ECN Forum Forums General Topics of the Trade General Discussion Area 15 amp circuit stumper

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