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How to size a contactor for a resistive load??

How to size a contactor for a resistive load??

How to size a contactor for a resistive load??

(OP)
Hello all -

I've got a 40 kW resistive load (heating elements) powered by 480V, 3ph. So FLA = 40kW / (480*sqrt(3)) = 48amps.

I require a contactor for this heating load (ie size 1, 2, 3 etc).

Can someone provide a table or chart that shows contactor sizing based on the resistive load?? I can't seem to find one online or in the NEC. I have the 2011 version of the NEC.

Thanks!! - Phillip

http://politicalplangetis.blogspot.com/

RE: How to size a contactor for a resistive load??

Use the thermal current or AC1 rating.

RE: How to size a contactor for a resistive load??

The NEC is not a design guide, they don't size components for you other than to say the minimum circuit ratings. Resistive switching is the easiest on a contactor. You mention size 1, 2, 3 ect., so I gather you intend to use NEMA rated contactors. With NEMA ratings, resistive ratings are the continuous ratings, actually slightly higher than the motor current ratings.  NEMA size 2 is rated 45A continuous, you would need to go to a size 3 for this application then. It will be rated for 90A.  

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RE: How to size a contactor for a resistive load??

(OP)
@ jraef

Is there a chart you can link me to online that shows NEMA rated contactors and their associated continuous amp rating?

Thanks

http://politicalplangetis.blogspot.com/

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