# Auxilliary Contact Testing



## Big John (May 23, 2010)

I don't know of any reliable way to do this with the contactor still in the cell. The closest you'd get would be to pick up the control points where they leave the cubicle and put an ohm meter on them, but that wouldn't be precise enough to detect anything except an active failure.

The best bet is to pull it out and do a visual inspection and cleaning on open-frame contacts, or a ductor on enclosed contacts.

But I'd also add that if these are seeing so many operations that your auxes are getting that abused, I would be concerned about the integrity of everything else in that contactor and it sounds like it needs overall PM.


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## Peewee0413 (Oct 18, 2012)

Resistance? visual inspecting? That's just about all you can do..


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## Tsmil (Jul 17, 2011)

Some time ago, I ran into a similar problem where the aux contacts activating the brake would fail frequently. We solved this by adding a second contactor( a small one) to control the brake and ran the control wire for the motor contactor through the brake contactor. This way the brake would have time to disengage before the motor would start.


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## mbednarik (Oct 10, 2011)

A VFD or solid state relay may be in your future.


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## xlink (Mar 12, 2012)

If the load is large enough you might try a sensitive voltmeter that can read millivolts (fluke 87 eg) and take a voltage reading across the contacts when they are under load. If you take enough readings you'll get a feel for what is normal.


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## DesignerMan (Jun 13, 2008)

The way I've done it is to read the voltage across the contact while it's running. This should read zero, so anything above 0.1 I visually check when the equipment is offline next. This has worked for me for many years...


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## Wirenuting (Sep 12, 2010)

Like Big John said, a good PM program is a must. 
Keep better records and you will see which aux contacts give you troubles. You will learn to replace them before they fail. It's the easier and least costly way to go. 
Preventive maintenance or predictive repairs.


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## Southeast Power (Jan 18, 2009)

Is the brake directly controlled by the aux contractor?
Are you having the problem with just one or all of your brake motors?
Would I be correct in assuming that you have a rectifier in that brake circuit?
What voltage is operating your brake circuit?


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## gnuuser (Jan 13, 2013)

DesignerMan said:


> The way I've done it is to read the voltage across the contact while it's running. This should read zero, so anything above 0.1 I visually check when the equipment is offline next. This has worked for me for many years...


designerman is correct auxiliary contacts should read zeroacross the contacts while running
pitted contacts in a braking circuit can cause severe problems with the motor.
xlink is correct also 
a very sensitive voltmeter such as a vtvm (vacuum tube volt meter)
(these ultra sensitive meters were widely used in the television/ radio industry as well as the military for diagnosing problems in syncro/servo systems) could measure resistances that other meters could not.

http://www.heathkit-museum.com/test/hvmim-11.shtml


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## John Valdes (May 17, 2007)

rmb said:


> Hi, first post. I work at an industrial facility and was wondering what the best way to test auxilliary contacts and contacts in a contactor was. I am a level 4 apprentice and the journeymen here seem to basically guess at it, no real testing involved. I have seen you can use a scopemeter, any other suggestions? Would like to find a technique to detect arcing damage before it affects controls. We have an application where the contactor/motor starter closes and it also closes the auxilliary contact to release the brake, problem is that if the auxilliary is pitted/burnt it releases the brake with a delay and as the motor starts 4 times a minute (600V, 3phase) it can warm it up a bit too much and burn it out.


Have this contact energize a small contactor just for the brake coil. Or eliminate the contact altogether. The contact rating may be to low for the coil current and inrush current.

There is no accepted method of testing a single contact.
Unless you work in a laboratory and have the equipment to trend the life cycle of the contact, just forget about testing it and replace it as needed or include the option I explained first.


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## journeymanj (Dec 30, 2010)

Every thing stated above is correct. Usally Ohm reading is typical, another thing u could do if u want to get crazy is DLR test. This is a digital low resistance tester. Our high voltage guys use it on HV contactors. But this seems vary unpractical. Every thing stated in other posts is acceptable where I work.


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