# Contactor ?



## mutabi (Jun 2, 2009)

Possibly an MOV?
http://en.wikipedia.org/wiki/Varistor#Metal_oxide_varistor

Used to suppress spikes from the coil energizing/de-energizing.


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## bruce6670 (Apr 27, 2010)

Thanks. That looks like what was on there. :thumbsup:


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## Jlarson (Jun 28, 2009)

They might have been RC snubbers too.


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## RSmike (Jul 31, 2008)

If the coil is DC it could be a diode. AC? It could be an RC snubber.

If the coil is driven by a solid state output the device is there to pull leakage current to ground to prevent the relay from 'chatterning'. Solid state devices never really turn off all the way. Even when off they leak a little bit of current. Some relays are sensitive enough that they can pull in from this leakage current; probably won't bother a big contactor.

Most leakage current is usually under 10mA or so and more like 2mA if you are dealing with PLC outputs. The snubber device pulls this current to ground and away from the coil. It's good practice to put this in but they are not always needed. I don't know of a case where putting them in is a bad thing. I use them as needed depending upon the application. I tend to notice that the smaller ice cube relays are the only relays sensitive enough be pulled in or even 'buzz' from leakage current.

If you are dealing with DC the device could be a diode. When coils turn off the field collapses and this can create an inductive kick. If you are using relays to drive other relays it can help to prolong contact life if the inductive effect is reduced. In DC land putting a diode across the coil causes this field to short through the diode which minimizes the big blue flash across the contact. Putting a voltage sensistive snubber can prolong contact life.

I'd do not put snubbers on contactors. They usually have enough resistance to pull the leakage current to ground.

RSlater,

RSmike


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## bruce6670 (Apr 27, 2010)

Thanks for the detailed response. 

The contactors were AC and were for several different purposes. They controlled different operations on a draw bridge. To the best of my knowledge, most of them were control by the PLC.


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