Soft Starter and Isolating Contactor

[PowerQualityDoctor]

Do I need an isolating contactor when I install a soft starter or the main breaker is sufficient for complying with disconnection requirements?

 

[CFL]

You just need a means of disconnect not an isolating contactor. I think a bypass contactor and separate overload protection is handy depending on how critical the motor is. I just replaced a s.s. and added the bypass capability. It will allow maintenance to keep things going until repairs are made.

 

[don_resqcapt19]

Is the main breaker within sight of the soft start?

 

[PowerQualityDoctor]

The main breaker is within the sight.

Someone told me that soft starters are classified as motor controllers and not disconnectors and as such cannot be used for on/off the motor without contactors. Can you refer me to the relevant NEC section?

 

[don_resqcapt19]

I don't know of anything in the NEC that says a soft start or VFD has to have a set of contacts for the off/on control of the motor. Both items are motor controllers and all motor controllers require a line side disconnect within sight of the controller. It is correct that they are not disconnects.

 

[CIECO]

About 3 years ago I installed a MCC with 3 200 HP soft starts and after a month got a call from the customer that the only shut the motor off by pulling the disconect on the bucket. Not a big deal with a blower but with other machinery it could be. AS per nec no problem.