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Old 08-03-2019, 07:46 AM   #1
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Default Wondering why these contactors keep burning up


Hopefully the above comes out to be a picture of contactor in question. The story behind it is that this is the third one that has melted in the same way. Line Two burned all the way through and line 1 showing minimal in comparison. This is installed on a grain bin and has automated control that is giving the signal to start and stop the fan. I am the second electrician called out to look at it about three months ago. I replaced a contactor that had failed about identical to the pic. I did a fairly thorough step by step with voltage readings. The only noticeable thing at that time was that there was not a true neutral that went through the overload. I was able to correct this and added a breaker in the panel. Upon replacing I once again checked voltage and amp draw. Everything tested fine, and a couple days later I had the farmer take a look at it for physical signs of overheating and all was good, but just received word that that this one burned up in like manner.
Someone suggested a brown out has been used in cases that there were repeated motor failures. I am not familiar with what exactly they do to give an opinion- it says overvoltage and under voltage protection. Wondering what some thoughts were.
Another thing mentioned is the mars relay in the motor, and once again I am lacking in experience to make a solid decision.
My thoughts are a recording meter would be nice. It is interesting to me that all heat is on line side and nothing on the load. It is a application where a second fan was added and there was mention that they are one of the last ones on utility line.


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Old 08-03-2019, 07:54 AM   #2
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Improper torque, undersized starter, motor going bad, improperly set o/l’s... Pick your poison and go from there.
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Old 08-03-2019, 08:03 AM   #3
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Torque question-I don’t have torque Allen wrench but tightened well thinking of vibration especially being on fan and first failure.
Undersized starter and o/l I wish I had better memory I believe them to be right but cannot say beyond a shadow of a doubt because I have made mistakes. The farmer bought the contactor and had it there. The overload was used was the same on both so possibility the overload may be the problem. I did not change setting.


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Old 08-03-2019, 09:02 AM   #4
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The problem is there is more than one device in the enclosure. Everyone knows that more than one contactor or relay in an enclosure is the source of most failures.
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Old 08-03-2019, 09:07 AM   #5
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Is that aluminum wire feeding the contactor? Are LC1 contactor terminals rated for aluminum? I never thought to check since I always wire them with copper.
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Old 08-03-2019, 09:10 AM   #6
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Looking back at pic. I am more aware of the need for a little tidying up and organizing of wires.
I am thinking the only other wiring that goes through there is the wiring a heater.


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Old 08-03-2019, 09:27 AM   #7
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You say it's supply side overheating. What condition are those conductors in after so many times of overheating?
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Old 08-03-2019, 09:32 AM   #8
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I thought this was a post about spontaneous human combustion.


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Old 08-03-2019, 09:41 AM   #9
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Originally Posted by Going_Commando View Post
Is that aluminum wire feeding the contactor? Are LC1 contactor terminals rated for aluminum? I never thought to check since I always wire them with copper.


Looked on line and could not verify specs for terminal, but talked to someone at Schneider dealer and he said possibility so will splice some copper to aluminum before landing again.
Also mentioned that could change out coil from 120volt to 110 if it is 120 that is currently on it, in case voltage does drop and cause chattering. Thanks.
Hoping to have good game plan because it is 2 1/2 hours from the house to the site.


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Old 08-03-2019, 09:46 AM   #10
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You say it's supply side overheating. What condition are those conductors in after so many times of overheating?


I cut back what I can see, but the integrity of the cable itself probably is somewhat compromised. The only thing with that is direct burial with no raceway so that would make it a lot bigger job then the onset if I supply a new feeder. Hoping that it is salvageable.
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Old 08-03-2019, 10:27 AM   #11
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Seeing that red jumper, tells me this is a single phase application?

This is what I would do:

Verify motor HP, FLA, phase.

Verify aluminum wire size is correct.

Verify starter is rated for single phase HP rating. I'm not a fan of IEC, I would lean towards a NEMA starter replacement myself, I'd even buy a used and tested NEMA starter from one of our surplus dealers if cost was an issue.

Pigtail to copper at the starter.

Verify all connections are good from the service through the starter and to the motor.

I'd start the motor and verify voltage is good at the line terminals at the starter.

If the motor is a good distance away, I'd also measure voltage when starting at those terminals for good measure.

It also never hurts to verify control wiring is good and tight at it's terminals.

Also, verify control power is good while starting the motor as well to make sure the starter is not dropping out or chattering during inrush.

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Old 08-03-2019, 11:14 AM   #12
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Everything Cow said +

When you tail some copper on softer (more strands) is better for control wiring. Aluminum sucks, I feel like that's the issue.

Check all the way down the line.. Just because the supply side burns off it doesn't necessarily mean that's where the problem is... could be a loose splice in the device

Double check the contactor assembly to the overloads sometimes it gets loose.

The further down it is on the utility line the greater the possibility of fluctuating low voltage or high voltage dependent on draw and time of day. IE if utility company had to boost voltage with a xfmr for daytime because of low voltage, at night it's possible that a 115V low can turn to 128V high as others aren't consuming as much power.

There's a cheap logger you can get by MTP about $150, sold as a secondary metering device.
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Old 08-03-2019, 11:21 AM   #13
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Always check the motor for size, never trust the guy before you in setting the o/l’s correctly.

+ What Cow & Fishinelectrician said.
A fused NEMA Starter all the way. I hate IEC sizing, no room to fart or wiggle out of the way.


* Is that held in place with Zip Ties?
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Old 08-03-2019, 11:37 AM   #14
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Thanks guys, I really appreciate this forum. It helps get an overall perspective. I sometimes think I should be contributing more on certain feeds, certain ones at certain times I have felt like I can offer back. I have increased my learning every time I have scanned through posts and comments. Thanks again. Hope everyone is having a good weekend.


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Old 08-03-2019, 12:11 PM   #15
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Quote:
Originally Posted by Family guy View Post
Torque question-I don’t have torque Allen wrench but tightened well thinking of vibration especially being on fan and first failure.
Undersized starter and o/l I wish I had better memory I believe them to be right but cannot say beyond a shadow of a doubt because I have made mistakes. The farmer bought the contactor and had it there. The overload was used was the same on both so possibility the overload may be the problem. I did not change setting.


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I dont see smashing of copper. Are you sure its tight terminals? Did you do the wiggle wiggle retight?

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Old 08-03-2019, 12:42 PM   #16
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I would not land AL directly on the contactor terminals. It looks like there's room for pin connectors but you'd need a crimper. Another way would be to use setscrew butt splices and a short piece of CU. Use some sort of anti-oxidation AL joint compound (like NoAlOx or Penetrox) on the AL termination.

That contactor is rated for 15 HP single phase. If the motor is 12 - 15 HP, I would consider going to a larger contractor. A NEMA 15 HP contactor will handle a 15 HP motor, and IEC one is questionable.
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Old 08-03-2019, 12:49 PM   #17
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I dont see smashing of copper. Are you sure its tight terminals? Did you do the wiggle wiggle retight?

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I see what you are saying. Got me thinking now. I tightened them then used Klein’s to give extra torque, but would be nice to see more indentation on the conductors for conscience sake at this point.


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Old 08-03-2019, 01:03 PM   #18
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Just out of curiosity, did you pull the cover and check the contacts themselves? Or at least do a V/D (FOP) test across them?
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Old 08-03-2019, 01:18 PM   #19
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Big motor loads pretty much demand copper conductors.

So much so that this is spec'd in the typical contract.

Aluminum -- even the more modern alloys -- just expand and contract too much.

And... they're SOFT.

So they deform under expansion and then pull away and back off during no load// cooling off.
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Old 08-03-2019, 01:21 PM   #20
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Just out of curiosity, did you pull the cover and check the contacts themselves? Or at least do a V/D (FOP) test across them?


I checked line side voltage when energized and again after fan was running. I replaced it with a new contactor so I did not check contacts, probably should have on the one that had previously failed.


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