Motor controller disconnect

[petersonra]

to qualify as a motor controller disconnect does the disconencting means have to:

A. Disconnect power to the motor starter coil?

B. Disconnect power to aux contacts such as overload or running contacts?

My contention is yes to both, but the NEC definition is ambiguous enough that one might argue otherwise.

 

[petersonra]

no one wants to take a stab at this?

I actually managed to stump you guys?

 

[augie47]

My contention is "both" also.
The only ambiguity i find in applying 430.75 is that many controllers use the grounded conductor as the portion of the control circuit going to the OL relay and I see no reason for disconnecting that.

 

[templdl]

My contention is "both" also.
The only ambiguity i find in applying 430.75 is that many controllers use the grounded conductor as the portion of the control circuit going to the OL relay and I see no reason for disconnecting that.

Using an MCC as an example, the bucket contains either a fused disconnect or a breaker more than likely an MCP. The combination starter is disconnected by simply moving the handle operator to the OFF position. Since it is common for the control power to be 120vac the combination starter is provided with a CPT located on the load side of the disconnect within the bucket itself and, as such, the control power will also be disconnected when the disc. Sw. is placed in the OFF position. . Should the control power be supplied from a separate source there is usually a electrical interlock provided of the handle operator which will disconnect the power from the separate source.
In addition, should it also be addressed that there should be a disconnect for the motor at or within sight of the motor should the motor controller be located in a remote location?

 

[don_resqcapt19]

I don't see control circuits as "supply circuits" to the controller and 430.103 requires the disconnection of all ungrounded supply conductors. There is a reference to 430.113 but that also appears to apply only to the motor power circuit and not the control circuits, however, based on Exception #2, it appears that the CMP intended it to apply to both the power and control circuits. If that is the case, the code language does not support that intention.

 

[augie47]

Don, does 430.75 not cover that

 

[petersonra]

I asked because it seems ambiguous to me.

Ambiguous means that the AHJ gets to decide what it means, at least as a practical matter.

Is there some way to get the NFPA to make some kind of ruling on matters of ambiguity? It seems like in the past they have often responded to changes that have eben suggested to remove such ambigutiy by stating there was no ambiguity.

 

[don_resqcapt19]

Don, does 430.75 not cover that

I don't see anything that says the disconnect that is required by 430.102 for the motor controller has to disconnect the control circuits. Yes, the control circuits have to have a disconnect, but original question was if the motor controller disconnect also has to disconnect the control circuit, and that is not what the code requires. The code permits, but does not require the motor controller disconnect to disconnect both the power and control circuits.

 

[templdl]

I don't see anything that says the disconnect that is required by 430.102 for the motor controller has to disconnect the control circuits. Yes, they control circuits have to have a disconnect, but original question was if the motor controller disconnect also has to disconnect the control circuit, and that is not what the code requires. The code permits, but does not require the motor controller disconnect to disconnect both the power and control circuits.

I know that on MCCs with separate source conrol we placed a yellow label on the bucket stating as such. Sort of CYA.