ECN Forum Forums General Topics of the Trade General Discussion Area need lighting contactor help

Sparky, I had a similar problem with a similar contactor.

The close coil was burning out, It had voltage all the time when the contactor was not energized.

Same set-up as yours, photo cell to control relay, to contactor.

The problem was a aux contact on the contactor that feeds the close coil. This contact was not opening when the contactor shut off.

But if you change the whole contactor as one unit, I doubt this would be your problem.

Just thought I through it out there, it took 2 close coils to find it, as the aux contact wouldn't stick all the time.

Also, why not cut your loses and install a continous duty contactor?

This is a long shot but ....

Is the dealership owner or one of the techs working on a large welding project after hours? My thought is that they are using the building frame / ground as a work lead and are somehow putting high voltage spikes between the "A" phase and ground. These spikes are then taking out the contactor coils. Like I said, a long shot.

How good is the grounding system? How old are the ground rods? What phase(es) are the exterior neon lighting on? Have you tried powering the contactor coils off of another phase? Do you get a wicked voltage spike as a certain light is turned off? Have any of the lighting panel circuit breakers been replace?

What changed or was added 4 to 5 years ago? New lighting, was the building was sided or painted, did the local utility relined or replace the water or gas mains? Was the pole transformer changed? Anything that would cause or increase a High Voltage spike to the contactor coils? Did the utility upsize the feeds that the pole transformer taps off of? Are there switchable PFC caps in the building or nearby on the poles? Is the building very close to the substation? Is anything else in the building also failing frequently? Do they have phone or computer network data problems?

Larry

You mean it is not that torched neutral right there? The blacken copper? Or it that just a bad pic? You replaced the feeder, but did that nuetral also get changed, or is that penitrox? It looked a little green....
[img]http://www.stopab931.org/jack-miller-012[1].jpg[/img]

The lighting all going on at once in a situation like this in 3-phase wye, if well balanced wont be totally obvious, but the contactor may be taking the inbalance of other phases current. It also may appear to have 120 to ground but under certain load conditions it changes. How about the neutral on the other side?

You have a latching relay (contactor) with a latch and an unlatch coil.

Two things will make any coil burn up.

1. Power to it for too long as DNKL states. Latching coils are designed for intermittant duty operation. Make sure the power to the coil drops out after it's energized.

2. Power to it without the contactor fully engaging, will cause the coil to draw the inrush current for an extended amount of time - not good. Generally caused by mechanical wear of the mechanism, contactor isn't fully pulling in.

Measure the coil current. Take your amprobe, wrap 10 wraps of wire around it, put it in series with the coil and energize the coil under load. Divide the measure by ten and compare the current to the book value.

As a well-maybe, coils do have polarity. Might double check the install. That is either flip it around, or reverse the wires?

Bump....

Sparky, don't let this go into the "lost post pile".

I'd like to know what happened, or what they (GE) found.

GE came out Monday morning and checked out what I had going on. They decided that nothing is wrong with the building electrical system or with my control wiring. They installed a new contactor. I turned power back on to the lighting panel and it instantly smoked.
They now admit that it is a known problem with this contactor. Their solution is to keep sending me new contactors until we get one that works.
I am trying to talk them into a deal on a new set-up so we can eleminate this problem.
Richard

Who's paying your time, GE I hope.

All above suggestions are great and may work.

Have you considered putting a voltage recorder / datalogger in parallel with the contactor coil ?
This may record unusual voltage rises over certain periods of power applied to the coil, which cause the burn outs.

If the contactor bridge banks and the contacts can't seat properly an excess current is drawn through the coil which will result in a burn out, usually the contactor is noisy too under those conditions, sometimes some vaseline will help applied lightly on the moving guide parts.

Check coil neutral with an independant earth tester just in case a poor neutral exists which may shift during different unbalanced loads and cause a higher voltage to be present at the coil, although the datalogger will pick that up too.