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Had a call today for a main breaker tripping. It was a Siemens/ITE 200A. I think it was an EQ9685. It was the older vertical handle that looks like two (2) pole breakers with a handle tie across them.

I removed the breaker and the bus looked good and the lugs looked good as well. I removed the lug stabs in the top of the breaker and saw some evidence of heating on one side but nothing real bad.

With that said, after putting it back in and tightening all connections the breaker held but gets hot to the touch on the right side. That's the same side that showed signs of heating on the lug stabs. I don't have an infrared thermometer, but just touching it told me it was too hot.

Only loads on, other than smokes and maybe a light, was the heat pump.
Customer said the heat pump breakers have never tripped, only the main.
The highest amp draw that I saw was 75A with the heat pump on and auxillary heat strips.

Does this sound like a failing breaker? SH didn't have one so I had them order one.
 

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Had a call today for a main breaker tripping. It was a Siemens/ITE 200A. I think it was an EQ9685. It was the older vertical handle that looks like two (2) pole breakers with a handle tie across them.

I removed the breaker and the bus looked good and the lugs looked good as well. I removed the lug stabs in the top of the breaker and saw some evidence of heating on one side but nothing real bad.

With that said, after putting it back in and tightening all connections the breaker held but gets hot to the touch on the right side. That's the same side that showed signs of heating on the lug stabs. I don't have an infrared thermometer, but just touching it told me it was too hot.

Only loads on, other than smokes and maybe a light, was the heat pump.
Customer said the heat pump breakers have never tripped, only the main.
The highest amp draw that I saw was 75A with the heat pump on and auxillary heat strips.

Does this sound like a failing breaker? SH didn't have one so I had them order one.
If the load is close to balanced the breaker is toast.
 

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Could have hit up HD or Lowes for a panel that has the same breaker sometimes the panel is just as cheap as the breaker.
 

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Those ones crap out a lot. If it's hot there's a high resistance connection at one of the internal contacts. You can verify by testing millivoltage drop from line to load on each pole under load. If one is significantly higher than the others at comparable load amps then it's fried inside.
 

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:thumbsup:
Those ones crap out a lot. If it's hot there's a high resistance connection at one of the internal contacts. You can verify by testing millivoltage drop from line to load on each pole under load. If one is significantly higher than the others at comparable load amps then it's fried inside.
Bingo.
Running breakers in parallel is never a great idea, but they test it and get away with it in order to be cheaper and smaller. They know however that mains in resi applications rarely get used, so there is less chance that opening under load will cause a difference in resistance between the poles. But the down side is that once that breaker trips and a little carbon builds up and changes the resistance between the shared poles, one side will start to carry more than the other and it heats up faster, causing nuisance tripping. Time to replace it, but try to get to the bottom of what might have caused the main to trip in the fist place. If it first happened during a summer brown-out or something when everything was running, then them's the breaks. But if the heat pump occasionally jams on startup or has a failing start cap and it's own breaker is failing to trip, causing the main to trip instead, you have to address that or you will be back out again this summer.
 

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Discussion Starter · #11 ·
Those ones crap out a lot. If it's hot there's a high resistance connection at one of the internal contacts. You can verify by testing millivoltage drop from line to load on each pole under load. If one is significantly higher than the others at comparable load amps then it's fried inside.
:thumbsup:
Bingo.
Running breakers in parallel is never a great idea, but they test it and get away with it in order to be cheaper and smaller. They know however that mains in resi applications rarely get used, so there is less chance that opening under load will cause a difference in resistance between the poles. But the down side is that once that breaker trips and a little carbon builds up and changes the resistance between the shared poles, one side will start to carry more than the other and it heats up faster, causing nuisance tripping. Time to replace it, but try to get to the bottom of what might have caused the main to trip in the fist place. If it first happened during a summer brown-out or something when everything was running, then them's the breaks. But if the heat pump occasionally jams on startup or has a failing start cap and it's own breaker is failing to trip, causing the main to trip instead, you have to address that or you will be back out again this summer.
I had forgotten to say in my OP that I did a FOP (?) across the breaker. On the side that is hot I got a reading of around .450V and the side that is not hot around .125V. If this helps any!
 

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What I would have done.

We are often called by electrical contractors to investigate why fuses are blowing or CBs are tripping. Many times the cause is a high resistance connections resulting in sufficient heat to effect the thermal element in the fuse or CB.

A simple method to isolate the high resistance connection and thus the source of the heat is the Fall of Potential Test Method, commonly referenced to as the FOP test. To perform this test, one simply needs a multimeter with a millivolt scale, and an amp clamp.

There needs to be a load on the device to be tested, preferably a balanced load or close to balanced load. In the case of a fused safety switch (FSS). One would measure current across all three phases, then measure from line to load of one pole/phase of the conductor strands (if exposed) for each pole of the FSS. If one phase has a higher that average millivolt measurement (actually the voltage drop across the device under test). Your next measurement would be from line conductor to line of the fuse, if all readings are close to equal move to the next components of the FSS, in this manner you an isolate the high resistance connection.

With an arranged outage repairs can be implemented and a repair FOP measurement taken to verify repairs.

Our thermographers perform this test as part of their IR Scan to isolate to high resistance issue. As sometimes it is not possible to determine from a picture if the issue is a CB connection to the bus or the CB. Additionally it is not feasible to use a DLRO (Digital Low Resistance Ohm Meter)/ Micro ohm-meter to take measurements on small CBs and FSS due to contact point spacing of the test instruments, so our technicians take pre-repair and post-repair measurement s to verify repairs.


An example we IR’d a 200 amp CB this weekend with 155 amps per phase (average), millivolt readings were 38mv, 91mv and 42 mv. The readings were taken from the bus stabs of the CB, negating any possible issue with the CB to bus connection or conductor termination connector to CB connection. B phase had an issue, when we replace the CB we will do further testing and open the CB to see if visual thermal damage has started.

This test can be performed on single pole CB, or any 3-pole devices, we have used this on 4000 amp bolted pressure switches.

As with any testing of exposed energized parts, all safety cautions must be observed, wearing of PPE, isolating the area to be worked in. One issue we have had over the years is customers taking FLASH photography as we are taking measurements. We no longer permit customers to take photos, without prior notice. This minimizes heart attacks.
 

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How much heat is associated with 33W?
Think of a 40W appliance bulb.

The rule of thumb for conductor resistance is to flag any connection with a value more than 50% higher than what you measured on similar connections.

In your case the pole impedances are 0.0016Ω on the lowest pole, and 0.006Ω on your hot pole, that's an increase of 375%, definitely something to worry about. Besides which, while I can't say how much of that is normal operating impedance, generally speaking I get concerned when I see DC resistance values over a couple hundred micro-ohms and you're way over that.
 
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