Here's the deal. I have a customer with a 200 amp lighting contactor. 208v 3ph. All 3 phases draw less than 140 amps. First contactor lasted 15 years with no problems. In the last 4 years the coils have burned up 9 times. Twice in the past 7 days.

It has a photo cell controlling a small control relay that powers the coils on the contactor. I have replace all controll wireing, photo cell and relay. I installed new coils this afternoon, tested and watched for about an hour. Everything was OK. Tonight the lights did not come on. Had power to the close coil, but it would not close. I removed all control wires, and manually turned on the contactor. Coils started smoking with no electrical connection to them. Also showed 120 volts to ground on both open and close coil terminals. This was checked with a DMM and A Wiggy.

Any ideas what could cause this?

I don't understand. Your saying that you have a single 200 amp lighting contactor with multiple coils? The contactors I have used only have one coil. I would make sure that the coil is rated for the control voltage as that would surely smoke it. Improper voltage, incorrect wiring, or really cheap quality of coil is all I can come up with.

[This message has been edited by RobbieD (edited 10-02-2006).]

Internal jumper on coil? Pulls power from one of the legs? It's bitten me before.....

Coil voltage?

Does the "new" contactor have an internal jumper between the power feed and the open and close coils?

Does the new contactor only require external contacts to operate?

120 VAC to ground certainly sounds like the coil power comes off of one of the 208 V phases.

I worked on an ASCO lighting contactor with the electricians a few years ago. I seem to remember a cam of sorts that would internally open up the closing coil path once closed, and opening coil path once open. This allowed using one photocell controlled relay with form "c" contacts to control intermittent duty contactor coils. The cam getting messed up could explain letting the smoke out but only with the control ckt connected.

Now I seem to remember ASCO sending us a bunch of 24 volt ATS coils that didn't much like the 120 volt control ckts. Dealing with them is like walking into a room of 400 people, all named Bob. You might recognize him if you see him again but the label on the shirt doesn't help that much.
Joe

RobbieD--1 coil to open, 1 coil to close. 120v coil and 120v control circuit.

Grover and Larry C--Internal jumper for grounded conductor only. Power from A-phase to photo-cell to reversing relay then to contactor. Contactor is a GE. They have been involved in this for the past 3 years and can't figure this one out.

What gets me is the coils smoking tonight after I took ALL control wiring out of the picture. No power to coil, photo-cell, relay at all, and it still showed voltage on the coil. Could the coils be acting like an isolation transformer somehow?
Richard

Lets assume contactor is OK. What changes from day (when you tested it) and night (when it lets out the magic smoke).

Is it possible that the neutral for the lighting circuits shifts under load? This might overvoltage the coil. Perhaps the neutral ground bond is missing? Are the lighting circuits fed from a dedicated transformer? Is there the possibility that one of the lighting circuits is accidentally tied into another power source?

I would suspect that if the factory has been involved and they are coming up blank, then perhaps it is a facility issue.

What is downstrean of this contactor?

LarryC, Contactor feeds a 200 amp lighting panel that feeds all the parking lot lights, pole sign and building exterior neon. This is a car dealership, so quite a bit if lighting. In December of 05, I megged all branch circuits out of this panel and found nothing wrong. I replaced the feeders to this panel at that time also. The only transformers are the pole mounetd utilitys.

I also thought somthing had to be different at night that I wasn't seeing during the day. I have spent hours checking during the night and can find nothing different. I agree it is a facility rather than contactor problem. I will take pics today and post them after work. Maybe you guys will see somthing that I dont.
Thanks, Richard

Richard,

When the lighting panel is energized and under load, what is the voltage between the panel neutral and the chassis frame? I ASSUME that the neutral ground jumper in the panel has been removed.

"When the lighting panel is energized and under load, what is the voltage between the panel neutral and the chassis frame? I ASSUME that the neutral ground jumper in the panel has been removed"

Zero between chassis and neutral and no jumper installed.

The coils can only "smoke" if there is electricity to them, so there must be a wiring error.

Most mechanically held contactor coils are not designed to be "on" all of the time so they have coil clearing contacts. Is there a Normally Open contact in series with the open coil and a Normally Closed contact in series with the close coil?

What is the manufacturer and type of contactor?

I agree with JDB, all of the lighting contactors I have dealt with have coil clearing contacts to prevent just the situation described. Most of my contactor exposure has been Square D, but ASCO, GE & others pretty much use the same scheme of things. Because of the mass of the armature it takes a lot of current to hold in the steel, so as an economy measure(cheaper coils, less energy consumption) they are designed to take the power off the coils as soon as the contactors change state. I would look at the mfg. wiring diagram very closely and not try to rewire them - the ones that I have worked on in dozens of contactor panels, some with 25 or 30 contactors, have the neutral switched as a part of the manufactured assembly. A well meaning electrician in Atoka, OK, rewired a mess of these contactors 'cause the factory wiring was against his principles, and upon energization, smoked several thousand dollars worth of contactors before the store opened, had to replace all the coils...

sparky,

is it a GE360CR? or in that family? We had a similar problem with a 360. Worked fine for about 10-12 yrs, then started to burn up control wires and coils. We actually found several cracks on the magnet and a few other places on the main contactor. It seems that someone had replaced the on of switch with a standard 3 way (leaving continuous power to either the on or off contactor.) that and the daily pounding of drawing in that load, finally did it in. We replaced the unit with the newer model (much smaller and lighter)

Wild-ass guess: "Something different at night": That could be the photocell.

If the photocell results in a continuous application of power to the coil, that might cause it to burn up, as I believe that type of coil is designed to only be pulsed for long enough to switch between the on and off positions.

[This message has been edited by SolarPowered (edited 10-04-2006).]

solar, it is. One of the problems we found with ours was that the 3-way switch was used. Causing the same issue. Constant power.

It's a GE # CR160MC7502A Pics can be seen here http://pg.photos.yahoo.com/ph/sparky_806/album?.dir=6465re2

photo-cell controlls a relay. the relay controls the open/close coils on the contactor. according to my GE rep, everything is correct.
Richard

[This message has been edited by sparky806 (edited 10-04-2006).]

sparky806:

Putting my thinkin' cap on and looking at all the pics, in particular numbers 16 and 18, what I'm seeing is badly pitted/burned contacts (second from left) and serious burning of the moveable pole piece that appears to be pulled in by the action of the coils.

Best guess here is that the burned pole piece is causing chatter (does the contactor buzz even when the coils are disconnected?) which is frying the contacts, causing the smoke.

Try replacing the contact set and the pole piece assembly, (items in pics 16 and 18), I'm willing to bet a case of your favorite beverage that'll fix the problem.

Good luck and keep us posted...

Kind of looks like a 100 Amp Lighting Contactor drawing >100 Amps across the Contacts.

Looks more like an alignment problem is to blame here, which is keeping the Contacts from seating properly when closed.

This would be from installing the Lighting Contactor assembly over a non-flat surface, then tightening everything down - causing the Contactor's back mount plate to be bent; resulting in the Contacts being misaligned (not a solid and full connection) when they are closed and latched in.

Scott35

Ok..... First, you're dealing with a now antiquated contactor design for this application. (Although they still make them) If this were a newer design unit it would have self cleaning /wiping contacts, and for that matter it would be switching loads individualy with a number of smaller relays. Thats a lot of amperage to switch this way. If you're not going to go all the way and just suggest a full upgrade of the contactor, which may require a different panel or enclosure to the side, those contacts are garbage at this point. mxslick's suggestion is a good one, but but unless they make good FAST and SOLID contact in the future this problem will only repeat....
[img]http://us.a2.yahoofs.com/users/43db47d7z80dafa65/6465re2/__sr_/fe69re2.jpg?phg6LJFBKpQ0cf_a[/img]
As a temporary fix to further troubleshoot, take some 400 grit, and then some 600 grit sandpaper to them and polish them up. Then some contact cleaner to get rid of the residue. Put the contactor together and test it with no load outside the panel. And check to see if this thing is operating properly with a smooth solid connction, and that it has good tension on the contacts when closed. It may be that the mechanism is binding....

Now.... It also may be that the 120 you see when it not loaded by the contactor is much less under the load of the contactor. And this might not be enough usable power to actuate the contactor fully. And may be the cause of those arching contacts.... (Also how are the secondary contacts, are they OK?) One cause of this might be what appears to be a loose nuetral by the discoloration of the conductor below. As this seems to be the panel nuetral, you might have some other problems all around soon...
[img]http://us.a2.yahoofs.com/users/43db47d7z80dafa65/6465re2/__sr_/82a1re2.jpg?phIKMJFBr1K3eBhH[/img]

Although I think the smoke you saw was from the coils, was really just drifting from the contacts, the fact that you got voltage at them while it was diconnected sounds odd. Is it at all possible that there is not a fault in the coils to ground? What where you measuring this 120 to? Ground of the can, or the nuetral? Do you have excessive voltage ground to nuetral? (While the loads are on.)

Either way it sounds as though you have a brain teaser - let us know what it eventually gets found out to be.

[This message has been edited by e57 (edited 10-05-2006).]

Great advice and ideas from everybody, but I am still banging my head into the wall. Here is a time line of replacement parts in this panel:
6/03-- 1st new contactor. Lasted 1 week
6/03--new coil kit. GE warranty. lasted 5 minutes
6/03--new coil kit. GE warranty.
8/03--new contactor. GE Warranty
2/04--new contactor. GE Warranty
6/04--new comtactor. GE warranty
1/05--new contactor. GE warranty
9/05--new coils. GE warranty
12/05--new contactor. GE warrant
8/06-- new coils GE warranty

I have had GE involved in this since June of 2003. They have sent field techs and checked out the building electrical system and found no problems. I can't really see the sending me this many new parts under warranty if they didn't have a known problem with this contactor.

e57, I would love to install a new lighting panel and it has been suggested to the customer more than once. I can't get them to do it yet. Anyway, thanks for the advice guys. I will let you all know what the "new field tech" from GE comes up with today.
Richard

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.