# Contactor trouble



## oldtimer (Jun 10, 2010)

spook said:


> I just have a quick question about a contactor. Its a furnas 3 phase 120v coil and it just stops working for a while then pulls the coil back in on its own. When it releases it still has 120 on the coil but just lets go and then come back on by itself about 10 15min later. Its almost like it has a thermal overload in it. I'll admit I dont do much service work but Ive never seen one do this. Ive had them buzz and chatter and burn up but never just stop working on its own. Its rated for 120amps and draws about 50 across each phase so its not like its over loaded. I was just curious if this is common or not.


 Do all three phases open?

From what I gather, the coil is rated at 120 volts, but what is the 

voltage across the contacts?

Also, is the coil voltage supplied from another source?


----------



## mbednarik (Oct 10, 2011)

i would swap out the coil. I have never seen this in a contactor, but i had an ignition coil on my old pickup that must have had a break in the wire and when it warmed up it would open up. If you have 120v at the coil and it opens, sounds like you are loosing a circuit inside the coil.


----------



## oldtimer (Jun 10, 2010)

mbednarik said:


> i would swap out the coil. I have never seen this in a contactor, but i had an ignition coil on my old pickup that must have had a break in the wire and when it warmed up it would open up. If you have 120v at the coil and it opens, sounds like you are loosing a circuit inside the coil.


 Loosing a circuit inside the coil????

W T F does that mean?


----------



## spook (Oct 20, 2011)

oldtimer said:


> Do all three phases open?
> 
> From what I gather, the coil is rated at 120 volts, but what is the
> 
> ...


yes the coil is supplied from a different panel and supplies an identical contactor right beside it. All three phases open and its 208 across the contacts and 120 across the coil.


----------



## mbednarik (Oct 10, 2011)

oldtimer said:


> Loosing a circuit inside the coil????
> 
> W T F does that mean?


it means the winding opens, loosing the circuit. no circuit, no magnetism, no pull.


----------



## mrmike (Dec 10, 2010)

The voltage on the contacts should have nothing to do with this coil making and breaking. I'm sure the coil will not be fed from the contacts.

You either have a weak coil or you are losing the full voltage to it intermittingly. Check connections, etc from the coils source of voltage. If they are ok I would change out that coil.

I used to take care many MCC's and in one of them the A/C used to quit quite often. The same starters would drop out all the time. I found that the coils were weak in these & the heat would be enough to drop them out................


----------



## spook (Oct 20, 2011)

mrmike said:


> The voltage on the contacts should have nothing to do with this coil making and breaking. I'm sure the coil will not be fed from the contacts.
> 
> You either have a weak coil or you are losing the full voltage to it intermittingly. Check connections, etc from the coils source of voltage. If they are ok I would change out that coil.
> 
> I used to take care many MCC's and in one of them the A/C used to quit quite often. The same starters would drop out all the time. I found that the coils were weak in these & the heat would be enough to drop them out................


Ok thanks for all the help. I talked to the owner and I guess they are having some issues with the contactors period and alot of other little stuff in the building. So he asked if I could get him a price to just replace both contactors. He also asked about replacing all his track lighting with led's and he has 8 stores with 5000 bulbs so that would keep me busy for a little while. Thanks again for all the info and help.


----------



## GEORGE D (Apr 2, 2009)

Probably unlikely but be sure the return path is not the problem.


----------



## noarcflash (Sep 14, 2011)

I tried to find a furnas overload relay. discontinued, no where to be found. I ended up removing it from the motor starter, and bypassing it. 

we will replace the entire magnetic motor starter next trip out.


----------



## oldtimer (Jun 10, 2010)

noarcflash said:


> I tried to find a furnas overload relay. discontinued, no where to be found. I ended up removing it from the motor stater, and bypassing it.
> 
> we will replace the entire motor stater next trip out.




Sorry! I misread, motor stater? Motor Starter!

I always called that a contactor!

Different terms, I guess.

It is to your advantage to replace the contactor/starter.

Especially if the Furnas brand is no longer available.


----------



## noarcflash (Sep 14, 2011)

actually I meant Magnetic Starter.
the whole box with the push buttons and relays, and the heater OL strips.


----------



## MDShunk (Jan 7, 2007)

If you're measuring 120v at the coil, and it has the starter dropped out, there's really only once choice. The coil is bad. I've also seen the core laminations so rusty that the coil will buzz hard, but never seen it cause one to drop out.


----------

