Sizing wire for a soft start.

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125% of what?

Let's put it this way, sizing conductors for motors controlled by soft starters is no different than sizing them for any motor controller, except VFDs. So you can't size it for less than 125% of the motor FLA from the NEC chart. You can size it for more if you like though...

VFDs are the only type of AC (squirrel cage induction) motor controller that has special rules for conductor and OCPD sizing, and that is just 125% of the VFD Max Amp Rating, not the motor connected to it.
 
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Jraef said:
125% of what?

Let's put it this way, sizing conductors for motors controlled by soft starters is no different than sizing them for any motor controller, except VFDs. So you can't size it for less than 125% of the motor FLA from the NEC chart. You can size it for more if you like though...

VFDs are the only type of AC (squirrel cage induction) motor controller that has special rules for conductor and OCPD sizing, and that is just 125% of the VFD Max Amp Rating, not the motor connected to it.
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FLA of the motor. Sorry should have been more clear. I've alway's sized them 125% of the FLA of the motor, but was challenged by a coworker that you have to size them to the size to the soft start. But I explained to him that you have to set you ocp of the motor in a parameter setting in the soft start. I think he is getting confused with a VFD.
 
patriot said:
... I think he is getting confused with a VFD.
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Looks like it to me, a lot of people get confused on the difference. The VFD circuit sizing rules were added in the 2005 NEC, and changed again in 2008, so forsome this is still relatively new. Many people tend to over apply new rules for a while.
 
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