.
No. They are tested a certain number of times at their rating (AIC). Essentially the arc breaking mechanism has limited life. Contact top erosion, contaminated arc chutes, that sort of thing. The larger sizes are only tested a few times. Of course if you are tripping at lower current it should last much longer.

This is different from the sensors and hair trigger latch that run continuously when power is on: Springs wear out from metallurgical creep and bearings can seize. Lubricant dries up: Solder joints weaken or solder evaporates. Fasteners can stretch and loosen. All kinds of things happen to trip units that can cause loss of function or loss of calibration.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I don't know if I would call the problem weakening. lots of things can go wrong that cause a circuit breaker not to work properly anymore. A cheap circuit breaker that you suspect has failed can just be replaced for almost nothing compared to the time involved in screwing around with it. If you replace a breaker you suspect might not be functioning properly and the problem goes away you are probably right. If you replace it and the problem continues, it is likely that the problem is associated with the circuit and not the circuit breaker.
 

paulengr

Senior Member
The simplest troubleshooting for a trippy breaker is substitution. Swap it for another one in the panel of equal rating and see if it keeps happening.
So if it goes away is it the breaker or an intermittent issue? So if your computer crashes and you reinstall the software did you fix it? No:

In the US under OSHA this is illegal. You don’t reset breakers until you troubleshoot the cause. NEMA AB-4 has test procedures. UL breakers are only tested say 50 times. Was the last trip number 50 or 10? You don’t know.

If you test the current and determine the breaker is tripping when it should not then you replace or repair. The challenge is a test source but in troubleshooting you use your standard tools. If you find it trips when it shouldn’t based on measurements THEN you replace. My primary injection tester weighs 350 lbs. Nor very portable. But you should already have a good test current in the system.

When a breaker trips it is supposed to be an electrical issue. It is safety equipment. Bad breakers do happen but that should be the last thing you check for and only when you have made measurements and compared your readings to breaker specs can you confirm it’s bad.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
This may of been mentioned, I've heard and agree from many in our industry that every time a breaker trips its weakens, maybe only 1/20th of an amp but after 50 trips over 10 years that could derated a breaker by 2.5 Amp or so. Besides the tension in the lever gets sloppy as well.
The UL and NEMA standards for <100A molded case breakers have them passing hundreds of full load trip and then additional hundreds of no load trips. Then they are tested for to see if they still provide the proper protection.
Barring the fact that you get a breaker on the low side of the performance standards, there is very little you can do to shorten a breaker's lif simply by operating it.
 
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