How to size a contactor for a resistive load??

[plangetee]

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/

 

[LionelHutz]

Use the thermal current or AC1 rating.

 

[Masbibe]

plangete,

You can read ABB electrical installation handbook, part 2, protection of feeders:

http://www02.abb.com/global/dkabb/d...elektriske+installationer+1SDC010002D0206.pdf

Milovan Milosevic

 

[jraef]

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.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
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[plangetee]

@ 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/

 

[JG2828]

Plangetee,

http://www3.sea.siemens.com/step/pdfs/cc_3.pdf