# Testing a contactor/thermal overload



## just the cowboy (Sep 4, 2013)

*Use a phase monitor*



ericksimo said:


> I manage the maintenance of a small aquaculture facility in the middle of the Pacific ocean. I have a fair degree of electrical knowledge and experience, but I'm new to three phase systems...
> 
> We had a 5hp motor on a water pump burn up on us. The utility company dropped a phase, the thermal overload did not trip even though the motor got very hot and melted the varnish on the windings.
> 
> I'm installing the new pump now. How do I test the contactor to be sure it will trip in the event of a future single phase situation?


Even though the starter may be working OK the motor can still burn up if it was running when it lost a phase.

Some starters have a test button on them to make sure it is not stuck.
Some you can remove a OL heater and it will trip (with voltage off).

Also check the nameplate on the motor with the OL setting.
The only sure way is with an electronic type OL or a phase monitoring relay.
Good luck.


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## backstay (Feb 3, 2011)

ericksimo said:


> I manage the maintenance of a small aquaculture facility in the middle of the Pacific ocean. I have a fair degree of electrical knowledge and experience, but I'm new to three phase systems...
> 
> We had a 5hp motor on a water pump burn up on us. The utility company dropped a phase, the thermal overload did not trip even though the motor got very hot and melted the varnish on the windings.
> 
> I'm installing the new pump now. How do I test the contactor to be sure it will trip in the event of a future single phase situation?


If phase loss is an issue there, a phase loss relay would help.


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## don_resqcapt19 (Jul 18, 2010)

Most electronic overload relays will trip on phase loss, but often the mechanical thermal ones won't.


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## ELECTRICK2 (Feb 21, 2015)

ericksimo said:


> I manage the maintenance of a small aquaculture facility in the middle of the Pacific ocean. I have a fair degree of electrical knowledge and experience, but I'm new to three phase systems...
> 
> We had a 5hp motor on a water pump burn up on us. The utility company dropped a phase, the thermal overload did not trip even though the motor got very hot and melted the varnish on the windings.
> 
> I'm installing the new pump now. How do I test the contactor to be sure it will trip in the event of a future single phase situation?


First you check nameplate of the motor and the rating of your over loads. A lot of times guys install what ever O/L they have on hand (usually too big). If these match up, the next step (if you're qualified to work on electricity) is you have to make sure the O/L contacts are actually wired into the circuit. Seen lots that weren't. O/L might trip but if it's not in the circuit motor keeps trying to run and burns up.


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## Bogart (Jul 20, 2015)

backstay said:


> If phase loss is an issue there, a phase loss relay would help.


A phase loss relay is exactly what you will need and I usually suggest them on any Motor over 5hp...it is a small price of preventative maintenance to pay for the down time and cost of replacing/rewiring a new motor.

http://www.galco.com/buy/Symcom/460...mWAC-QuNsK-2C4cOHaaD41orefgykvv-hkaAp4n8P8HAQ

However, Your O/L still should have tripped. But then again that is dependent on the O/L itself, the actual load on the motor and the O/L settings. My advice ....Install Phase loss relays on all 3Ø motors unless the O/L set up already has them incorporated...Most newer IEC O/L relays are incorporating them into the design


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## John Valdes (May 17, 2007)

ericksimo said:


> I manage the maintenance of a small aquaculture facility in the middle of the Pacific ocean. I have a fair degree of electrical knowledge and experience, but I'm new to three phase systems...
> 
> We had a 5hp motor on a water pump burn up on us. The utility company dropped a phase, the thermal overload did not trip even though the motor got very hot and melted the varnish on the windings.
> 
> I'm installing the new pump now. How do I test the contactor to be sure it will trip in the event of a future single phase situation?


Unless you get lucky and the phase that gets dropped is the phase the control power is derived from. Addressing the contactor will do nothing for phase loss.
I'm with the other guys. Get a phase loss prevention device/relay and have it open the control circuit thus dropping out the contactor.


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## ericksimo (Dec 14, 2015)

Looks like I will be adding a phase loss prevention relay. Thanks for all the information!


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