ECN Forum Forums General Topics of the Trade General Discussion Area noise from breaker trip unit

Jon does win the prize!!!!! Very good Jon. The 3 pole breaker was on but you are correct it is cooler. The hot breaker was a 40 amp with 13.2 amps for load at the time I took the photo. Millivolt drop across terminals was 168 mv. Last year there were 3 bad breakers in this control cabenit. IEC breakers yuk.
The control cabenit is for a coating machine for eyeglass lenses. It runs 24-7 and coats 50,000 lenses a week.

Great responses, guys!
The millivolt drop test is a no-brainer that I should have tried...oh well, next time it will come to me easier.
It seems obvious that I'll have to find a shut-down opportunity..or some way to parallel the breaker during trip unit replacement??? just to be sure there is no interruption in service. Don't know if there is a way to clamp on to the load side wiring of the breaker with the wires from a parallel arrangement. Never seen it done, and it scares me to think of accidentally crossing my phases...one of those "I know this is hooked up right, but do I really trust my life on what I think I know" kind of situations.
Ah, its not worth the gamble. There has to be a way to shut the computer center down sometime.

Dumb question: You said in the original post that this breaker feeds "some vital UPS equipment and another computer equipment panelboard". I can't tell from that whether the other panelboard is behind the UPS, or is separate from the UPS.

If it's behind the UPS, perhaps you can have the UPS take the load while you change out the trip unit at 2:00 AM Sunday morning?



[This message has been edited by SolarPowered (edited 08-21-2004).]

Wish it were so easy...no, the panelboard is fed from the breaker in question; and the UPS, and other computer equipment, is downstream from the panelboard. I only mentioned the UPS in case there is some remote possibility that its non-linear loading on the feeder breaker is affecting the trip unit. Since no one here has bit on that, I assume that the non-linear loading isn't an issue.

Er, you may have overlooked "Noise may be from high harmonic current in the circuit." above.

Elz, harmonics from non linear loading could be the cause of your noise. If you can get a Fluke 43B power quality analyzer you will be able to see if harmonics is an issue. Rent one if you need to $2,200.00 to purchase.

I just replaced two trip units from Westinghouse (CH) molded case breakers because of the loud wining and sizzle noise on elevator inrush.

Voltage drop was less than 100mV, and nothing on the IR. I used my ultraprobe to pinpoint which breakers were the culprits.

Noise is gone.

Bjarney, I see now your line about the harmonic content. Sorry I didn't notice it earlier. I have comprehension problems when reading from a CRT screen!

I'm sure the UPS equipment is generating all sorts of jagged waveforms, there is no doubt that high harmonics are there. But I wonder if this is destructive, or if it is just an issue of some vibration coming off some component in the trip unit that responds resonantly to the high harmonics.
Will replacing the breaker with like kind actually solve the noise issue, or will it just re-occur with the new breaker? When I was checking this out, the air conditioning equipment associated with the computer loads were not on, so the load was very light..pretty much UPS's and a small transformer fed panel. Perhaps with additional loading the noise gets swamped out, I don't know. Wattsup, did the load distribution on your breaker changeouts change at all for the elevator issue? I suppose, in your case, the load was probably just the elevator drives, and the load was still the same. Any feedback from the supplier or from Westinghouse about why the noise was generated?
Just don't want to spend gobs of time traveling and replacing parts if the noise is just an artifact of the particular design of the Westinghouse breaker.