Bad breaker or too much load?

[Matt Meiser]

Twice in the past couple weeks I've tripped the 100A breaker that feeds my shop from the house panel. On the first trip, I assumed it was a power outage since we've been having them rather frequently this year. I was home alone and it was light enough out to do some cleaning so I did that for an hour or so then went in the house and noticed a ceiling fan running and found the tripped breaker. After resetting I went back out and resumed work without issue. The second time I went in the house right away and found the breaker itself was almost too hot to touch, and obviously wouldn't reset. After allowing it to cool while I ordered a new breaker (see below), I reset it and resumed work without further issue. Both times, I've been running my 3HP cyclone, using AC (2.5T central AC), lights on, and I've been using a power tool. Its possible the trip occurred on AC startup but I don't know. It was pretty hot out both days it happened and the AC seems like its been on more than off.

The house panel is a Westinghouse (now Cutler Hammer) BR series. The breaker the guy before me installed is a Siemens or GE, forget which and I realized a while back it isn't rated for a CH panel. It been on my list to replace it but I haven't gotten around to it. I've ordered the proper replacement which I expect to get today. The shop panel also has a 100A main breaker. I hadn't thought to check if it was hot when I found the other.

I do plan to stick a clamp on meter on there when I've got the cover off and start up everything to get an idea. But I'm wondering--is it likely that the breaker is the problem or am I just pulling too much through it? I've never noticed a breaker that is hot before which bugs me. If I'm just pulling too much I'll have to start leaving the air off when I'm actually working.

[Paul McGaha]

Matt,

Any idea what was running when it tripped?

100 Amps worth? If not, sounds like a problem with the breaker at the house or the feeder to the subpanel.

Just re-read your post, It sounds like you might have been pretty close load wise.

If you've got a clamp on amp meter, It would be easy enough to turn all that stuff on and amp out the feeder.

PHM

[Dan Hintz]

A hot breaker screams fail to me... they do go bad, sometimes they're bad right out of the box.

[Matt Meiser]

The second time I know I was running the cyclone (22A rated), AC (25A fuses), lighting, (? but I'd guess <20A), and my drill press which has maybe a 1/3HP motor. All of this was on (AC may not have been running) for a while before the breaker tripped. I can't remember for sure what I was doing the first time but know I had the cyclone, AC and lights on. And again, it was after the cyclone had been on for a while.

I definitely plan to check load with a clamp-on meter when I change out the breaker. I suppose one possibility is I have more 110 stuff on one leg than the other.

Edit: Me too Dan--hopefully that's it but I knew it should be changed anyway. The breaker came in today's mail so now I just need to find the time to shut everything down and change it out. The one in the panel is >7 years old because it was there when I moved in. Probably 15 or so from when they built the barn.

[Rod Sheridan]

Matt, I'll buy you a beer if it's not a loose connection on the line or load side of your breaker.........Regards, Rod.

[Steve Southwood]

What is the wire size from panel #1 to panel #2? Also distance?

[Rich Noterman]

Matt,

I had this problem years back , it turned out to be aluminum wire, I change the feed to cooper and with the same breaker and never had a problem again. You may want to check what type of wire was used.

Rich

[bruce buren]

I agree with loose connection, Check all connections, loose connection under load equals heating.

Ive wired many motors and terminals the last 15 yrs at the power plant I work at, and seen alot of burned up connections and terminals due to heating of a loose connection

[Ole Anderson]

Correct me if I am wrong, but don't breakers heat up as they get close to design load, and isn't it the heat generated in a bi-metallic strip at the design load that will trip them, as well as use of a magnetic coil to detect a short circuit? Not to say that Matt may have another issue as he doesn't seem to be near the design amperage. Feel your breakers on a heavily used circuit like your DC and they should feel warm if the load has been on long enough to heat up not just the bimetallic strip, but the rest of the breaker as well.

[Matt Meiser]

Well, I'll be retorting the connections when I change out the breaker. And since the existing breaker is the wrong type, it could very well have a bad connection on the buss in the panel, not to mention the load side. I'm not sure what the feeders are, but I'd guess aluminum on a 100a circuit run to an outbuilding.

I'd rate this as "hot" not "warm".

[Mark Major]

I think Rod is right on with the loose connection at the breaker...have seen it many times albeit most often on the old buss fuses. But I'd tell Rod it was a faulty/worn out breaker just so I could get that beer.


Cheers, Mark.

[Rod Sheridan]

I think Rod is right on with the loose connection at the breaker...have seen it many times albeit most often on the old buss fuses. But I'd tell Rod it was a faulty/worn out breaker just so I could get that beer.


Cheers, Mark.

Mark, I would too, however I'm betting that Matt has more integrity than me..................Regards, Rod.

[Bruce Wrenn]

Wires being aluminum, don't forget the "no-ox."

[Jim Neeley]

Alimonum wire has a much larger thermal expansion coefficient than copper. The resulting deforming of the wire during heating and shrinkage of the wire during cooling has been traced to many house fires. Quite a number of years ago in Alaska aluminum wiring was outlawed and I remember hearing the trend was speading nationwide but I have no idea how far or how fast it went.

As for me, I'd look hard at replacing the aluminum with copper, but YMMV.

Jim Neeley, EE

[Matt Meiser]

Replacing is not an option for the sake of replacing. Its underground to the shop. I'd look at separate service before doing that because it could run from the pole to the shop without tearing up sidewalk, etc.