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Author Topic: Overload wiring for 1 phase Motors  (Read 5406 times)
DaveW
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« on: July 26, 2006, 01:19:24 AM »

I have a 1 phase 240VAC motor that I need to wire using a 3 leg contactor and overload.  With the contactor, I will use just 2 of the 3 legs but I'm not sure about the overload.  Should I just wire through 2 legs of the overload?  I was thinking of wiring one leg through one overload leg, and the other leg will be looped through the 2nd and 3rd leg of the overload.  Any thoughts?
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burnerman
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« Reply #1 on: July 26, 2006, 05:49:37 AM »

Most 3-phase overloads have single-phasing protection to protect a 3-phase motor from the effects of losing one of the phases - if the current flowing in all 3 legs is not the same it will trip.

Normally I would take the neutral direct to the motor, not through the contactor/overload. Then take the live feed through all three legs of the contactor/overload (down-up-down).
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DaveW
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« Reply #2 on: July 26, 2006, 01:19:27 PM »

Quote from: "burnerman"
Then take the live feed through all three legs of the contactor/overload (down-up-down).


I was thinking of the same thing but would it matter which motor leg goes through 2 poles of the overload?  Or should I just leave one pole of the overload unconnected?  I'm using the Allen-Bradley 193-EA1FB overload
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David Emmerich
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« Reply #3 on: July 26, 2006, 06:15:31 PM »

Hi DaveW...Loop thru all three poles on the overload unit...like Burnerman said, some units will trip if they see an unballenced load.

David
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silva.foxx
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« Reply #4 on: July 27, 2006, 11:02:06 AM »

You can do two things..either:

a) Series connect the three poles of the contactor/overload. If one of the pole contacts fail then the continuity is broken.

b) Parallel the three poles of the contactor/overload. If one of the pole contacts fail the overload will false trip resulting in unnecessary fault finding.
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jraef
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« Reply #5 on: July 27, 2006, 02:39:04 PM »

No, you cannot "parallel" the overload connections, it will not accurately detect current.

That is a Solid State OL relay, and it DOES have phase loss protection, so you MUST run 2 of the phases in series, that is the only way it will work. That OL relay also is designed to stab directly into an A-B contactor, so if that is how you are using it, then you will need to series connect through the contactor as well. If it is stand-alone (i.e. you have a mounting base for it), it isn't necessary to go through the contactor too.

Either way, the conventional hookup is to come in to L1, out of T1 and loop back to L2, out of T2 to the motor. The other connection just goes in to L3 and out of T3. It really doesn't matter which phase you do it on, but sticking to conventions is helpful to someone else in the future who is troubleshooting so that he doesn't have to try and guess why you did it differently.
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jraef
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« Reply #6 on: July 27, 2006, 02:42:26 PM »

Here is a link to A-B's site on this relay, drawing at the bottom of the page.

193 OLR
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DaveW
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« Reply #7 on: July 28, 2006, 12:06:54 AM »

Jraef, thanks for clearing that up.
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silva.foxx
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« Reply #8 on: July 29, 2006, 08:34:33 PM »

Quote from: "jraef"
No, you cannot "parallel" the overload connections, it will not accurately detect current.


Quite right....I must have had a "senior moment" and dreaming of contactors.  :oops:
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