4 pole contactor switching single phase


Old 04-20-10, 06:45 AM
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4 pole contactor switching single phase

I have a 4 pole 40A contactor that I want to use to switch a 50 amp single phase load. My intent is to use the 4 contactor relay terminals as 2 unique sets, each switching what would be a 25A single phase load.

A guy at an electrical supply house told me that this wouldn't work and I needed a 2 pole contactor. My response was that a contactor isn't that intelligent and it's only function is to open or close a set of contacts and the contactor itself doesn't know or care about the source load(assuming it's within the capacity of the contacts). Am I right or wrong.

Much the same as using only 2 poles of a 3 pole contactor to switch a single phase load.
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Old 04-20-10, 08:19 AM
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You can do it if the total load is such that it is actually broken up into two discrete 25A loads -- two motors or two heating elements for example. Each "side" of the contactor would be controlling one of these elements.

You cannot do it if you just parallel conductors for a single 50A load. That would require a contactor rated at 50A or the HP rating of the motor if this is a motor load.
Old 04-20-10, 08:24 AM
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A 40 amp contactor is not rated to carry a 50 amp load. (Be sure to read the fine print because some contactors have different ratings depending the type of load you are carrying) Current is not divided between each leg, each leg carries the full amount of current depending what part of the wave form you are at at a particular time.
Old 04-20-10, 08:26 AM
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IPBooks, It is to control 4 distinct heating elements(2 on each side). I should have been more specific on the intended load. Thanks for confirming. Ed
Old 04-20-10, 12:43 PM
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Are you planning to have two Branch Circuits , one for each of the two sets? The "Line" conductors from the panel , and "Load" conductors to the loads , should be the same guage wire.

Also , for this type of load , the ampacity of the conductors should be the load-current X 125%.

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