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Old October 18th, 2018, 08:20 AM   #1
kongshitt
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Confused by a motor contactor

So, ran across a part today that I can't really figure out where it would be used.

Its a 4 wire contactor with a NC circuit, when you power the coil it drops power from the load side. To me thats a safety type relay, but I don't see where you would want to use that on a motor. Also, it has 4 high load terminals no AUX like most AB relays.

Just looking for some knowledge because were all here scratching our heads saying why would we ever use this?
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Old October 18th, 2018, 08:34 AM   #2
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Maybe for a crane with electromagnet for picking up stuff ?
When the E-stop is pressed, or if there is some kind of electrical problem, the electromagnet defaults to ON. This so it does not drop a ton of steel onto some unfortunate person.
Of course the power supply for the electromagnet must still be on for this to work. I have seen this before as an example of an electrical circuit that should be exempted from the E-stop circuit.
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Old October 18th, 2018, 09:15 AM   #3
kongshitt
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Makes sense, but like you said, if its it's a power problemproblem, the magnet releases anyway. Thanks!
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Old October 18th, 2018, 09:43 AM   #4
scott.lawrence
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sounds like this was possibly been used in a two-speed motor set-up
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Old October 18th, 2018, 10:40 AM   #5
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May the 4th NC contact is for an electromagnetic brake?
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Old October 18th, 2018, 11:19 AM   #6
saultgeorge
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4th N.C. contact could possibly be for a circuit that would power a "motor off" light.
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Old October 18th, 2018, 12:00 PM   #7
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Probably an old “DC drive contactor”. The NC pole was used in a braking scheme when you absolutely wanted braking every time the drive turned off, like on a hoist. Not much call for them any more, most everyone has gone to AC drives on hoists now.
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Old October 18th, 2018, 12:18 PM   #8
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I interpreted the OP's description
Quote:
when you power the coil it drops power from the load side
as all four of the contacts are NC and all four are rated for full current.
kongshitt, please clarify.
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Old October 18th, 2018, 04:10 PM   #9
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i have seen some 4poles with 2 power no and 2 power nc terminal for forward/reverse action on a single coil.
4 NC could also be for load control system. A controler that remove heaters or other non mandatory load to limit the peak read by the utility meter. NC or mechanically held contactor are used to avoid the ''humm'' noise of holding a NO closed in some offices or quiet workplaces...
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Old October 20th, 2018, 09:38 AM   #10
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It is probably used or as a simple on/off contactor as the motor stops when two wires are open.
or can be used to change direction.
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Old October 20th, 2018, 09:55 AM   #11
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It could be as a safety relay to kill all power when activated, when the E-Stop relay shuts of it has a NC contact that would then power this contactor, which would interrupt all power.

Sort of like the N.O. solenoid valve I put on the water meter at my house - if my alarm PLC detects a flood in the basement, or I activate it by the HMI, powering the SOL on shuts off the water to the house. That way I don't have to keep the valve powered on constantly, only when I want to shut off the water.
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