I was out of town last week, doing a cursory "PM" on a small service for a computer center, and noticed that one breaker's trip unit was making a barely audible sizzling/snapping sound. The current draw was only 20%, and there was no evidence of loose connections or discoloration. Since this breaker fed some vital UPS equipment and another computer equipment panelboard, I didn't want to even THINK about shutting it down to replace the trip unit. BUT, it would be good to know if some noise coming out of a trip unit is at all normal. Anyone have experience with Westinghouse breakers' trip units (in a Cutler Hammer switchboard)making noise?

That sizzling sound is just that, aching away until it gives up the ghost.

Replace it soon, or you'll be doing it later. Maybe the buss work its attached to as well....

 
Elz, these comments are worth every penny you paid for ‘em.

Given that the noise could indicate a serious problem, if it is a molded-case breaker, get the client rep to let you remove the breaker front cover while in service, {it should be removable if having an interchangeable trip} making every reasonable effort not to open the breaker, but very plainly understood that you not be liable if it happens.

If it is a so-called “critical” load, would the client prefer to prepare for a trip while you are there, or at another time when you might be an hour away and him desperately needing to find a fried-breaker replacement—should that be the only damage during unscheduled failure?

I get the “Where’s your dual-redundant everything?” stance when people start demanding immediate and absolute answers, sometimes followed by a “Please show me your scripted contingency plans for loss of power to this system.” and, “You mean to tell me that a single-point failure will cause some sort of operational disruption? Who decided on that brilliant scheme?” [There are financial operations and data centers that spend serious money on equipment and planning—having learned from expensive mistakes.]

If the client won’t buy into your plan, walk away and don’t lose any sleep over it.

Thermal imaging or AC millivolt-drop tests could be made with the breaker in service. Noise may be from high harmonic current in the circuit.

It may be apparent that over the last decades, I have become cynical and impatient with clueless, self-important, dime-a-dozen hotshot, junior-MBA managers that demand supreme, unfaltering NASA-grade reliability from electrical gear that they barely paid Wallmart prices for, particularly under the guise of protecting their precious data of value akin to the Dead Sea scrolls.




[This message has been edited by Bjarney (edited 08-17-2004).]

Don't forget the PPE that is required for this work. A short circuit study and arc-blast/flash calculation will be required to select the proper PPE.
Don

ELZ, I agree with Bjarney, you have a shutdown waiting to happen. If I was to bet on it 2:00AM when you dead tired. Noise out of the trip unit is bad.

I do thermal imaging as part of my job. Find someone in your area to do an infarred scan of the breaker. This is a lot safer than opening the breaker front cover live. I am not saying you can't do this, just infarred is safer and less likey to cause the breaker to trip. Also do the millivolt drop test across the breaker.

Here is a 'picture' CaptAl took with the thermal imaging camera.



This one is dramatic but the camera can find very small problems.

Bob

What is it in the picture? Seems like a control wire terminal strip or something of that sort.

Looks to me like a row of three pole switches or breakers.

Toward the center right there looks like a 3 pole module that is off, and it is cooler than the other.

The wires on the top of the picture go into one of those plastic finger wire ducts.

I am guessing that this is a row of DIN mounted breakers in some bit of equipment, rather than a panelboard.

And it looks like one of the terminals on one of the breakers/switches is in sorry shape.

-Jon

I am pretty sure Al told me it was an enclosure filled with IEC style breakers.



I am sure he will get back to us, we work together.

Bob

I think Jon wins the prize.

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.