This one has me stumped.
Here the situation.

15 amp circuit trips when heater plugged into it. Nothing else on circuit.
Ammeter reads 12.5 amps at breaker.
Same heater runs fine on an other circuit drawing same 12.5 amps

OK, bad breaker you say. Swapped breaker with one beside it in panel. Still trips.
Breaker is not hot. Takes about 5 minutes to trip.
Remove breaker and inspected bus. Looks perfect as does breaker contact.

What to check next?

Breaker panel is only about 15 years old FPE. I installed it and I also installed the circuit so I know where the cable runs exactly.

Don't bitch about FPE panel. We still install them new here in Canada. Very popular brand.

"Swapped breaker with one beside it in panel. Still trips."

My suggestion is to replace the breaker with a brand new one, instead of a used one that may or may not have the same problems.

By change the breaker that is tripping a gfci breaker? Another thing you can do is instead of clamping the load wire, clamp the main line. Does your meter have a max hold feature that changes only when the voltage increases?

Breaker is not GFCI or AFCI. I was clamped right at the breaker. I did use the hold feature and it did not spike high. The high max was 12.55 amps.

Do you think it is possible that more than one breaker could be tripping at the low value?

I guess a new breaker should be next try? Anything else that could possibly cause something like this?

Swap with the breaker you know it works on

Bad cable? Takes 5 minutes to trip,maybe that long to heat up the conductors and find a fault in the insulation.

I'm not surprised that two breakers, possibly from the same batch, both trip at the same value, and no one thinks that FPE has mastered the making of breakers.

Hmm, an FPE that trips early? I thought they usually had the opposite problem

Did you open and check the receptacle you originally had the heater plugged into?

The receptacle has been opened. What type of problem in a receptacle could make a breaker trip at 12.5 amps?

Trying to understand what other than the breaker could be the problem now that I have been think more about this.

Unlike fuses -- which are completely swapped out for new -- a tripped breaker always suffers internal damage - normally trivial -- due to the breaking arc in the fraction of a second that the current is being broken.

After enough age, corrosion, oxidization, and trip-outs the contact surface within the breaker can be diminished enough to provide additional local heating.

When you're taking at 15A breaker to its steady state limit of 12A and then some -- you've lost your margin of error.

Replacing a sick -- quick-tripping breaker -- with an old breaker that fails to trip at all is a blind guessing game. Who says that the non-tripper is functioning correctly?

.....

I'd use a TASCO tester or Meg out the field wiring so as to eliminate concern on that front.

Check for voltage loss at the buss: reducing the voltage at that point feeds heat to the breaker. Sometimes I find voltage drops of 1% or more right at the bussing! This is very common for panels near the ocean.

Provide a new breaker whenever weirdness kicks in. In the field no one has the testing equipment to test such a cheap circuit element.

If you want to study up on all of the ways that a circuit breaker can screw-up get a job with a MAIN breaker testing service.

So,It is possible for a breaker to get 'tired'.

Heat trips breakers. Resistance causes heat. Loose connections cause resistance. Sloppy receptacles are loose connections.
Damaged wire in the circuit could also be causing the resistance and heat. Since the heater works fine on another circuit with different wiring, you need to look beyond the OCPD.

Does a breaker next to this one get warm?

Just thinking there may be some heat transfer from an adjacent Breaker.

Bill

I have not been able to get back there yet. The breaker did not get hot when it tripped.

I think it was Einstein who said that once you've eliminated the possible, then the answer must be the impossible.

Let's back off, and start over.

The first question: is it the circuit of the appliance? I say just replace the appliance, and see if the trouble goes away.

FWIW, I had a similar problem some time ago. While a bad power strip was found, and a bad refrigerator compressor as well, the real culprit was a cracked / broken bussbar.

I think the fact that the heater operated at the same load when plugged into another receptacle pretty much eliminated the appliance as the source of the problem.

As for backing off and starting over, I think the other members that have posted on this thread might some have issues with that.

Well, it'd be a dull world if everyone always agreed with me

I don't think we've eliminated the heater, simply because the problem persists.

This appears to be an intermittant problem; the breaker doesn't seem to trip while the OP is actually there watching things.

What else can be done before you tear apart the service equipment? We can swap breakers with a known good one (done), we can megger the circuit itself, we can replace the device, and we can replace the affected load. If all those prove to be OK, then we're left with the impossible: there's a problem with the service equipment.

In troubleshooting, you can proceed one of two ways; you can start at one end and work your way along, or you can start in the middle and start isolating by halves. In either case, a necessary first step is to cast aside any previous thoughts you had, and start over.

In the examples I mentioned above, the fault occurred at irregular intervals. With the fridge the compressor had to be running; with the power strip, the bad connection seemed related to moving the various wires attached to it around, and with the cracked buss ordinary traffic vibrations influenced the amount of contact vetween the two sections.

Oddly enough, as soon as I remembered the cracked buss a theory explaining the OP's problem presented itself: poor contact on the neutral side would lead to a voltage fluctuation, which would lead to the heater (a pure resistance) drawing more current. I wonder if anything else has suffered from high voltage transients?

The OP never tried a new circuit breaker, he never tried Greg's suggestion of using the breaker that didn't trip the circuit.


Intermittent?.......Not really......It trips on a regular basis.
He was there when the breaker tripped. The OP said "Breaker is not hot. Takes about 5 minutes to trip." in his first post. In his later post, he said "I was clamped right at the breaker. I did use the hold feature and it did not spike high. The high max was 12.55 amps."

What is wrong with this picture?

A circuit-breaker is set to trip at 1.5 (150%) times the stated label current, this is what most of us call I2t (the square of the current multiplied by time)
(Higher current, shorter time)
All non-adjustable circuit breakers are the same, provided they are of the appropriate "curve ratio".

Now, IMO, this breaker should not be tripping until it senses at least 22.5A, on the thermal side of the breaker (as opposed to the magnetic side, that senses gross overloads, which should trip instantly).
I suspect a bad breaker.

I have not been able to return to followup.

some notes to respond to questions.

This is a newly purchased plugin wood stove looking electric heater. Not sure, but I think 1500 watts. Two were actually purchased. The other one runs fine on its circuit. This one runs fine on the other circuit.
The circuit in question has always been a problem with tripping breakers when portable heaters were plugged in.
The receptacle being used is the first device on the circuit. It is about 30 feet of cable from the panel.

When I go back, hopefully this weekend. I will open the receptacle again and inspect the connections. I will move the breaker to a different slot. I will try the breaker from the circuit that holds, instead of the breaker easest to get to.

I think US breakers are only 1.25 times label current, but still, there is no way this one should trip.

Side note: older (H, L and U curve) European breakers have considerably higher values, up to 2.1 times label current, while others (current K) come down to 1.25.

There's a variable trip curve that varies from breaker to breaker. It's a pretty big window since the devices are so simple, and variations in manufacture, ambient temperature, etc, impact the actual trip point. Long-time trip is usually something like 1.0-1.4x with larger tolerances for shorter trips. 5 minutes put it somewhere around 1.4-2.0x current.

Bottom line is that these breakers should NOT be tripping in 5 minutes at 83% the breaker rating.

Just to add to the confusion and maybe an answer.

When I was still in the business, we bought 25 FPE breakers in a pack one time. (Not that I was a big FPE fan) but we had all of them with issues of what we called "weak" performance because they would trip for no apparent reason. We had one that would trip when a toaster was used on the circuit.

We set up a separate FPE test panel in the shop with some big honkin' switchable resisters and a couple of ammeters and found out that there were two reasons the breakers would trip at low loads. The big reason was a bad batch of breakers had the temperature limits for trip current heating set too low when they were manufactured and the other, although a minor issue, was slightly misaligned connection lugs which made a little bit of temperature rise in the breaker.

I think those breakers were manufactured in 2000 or maybe early 2001. I can't remember the date codes exactly but it was somewhere around that time period. I know they were of Chinese origin. Maybe you had some from that same batch.

We replaced all the "weak" breakers with new ones and the problems went away.

Hope that helps you out.

Did you check the element?

Problem solved. It was breaker issue. All the breakers I was swapping with, I tried 2 or 3, had the same date code on them. I tried one with a different code and it holds no problem. It seems that the one batch has a low trip curve.
My theory side was trying to figure out how something on the circuit could cause this when I was measuring only 12.5 amp at the breaker. I couldn't understand how it could be anything but the breaker.
The code on the breakers appears to indicate 1992 which is about right for when the panel was installed.
Just an FYI the heater in question had a rating of 120 volts 1350 watts. Should not be a problem on any 15 amp circuit.

"Two bad parts" is always the hardest thing to fix, if you are swapping. You also point out the problem with mass production, mass mistakes.

You got it, good deal!

For the international types, the definitions (nominal) are pretty clear. Long time trip is 1.45 times label current within an hour for almost all curves (except K I think), and values from 4-8 up to 12-16 times label current within 0.2 seconds for short circuit tripping, depending on the curve.

I emailed Schnieder Electric and they claim that it is working within pararmeters as designed. I should not be using any over 1000 watts on the circuit. The cricuit has a clock radio, a ceiling fan and phone charger on right now with the heater

Here is the exact text from the last email.

This is part of the CSA code. We have to build our products to this code.

If you look at the link below, it talks about your specific question. The following is some of the text from this link:

"The largest electric heater that you should attempt to use on a 120V dedicated circuit is something under 1500 Watts. (1500W/120V = 12.5A)

You should only knowingly load a 15A circuit to 80% of it's capacity (80% of 15A is 12A).

Given that this existing circuit has several outlets on it now, the largest electric heater you should attempt to use is 1000W or less "

http://www.electrical-online.com/heatertrippedbreaker.htm


Re: Case ID : 4852047 Product Technical Inquiries, Schneider Electric




So your saying I shouldn't be able run a plug in common 1500 watt heater on any 15 amp circuit in my house? That I am overloading the circuit. That just doesn't make sense. A 15 amp breaker should hold 15 amp forever without tripping.
The breakers have not been loaded at that for 17 years. This bedroom circuit with receptacles not a permanent installed heater. Most of the time it only has a clock, phone charger and light or two used on it.

At 08:24 AM 1/26/10, you wrote:

Thank you for the information.

The problem is very simple, the breakers are loaded above the rating. These breakers are 80% rated and per code should not be loaded over this. . The maximum continuous load should not exceed 12 A. The breakers have been loaded at more than that for 17 years. When a breaker is loaded over this it is in the trip zone and may or may not trip depending on the ambient temperature length of time the current is there and differences in the breaker.

From the information you have provided, I would say the breakers are working as designed and expected.

Here is an interesting article about that

http://static.schneider-electric.us...Case%20Circuit%20Breakers/0600DB0702.pdf

Whenever i have seen those electric fireplaces the instructions said that the unit should be hooked up to a dedicated circuit.Not sure but even the tags on the cord may make mention of this also.

I use a tasco meter now also as mentioned by telsa.
It will simulate a load showing what voltage is actually available after the load comes on, and shows the voltage drop on the Hot and neutral

They stopped using federal pacific panels in the USA years ago to many house fires.i thought they went out of business. I screwed up on a service call one time you plug something in to the outside recp it would trip the gfi kept thing there something wrong with the ckt. come to find out it was what was being plugged in to the gfi that was bad making it trip christmas lights outside.