Motor Disconnect sizing

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sparkky302

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I am drawing a blank here and need some help. What I have is the following.
3 phase 480V Motor
HP-1.5
R.P.M-1750
Amps- 2.4
The existing starter is rated at 7 amps. The motor is just for an exhaust fan and does not use any Hand off Auto functions. They want to replace the starter with a fused disconnect. What size disconnect and fuses should I use?
 
Are the fuses going to provide your overload protection or does the motor have integral overload protection?

Chris
 
If the fuses are providing overload protection then they must be size at no more than 115% of the motor nameplate rating unless the motor has a marked service factor of 1.15 or greater or has a temperature rise of 40 degrees C or less, then the fuses can be size not larger than 125% of the motor nameplate full load current. (See 430.32(A)(1))

Are you sure that the motor does not have thermal protection built into the motor?

It will be difficult to provide overload protection with a standard fuses and a fused disconnect.

Chris
 
sparkky302 said:
I am drawing a blank here and need some help. What I have is the following.
3 phase 480V Motor
HP-1.5
R.P.M-1750
Amps- 2.4
The existing starter is rated at 7 amps. The motor is just for an exhaust fan and does not use any Hand off Auto functions. They want to replace the starter with a fused disconnect. What size disconnect and fuses should I use?
Click to expand...

see the below link may help you.


http://forums.mikeholt.com/showthread.php?t=122378&highlight=motor&page=3


http://forums.mikeholt.com/showthread.php?t=122274&highlight=motor
 
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