VFD disconnect needs

[bgreenier]

what are the NEC requirements for disconnect needs for field mounted motor VFDs<

 

[petersonra]

what are the NEC requirements for disconnect needs for field mounted motor VFDs<

have you looked at 430.120 and beyond?

 

[carleaux]

I believe that motor-driven equipment must have a disconnect within line-of-sight. If you get a VFD with an integrated disconnect you should be okay.

 

[J. Hofstetter]

bgreenier,
Just a word of advice. If you do install a disconnect between the VFD and the motor, you should interlock the disconnect to the VFD so that if the VFD were running and someone throws the disconnect the VFD stops. I have personally seen VFDs grenade when they are outputting nearly full voltage and the disconnect is thrown in. A smaller drive may be ok, but larger drives, especially large drives with long motor leads have a tendency to blow the caps.

 

[don_resqcapt19]

The VFD is a motor controller and must have a line side disconnect within sight from the VFD. The motor also requires a disconnect within sight from the motor. If the VFD disconnect is also within sight from the motor you don't need a second disconnect. If the VFD disconnect is not within sight from the motor, you will need a second disconnect within sight from the motor, unless you installation meets one of the exceptions. 430.102

 

[kwired]

The VFD is a motor controller and must have a line side disconnect within sight from the VFD. The motor also requires a disconnect within sight from the motor. If the VFD disconnect is also within sight from the motor you don't need a second disconnect. If the VFD disconnect is not within sight from the motor, you will need a second disconnect within sight from the motor, unless you installation meets one of the exceptions. 430.102

Good explanation.

Though not enforceable part of code, I want to point out the informational note after that section mentions adjustable speed drives as being a potential reason to meet the exception. I would guess most AHJ would allow such exception to be used in this case.

 

[iceworm]

The VFD is a motor controller and must have a line side disconnect within sight from the VFD. The motor also requires a disconnect within sight from the motor. If the VFD disconnect is also within sight from the motor you don't need a second disconnect. If the VFD disconnect is not within sight from the motor, you will need a second disconnect within sight from the motor, unless you installation meets one of the exceptions. 430.102

Good explanation.

Though not enforceable part of code, I want to point out the informational note after that section mentions adjustable speed drives as being a potential reason to meet the exception. I would guess most AHJ would allow such exception to be used in this case.

How is it you come to the conclusion this is not enforceable?:?

The informational note is not discussing the disconnect for the controller. It is discussing using the controller disconnect for the motor disconnect.

However, if you are discussing only that part about not necessarily needing a motor disconnect if there is a VFD, then, I would point out, the informational note is the non-enforceable part.

ice

 

[kwired]

Originally Posted by don_resqcapt19
The VFD is a motor controller and must have a line side disconnect within sight from the VFD. The motor also requires a disconnect within sight from the motor. If the VFD disconnect is also within sight from the motor you don't need a second disconnect. If the VFD disconnect is not within sight from the motor, you will need a second disconnect within sight from the motor, unless you installation meets one of the exceptions. 430.102

Originally Posted by kwired
Good explanation.

Though not enforceable part of code, I want to point out the informational note after that section mentions adjustable speed drives as being a potential reason to meet the exception. I would guess most AHJ would allow such exception to be used in this case.



How is it you come to the conclusion this is not enforceable?:?

The informational note is not discussing the disconnect for the controller. It is discussing using the controller disconnect for the motor disconnect.

However, if you are discussing only that part about not necessarily needing a motor disconnect if there is a VFD, then, I would point out, the informational note is the non-enforceable part.

ice

What is your point, what you said is pretty much what I meant with what I said? Informational notes are not part of the code, which you seem be agreeing with.

All I was mentioning was that the exceptions allow for not having a disconnect at the motor for certain conditions but those conditions are not really that defined in the actual code. My comment meant to point out the informational note does mention that the VFD installation is a possible exception for whatever it means - it is still an informational note and not code.

 

[iceworm]

What is your point, what you said is pretty much what I meant ...

I read your post several times and I didn't get that. My bad.

ice

 

[kwired]

I read your post several times and I didn't get that. My bad.

ice

I'll let you go this time

 

[iceworm]

I'll let you go this time

Thank you

... All I was mentioning was that the exceptions allow for not having a disconnect at the motor for certain conditions but those conditions are not really that defined in the actual code. ..

For my work, the exceptions are well enough defined. I have only put in one disconnect "in sight of the motor" in the last 45 years. And that one was our choice - for maintenance convenience.

But I don't do commercial buildings either. Maybe the exceptions are not well defined for those applications - that I don't know.

ice

 

[kwired]

Thank you


For my work, the exceptions are well enough defined. I have only put in one disconnect "in sight of the motor" in the last 45 years. And that one was our choice - for maintenance convenience.

But I don't do commercial buildings either. Maybe the exceptions are not well defined for those applications - that I don't know.

ice

The general exception that used to apply to all installations allowed the controller disconnect to also be used as the motor disconnect if it was lockable. Worked real well on MCC's or other installs if the breaker was adjacent to the controller. I don't recall which edition of NEC eliminated that other than the few special cases still mentioned, but has been maybe 10 years or so since this changed so maybe 2002 or 2005?

If the controller is withing sight of the motor then not a problem cause both the controller and motor require a disconnect but one disconnect can serve both if within sight of both.

 

[Aleman]

bgreenier,
Just a word of advice. If you do install a disconnect between the VFD and the motor, you should interlock the disconnect to the VFD so that if the VFD were running and someone throws the disconnect the VFD stops. I have personally seen VFDs grenade when they are outputting nearly full voltage and the disconnect is thrown in. A smaller drive may be ok, but larger drives, especially large drives with long motor leads have a tendency to blow the caps.

That is true. We have started using local motor disconnects that have an early break interlock switch built in so the VFD will shut down before the mains shut off.