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2 registered
(Hutch, M_K)
and 22 anonymous users online.
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#170527 - 11/05/07 08:09 AM
correct way to wire a thermal overload switch
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MMK
Member
Registered: 11/02/07
Posts: 20
Loc: Ireland
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What is the correct way to wire the inbuilt thermal overload switch in an AC motor? I want to protect the motor in event of stall, but it should be safe, i.e. not start up automatically when motor cools down - in case some operator might get injured.
Michael.
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#170537 - 11/05/07 12:44 PM
Re: correct way to wire a thermal overload switch
[Re: MMK]
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mikesh
Member
Registered: 06/07/06
Posts: 196
Loc: Victoria, BC, Canada
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I think if you use a magnetic starter you need to wire for low voltage protection like a standard 2 button stop start. Place the overload in series with the stop button.
The start button is N.O. with holding contacts. Most other connections I can think of would let the motor restart on cooldown if there is no manual reset for the over load.
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#170540 - 11/05/07 01:21 PM
Re: correct way to wire a thermal overload switch
[Re: mikesh]
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MMK
Member
Registered: 11/02/07
Posts: 20
Loc: Ireland
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Mikesh,
Our current solution is to use a manual resettable current trip - external device.
Now though we are trying to use a dual voltage motor (see my other post) so that we can standardise machines for US(110) and European (230vac) markets. Problem is the current will differ by a factor of 2 and so the current trips would have to be different for both. Hence looking at using the inbuilt thermal switch in motor.
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#170550 - 11/05/07 06:21 PM
Re: correct way to wire a thermal overload switch
[Re: MMK]
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classicsat
Member
Registered: 11/23/02
Posts: 449
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The ones on the motors we use have two circuits, one through the heater, one not (or it could be dual heater/contact). When the motor is wired in 120V mode, the start and one run winding runs through the heater, the other run winding through the non heater contact. In 240V mode, the "other" run winding is in series after the first run/start winding.
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#170551 - 11/05/07 06:39 PM
Re: correct way to wire a thermal overload switch
[Re: classicsat]
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MMK
Member
Registered: 11/02/07
Posts: 20
Loc: Ireland
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Classicsat,
Could you please explain your suggestion a little more. What type (manufacturer) of motor are you using?
Michael.
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#170624 - 11/07/07 11:27 AM
Re: correct way to wire a thermal overload switch
[Re: MMK]
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pauluk
Moderator
Registered: 08/11/01
Posts: 7667
Loc: Norfolk, England
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One way or another, I think you're going to have to extend the thermal cutout contacts to the no-volt release holding circuit. Are you going to try to use contactor coils which are split wound to allow for parallel and series connection for the different voltages as well?
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#170630 - 11/07/07 02:23 PM
Re: correct way to wire a thermal overload switch
[Re: pauluk]
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MMK
Member
Registered: 11/02/07
Posts: 20
Loc: Ireland
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It is a single phase AC motor, 100W approx, so we are only planning to use a simple relay for on/off.
Can you get split wound contactor coils? This might be the solution for another application where we would like to use the same contactor for larger (5-11kW) pump motors, and which will operate on American 3ph (460V) and European 3 ph 380V.
Having to fit differing coils and/or different contactors becomes a logistical nightmare.
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#170634 - 11/07/07 04:35 PM
Re: correct way to wire a thermal overload switch
[Re: MMK]
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Alan Belson
Member
Registered: 03/23/05
Posts: 1367
Loc: Mayenne N. France
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Can I just say with my ex-production engineer and machine designer hat on: Build for the market. Customers can source spares easier, and you will find in the end that off the shelf parts will be less cost overall than complex circuits and 'special' components added to try and make 'one machine fits all'.
KISS = KEEP IT SIMPLE SIR!
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#170694 - 11/08/07 09:28 PM
Re: correct way to wire a thermal overload switch
[Re: Alan Belson]
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classicsat
Member
Registered: 11/23/02
Posts: 449
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They are Doerr (and other manufacturers) 1Ø Split Phase 60hz 1/2 to 2HP dual voltage capacitor start motors. We use them all over the place here, and I just rebuilt one a couple month's ago.
FWIW, I have, in a box someplace, some 3 pole contactors that are dual-winding; they can be set up for 120v or 240v use.
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