Using motor contactor as a lighting contactor - Electrician Talk - Professional Electrical Contractors Forum

coolbreeze419 · 08-08-2010, 02:12 AM

I recently came across a situation where banks of lights in a retail store weren't working. Upon inspection I found the wire on the line side of the contactor had burned completely through. The contactors that had been used were motor contactors instead of lighting contactors. Im assuming that the problem is that these contactors aren't rated for lighting loads but I can't seem to find any info on what happens when motor contactors are used as lighting contactors. Can anyone give me any info on whether or not this is the case and if so why is this happening.
Thanks

jrannis · 08-08-2010, 06:31 AM

Usually its a problem to use a lighting contactor on a motor. You should be good!

Some manufacturers make a generic contactor with an overload section as an option.
I would suspect that either the original termination was improper or possibly the contactor section of the starter is undersized.
If the terminal cannot be saved, maybe you can get an auxiliary contact rated for your load and save the day.

mcclary's electrical · 08-08-2010, 07:03 AM

Quote:

Originally Posted by coolbreeze419

I recently came across a situation where banks of lights in a retail store weren't working. Upon inspection I found the wire on the line side of the contactor had burned completely through. The contactors that had been used were motor contactors instead of lighting contactors. Im assuming that the problem is that these contactors aren't rated for lighting loads but I can't seem to find any info on what happens when motor contactors are used as lighting contactors. Can anyone give me any info on whether or not this is the case and if so why is this happening.
Thanks

What size starter, and what was the load?

micromind · 08-08-2010, 12:33 PM

I don't know about any other manufacturer, but the Allen Bradley NEMA motor starters and their NEMA lighting contactors use the exact same contactor. The starter simply adds an overload relay, and it's rated in HP, while the lighting contactor is rated in amps.

I suspect every other manufacturer is the same way.

coolbreeze419 · 08-08-2010, 03:06 PM

Well when I checked this out it was the third seperate occasion that this had happened. On 3 different circuits. I don't have too much experience with contactors aside from how to wire them. I wasn't sure if this was happening because the loads are unbalanced. Because I took an amp reading and it would be like 13 on A, 8 on B and 8 or 7 on C. I was thinking since a motor load would be the same across all the legs maybe that was the problem. Again, I just guessing with this.
Anyway the contactors being used are Square D definite purpose contactors. Rated for 25 FLA.
If this isn't being caused by the contactors, any idea why this is happening? My main concern at this point is that the wires are burning completely through and not tripping the breaker so there is a live wire in the enclosure. Definitely not an ideal situation!
Thanks for the input.

nitro71 · 08-08-2010, 03:11 PM

If the contactors aren't failing but the wires are melting I'd say your problem isn't the contactors. I would look at what amperage the conductors are fused at. What type of conductors they are.

coolbreeze419 · 08-08-2010, 03:24 PM

The wires are 12 guage stranded THHN on 20 amp breakers. The highest load I measured was 13 amps

mcclary's electrical · 08-08-2010, 03:47 PM

Quote:

Originally Posted by coolbreeze419

The wires are 12 guage stranded THHN on 20 amp breakers. The highest load I measured was 13 amps

Wrong crimper on a ring terminal??

coolbreeze419 · 08-08-2010, 04:27 PM

The whole install actually looked pretty legit. Really clean, wires zip tied, crimps on all the terminals. It wasn't janky at all. That's part of the reason I'm stumped. It doesn't look like a hack job. Looks like the guy knew what he was doing.
Although one other detail, either him or another EC told the owner not to flip all the switches at once because it could burn out the contactors. There are 15 contactors controlling 27 circuits. I think they're on 12 switches. Im not sure why someone would even design a system and have it set up where you couldn't flip all the switches at once, because you know that's exactly what's going to happen everytime. Of course, there are a lot of things people do that don't make sense!

oldtimer · 08-08-2010, 04:33 PM

Quote:

Originally Posted by mcclary's electrical

Wrong crimper on a ring terminal??

Good call: Where is the wire burning, in the contactor enclosure? Or at the the first joint? Do you have any pics?

I can't see the problem being in the contactor. If you have checked the contacts and they are pretty clean. One other thing. Does the contactor chatter?

Please let us know what you find.

coolbreeze419 · 08-08-2010, 05:10 PM

The wires are burning right at the contactor terminals on the line side. I have a pic but its from my phone and not close enough to actually see anything. I think the crimps were ok, but I didn't really check them out that close, they looked ok so I just didn't really consider that. Another thing, this started a couple of years after the original install and each incident was about 6 months apart, 3 separate occasions.
I might go take some pics tomorrow. I appreciate all the input.

coolbreeze419 · 08-08-2010, 05:16 PM

Oh, and they are the female disconnect crimps that go on a flag terminal. And they are the yellow ones which are for 10-12 guage, right? But if they were the wrong rating, would it take that long to burn out?

oldtimer · 08-08-2010, 05:53 PM

Quote:

Originally Posted by coolbreeze419

The wires are burning right at the contactor terminals on the line side. I have a pic but its from my phone and not close enough to actually see anything. I think the crimps were ok, but I didn't really check them out that close, they looked ok so I just didn't really consider that. Another thing, this started a couple of years after the original install and each incident was about 6 months apart, 3 separate occasions.
I might go take some pics tomorrow. I appreciate all the input.

Maybe a surge, lightning, or? I would remake the connections, and see what happens.

**MDShunk** · 08-08-2010, 06:01 PM

Quote:

Originally Posted by coolbreeze419

Oh, and they are the female disconnect crimps that go on a flag terminal. And they are the yellow ones which are for 10-12 guage, right? But if they were the wrong rating, would it take that long to burn out?

Yeah, "faston" terminals are not rated for that much current on a continuous basis. I have a chart somewhere in a book I'm going to try to look up.

**MDShunk** · 08-08-2010, 06:10 PM

Page 9 of this PDF lists the current capacity of faston type terminals. Yours seems to have been used within spec, so I'd start to think about an improperly applied terminal, or a terminal applied with the wrong tooling.

http://www.tycoelectronics.com/indus...004_FASTON.pdf

nrp3 · 08-08-2010, 06:12 PM

Which makes me wonder about a couple of heat pumps that have pressure terminals that don't look like they will accept the #8 stranded that I ran to them. I chose:

http://www.idealindustries.com/prodD...rminals_crimps

I bought the C-24 crimper to go with them. I haven't been able to find any rating for amperage. The bigger of the two calls for a wire to carry 34.8 amps with a max breaker of 50a. Both have the same contactor.

brother · 08-08-2010, 06:27 PM

As someone said I would remake the connections at the terminals and see what happens.

I will say this, that if the lights are on more than 3 hrs, then it is a continous load,must be rated at 125% branch circuit. I'm not sure about the contactors either, I guess we can assume they would be rated for continous duty at that amperage if they can be used with motors (assuming the motors running continous).