Circuit Breaker Excessive Heating

[hooverdale]

Hello Everyone,

We have panel board used for commercial purpose with 100A 3Phase 440V main breaker Model GE TCD134100WL, size of main feeder is 30mm2 THHN.

Loads: Lighting and Outlet, Aircon, CCTV.

Power Supply : 440V, 3Phase, 4Wire

No voltage imbalance.230V single phase load used line to neutral.

During full operation, we measured a phase current of 50-65A and the main breaker becomes hot. I doubt if the breaker is overloaded if we only use 65% of its capacity?

The main feeder also getting warmer and it is rated at 115A.

We also measure 6A at neutral conductor (also 30mm2 THHN).

Any thoughts?

Thank you in advance.

 

[DRWeig]

Poor connection of mains cables or the main breaker lugs, or a defective breaker with dirty or misaligned contacts.

How hot does the breaker get? You can look for the hot spot with an infrared imager or infrared spot temperature sensor. Don't forget your personal protective equipment. I would hire a qualified electrician to do the testing, he can also fix it on the spot if it isn't the breaker itself.

Best to you,

Goober Dave

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[hooverdale]

Its like a hot cup of coffee left to cool down for 10mins. Sorry i can't really tell how hot exactly.

We don't have thermal infrared imager or sensor.

Lets say the breaker is not defective nor the main feeder termination and lugs, is it overloading?

We are planning to increase its size to 150A.

 

[jraef]

Current flow involves heat. If you don't know how much heat there is, how can you know if it is "too much"?

There are specific test procedures to determine contact resistance of circuit breakers, but if you don't have access to a thermal scanner, it's doubtful you will have access to the other more specialized instruments necessary. The basic concept is to inject a specifically controlled amount of current through the breaker, usually 300% of rating, and measure the voltage drop across the contacts with a meter capable of measuring millivolts of difference. If you are really worried about it, you can hire a certified testing agency, but honestly on a 100A breaker, you will spend less to change it out.

But you CANNOT change to a 150A breaker unless the conductors are rated to carry 150A!

"Will work for (the memory of) salami"

 

[waross]

I have had bad heating when the bus bar extensions were not tight enough to the bus bars. When you remove the breaker it may become evident where the heat is being generated.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[DRWeig]

Just to provide clarification to one of your questions:

A 100A breaker is not overloaded with 65A current. Not even close.

The incoming feeder gets warm because it's hooked to the source of heating that is undetermined. Heat travels mighty speedy up copper or aluminum conductors.

I like what Bill said -- pop that breaker out and look for discoloration.

Again, DO NOT change to a bigger breaker. You've given no indication that the panel bus is rated anything other than 100A. Oversized breaker + extended overload = fire.

Best to you,

Goober Dave

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[mlhspike]

You should get a Infrared scan done to determine its its the breaker, connections or something else. Then you can be sure to repair the problem.

 

[hooverdale]

Hi everyone.

Sorry for the late feedback. We tested it again running in full load and got 62A.

And we found out that one of the sub-breaker is also heating up. It's a 30A, 3Pole, 440V used for one of the ACU, measured 15A.

We used a temperature laser gun to measure exact temp.

Here's the result for the Main and Sub-breaker (almost the same):

Front of the Breaker: 32deg C
Side of the Breaker: 45 deg C

Room where the panel is located is air-conditioned.

On Monday, the supplier will check it and said they will bring replacement:

In any case that the heating still exist once replaced, what should be causing it to heat?

 

[waross]

Reread the thread.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

You say something is running hot and then you say it is merely 45C. Well, which is it? Certainly can't be both. Start to worry if it exceeds 75C.