Disconnects & VFD's

[lghtning4u]

A situation has come up involving wither or not a disconnect must be provided before and/or after a VFD that includes a disconnect in it.

Based on 430-103 & 430-128 I say a disconnect is not required if the VFD has its own disconnect and is within site of the equipment.

Do you agree?

 

[pfalcon]

Correct

430.102(A)
There must be a disconnect for the controller within sight of the controller.
430.102(B)
There must be a disconnect for the motor within sight of the controller.
430.102(B)(2)
Permits the controller disconnect to do dual service as the motor disconnect providing it meets the requirements for both.

You will not find any prohibition against integral disconnects.

 

[DPW]

Vfd disconnect

Vfd disconnect

Is the VFD's disconnect sufficient if the VFD controls several motors? Or can the individual manual motor starters (inside the VFD panel) serves as the individual disonnecting means?

 

[buldogg]

Correct

430.102(A)
There must be a disconnect for the controller within sight of the controller.
430.102(B)
There must be a disconnect for the motor within sight of the controller.
430.102(B)(2)
Permits the controller disconnect to do dual service as the motor disconnect providing it meets the requirements for both.

You will not find any prohibition against integral disconnects.

Also note, the exception to 430.102 states that in industrial installations with written safety procedures the motor disc. is not required if the controller disc. can be locked in the open position.

 

[pfalcon]

Is the VFD's disconnect sufficient if the VFD controls several motors? Or can the individual manual motor starters (inside the VFD panel) serves as the individual disonnecting means?

Provided you meet 430.103 through 430.109 (proper operations) and
provided you meet 430.102 (all sight requirements) and
provided the device is approved for use as a disconnecting means (typically listed) and
provided you meet NFPA70E (safety protocols) then
typically any upstream disconnecting means on the same machine qualifies.

Motor starters are not typically listed for use as a disconnecting means. Further they typically do not include a means for LOTO procedures. Therefore they fail twice.

buldogg mentions 430.102(B)(2)(b) permitting industrial sites to use the controller disconnect under certain conditions. Since OSHA effectively mandates NFPA70E, all those conditions are required by industry to be met for a controller disconnect anyway. The same conditions for the controller under NFPA70E are required for both the motor disconnect and the main panel disconnect.

There is no restriction to the number of motors or controllers under a disconnect other than that they must be on the same machine 430.102

 

[George B.]

VFD Disconnect

VFD Disconnect

Your original question was is a disconnect required before or after the VFD and as 430.128 says "shall be permitted" this is not a mandatory rule. Considering that the VFD has a disconnect within the unit another disconnecting means isn't necessary. Something else to keep in mind is the interrupting rating of the supplied breaker as stated in 110.9 (Is it able to handle the fault current available at the line terminals?)

 

[cowboyjwc]

Within 50'?