Hi Guys,
How would I calculate the rating of the overcurrent device for a 5.5KW
3ph 415v motor?
Cheers,
Bob
motor protection question
Sep 20, 2006
2 Replies
3ph 415v motor?
You usually use the nameplate "FLA" (full load amps) rating but if that 5.5kw is actually an accurate measurement you could go with that. I fear it is really more of a marketing number like the "HP" rating of US motors. If I use 5.5kw divided by 415v and then divived by 1.73 to account for
3p I get 7.66a for a FLA number. Conductors would be sized at 125% of that (9.75) so a conductor suitable for 10a would suffice (in the US that rounds up to 14ga) If the motor has another means of overload protection in the starter or internally the branch circuit overcurrent device can be up to 250% of the FLA so it could be 25a. Proper design would use the smallest O/C device that would reliably start the moptor.
OK. Thanks for that
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