# Contactor Chattering



## Voltech (Nov 30, 2009)

I have a LCP (lighting control panel) that when I turn on the line voltage to supply the LCP the contactors chatter when when they close. I dont have any of the circuits that are controlled by the contactor on and they still chatter. I did notice my supply voltage was about 118.5 on B phase and around 120.0 on A phase. but it chatters the same on either phase. I have been told that 1.5 volts below 120 could cause problems like this. 

Once or twice they didnt chatter. I have made sure everything it tight and there is no trash in the box. Its six 4 pole contactors.

Any advice?


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## wildleg (Apr 12, 2009)

get mechanically held contactors or invert the inputs so the lights are on when the contactors are off (then they'll chatter when no one is there) (if that's an option)


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## stuiec (Sep 25, 2010)

missing shading coils?


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## erics37 (May 7, 2009)

I doubt you would have problems with 118.5 volts. Did you measure the voltage when the contactor coils are actually energized?


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## OaklandElec (Jan 4, 2011)

wildleg said:


> get mechanically held contactors or invert the inputs so the lights are on when the contactors are off (then they'll chatter when no one is there) (if that's an option)


Yup.


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## 480sparky (Sep 20, 2007)

It still may be a voltage issue. Your meter may say 118.5v, but the sampling rate may not be fast enough to catch a voltage drop issue. The voltage may drop down enough for the coil to release, then the voltage will come back up. This happens quite quickly, and a low-end meter won't see it.


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## A Little Short (Nov 11, 2010)

Can you change the coil, or is it built in with the contactor so that it can't be changed? If you can, I would try another coil.


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## bobelectric (Feb 24, 2007)

Bad photocell? (hopefully not a timer).


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## zgozvrm (Jun 17, 2009)

In my experience, a couple of things can cause a situation like this:

- The wrong type of core (the part that gets magnetized). The construction of the laminations in a DC mag core is different from that of an AC mag. Although the coil itself may be correctly rated, the core could be the wrong type.

- Mechanical misalignment. This is the most common cause of contactor chatter. If the faces of the stationary and moveable cores do not come into complete contact, chatter will result. Dirt/corrosion can cause this, as can mechanical binding.


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## Jeff85 (Oct 22, 2011)

I doubt it is voltage. Most coils still work plus or minus ten percent on the voltage. It could just be a bad coil. I have had brand new ones go after working for a few days. All it takes is some dirt to get in there and they don't close fully.


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## jmsmith (Sep 10, 2011)

A lot of the older contactors that I've seen this with had to do with the pole-shading coils that were inserted into the laminated cores itself. These would either break or wear to the point that they would simply fall out. I worked at several plants that kept these in stock for all the contactor sizes that they used. A lot cheaper than replacing the entire core!


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## Voltech (Nov 30, 2009)

Well I fixed it somehow, kinda. I took the contactors out and apart to make sure there was not anything in there that didnt need to be. A guy at work told me to put a small amount of lubricant where the spring is. I didnt find any trash. It wont chatter all the time but will at times. I only know this by turning it on and off a few times during the day.


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## Voltech (Nov 30, 2009)

480sparky said:


> It still may be a voltage issue. Your meter may say 118.5v, but the sampling rate may not be fast enough to catch a voltage drop issue. The voltage may drop down enough for the coil to release, then the voltage will come back up. This happens quite quickly, and a low-end meter won't see it.


My meter would not catch that. Would this happen even if there was no load applied? It would still chatter with all the controlled circuits turned off


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## brian john (Mar 11, 2007)

Voltech said:


> My meter would not catch that. Would this happen even if there was no load applied? It would still chatter with all the controlled circuits turned off


This issue would be independent of load. The coil load, with the coil inrush could be sufficient for this.


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## dmxtothemax (Jun 15, 2010)

Voltech said:


> I have a LCP (lighting control panel) that when I turn on the line voltage to supply the LCP the contactors chatter when when they close. I dont have any of the circuits that are controlled by the contactor on and they still chatter. I did notice my supply voltage was about 118.5 on B phase and around 120.0 on A phase. but it chatters the same on either phase. I have been told that 1.5 volts below 120 could cause problems like this.
> 
> Once or twice they didnt chatter. I have made sure everything it tight and there is no trash in the box. Its six 4 pole contactors.
> 
> Any advice?


 Do they keep chattering ?
Or do they only do it for a short period ?
Can you not change the contactor ?
I dont really think a small reduction in line voltage
would cause issues like this.
More likely the contactor is faulty or wrong type.


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## captkirk (Nov 21, 2007)

zgozvrm said:


> In my experience, a couple of things can cause a situation like this:
> 
> - The wrong type of core (the part that gets magnetized). The construction of the laminations in a DC mag core is different from that of an AC mag. Although the coil itself may be correctly rated, the core could be the wrong type.
> 
> - Mechanical misalignment. This is the most common cause of contactor chatter. If the faces of the stationary and moveable cores do not come into complete contact, chatter will result. Dirt/corrosion can cause this, as can mechanical binding.


 wouldnt an ac coil on a dc circuit just burn out..?


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## zgozvrm (Jun 17, 2009)

captkirk said:


> wouldnt an ac coil on a dc circuit just burn out..?


I'm not 100% sure, as I haven't come across that yet (nor have I tried it). Although I _have_ seen it the other way around. The life of the coil _may_ be shortened in either case, but I don't think it would burn out immediately. After all, the voltage potential is there.


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## jza (Oct 31, 2009)

I had a contactor do this once. Had to replace it with a contactor intended for lighting loads.


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## JRaef (Mar 23, 2009)

99% of the time a contactor chattering is the result of either debris on the armature pole faces, or a broken shading coil. Most modern coil systems are designed to have a "knee point" threshold in the applied voltage, so above that, it works, below that, it doesn't. It is REALLY difficult to have a voltage that hovers EXACTLY at that knee point. And per NEMA design criteria, coils are supposed to have 85% drop out voltage tolerance. So a 120V coil should hold in down to 102V WITHOUT chattering. That's not to say you can't find cheap Chinese knock-off products that don't bother to use industry standards, but since you didn't post the make and model of your contactor, I have no way of knowing.

A less common issue, but mostly happening in some types of multi-pole lighting contactors, is a side-to-side mechanical imbalance on the number of poles. Most contactors are designed as 3 pole devices (or 4 pole for small IEC style), then on some *lighting* contactors you can add pole expansion units to each side. But they must be balanced in terms of the weight if you do that. So if you add on poles, you must add them on in pairs so that if your contactor was originally designed as a 3 pole device, you always end up with an odd number, i.e. 5, 7, 9 etc. The ones that do this then will have a "dummy pole" that you add if you don't want to pay for a full power pole. So if yours is that type, then for 6 poles you would have 2 add-on power poles on one side, one on the other side, and a dummy pole on that side so that it balances the mechanical forces on the armature. Without it, the armature pulls in crooked and chatters. If you have a multi-pole lighting contactor that was shipped from the factory as a 6 pole unit, that shouldn't be an issue though.


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