VFD, Motors, & Motor Starter Disconnecting Means

[djr3203]

My office had a tech seminar with a VFD and Combination Motor Starter Manufacturer today, which sparked some debate within the office. I thought I would take this debate to the online community.

The manufacturer was exhibiting their Motor Starter package, which included a disconnect switch at the top that can be locked off, a motor starter below it, contacts below that, and solid state overload protection below that. The following was the question that sparked the debate.

Can the disconnect switch within the motor starter function as the disconnect switch for the motor starter (considered a controller) or does the NEC require an additional, external disconnect for the motor starter (controller)?

My research has lead me to the following observations.

1. NEC 430.102(A) requires a disconnect for a controller (which covers motor starters and VFDs)
2. NEC 430.102(B) requires a disconnect for a motor
3. NEC 430.102(B)(2) allows the disconnect for the controller to function as the disconnect for the motor if it is within sight of the motor
4. NEC 430.103 allows the disconnecting means to be permitted in the same enclosure with the controller.

So, it seems to me that the disconnect in the controller can function as the disconnecting means for the controller and motor as long as the controller is within sight of the motor. Is this correct?

The other side is that since the disconnect is inside the controller, the lugs will still be "hot" and could still present a shock hazard when performing maintenance on the controller.

All input is welcome!

DJR

 

[SteveWag]

The disconnect may be inside the controller enclosure, hence combination motor starters and MCC’s. A special motor disconnect is not required if the controller disconnect has integral locking capabilities under two exceptions; 1, motor disconnect is not practical (well pumps, VFD controllers, etc) 2, where LOTO practice is written and established.
Steve

 

[rcw retired EE]

Your understanding is correct. The disconnect in the Combination Motor Starter enclosure can be considered the disconnecting means for the starter and motor.

Note that the exception in 330.102 (B)(2)(b) allowing the disconnect to be out of sight of the motor is probably used by 80% of the industrial applications.

 

[jraef]

Nothing to add on the other responses, but to this point:

The other side is that since the disconnect is inside the controller, the lugs will still be "hot" and could still present a shock hazard when performing maintenance on the controller

Yes, it will. So if the facility has a need to do "hot work" on this controller, then they will need to don the appropriate PPE after taking out a Hot Work Permit per their established and documented procedure (as now required by NFPA 70E). Or they could use a separate lockable disconnect switch up stream in a different enclosure.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376