Disconnection 430-73 in 2005 NEC

[t_rhea]

An engineer has rejected a custom designed motor controller with the following devices in question:
1-36"x36"x12" N4X enclosure
1- lockable disconnecting means for all circuits and control circuits within controller. (disconnect handle is accessible with enclosure door in the closed position-and disconnects main breaker located in enclosure)
1-motor starter located within enclosure (MCP breaker feeds motor starter and the main breaker feeds MCP breaker)
1-VFD located within enclosure (MCP breaker feeds VFD and the main breaker feeds MCP breaker)
1-control transformer located within enclosure is feed from main breaker

The following is the reason for the said code violation from engineering comments:

"As per article 430-73" he states that since each device cannot be disconnected from control voltage from by turning off the individual MCP breaker for each motor,starter motor, or VFD motor.

Please comment on the response that this scenario is an actual code violation or like I believe is that the engineer is just wanting to be able to use each individual breaker "after opening the door" to shutdown the associated controls in lieu of having to shutdown the entire system.
{Engineer is requesting for the function of being able to disconnect each MCP breaker and disconnecting each individual control circuit as he uses the MCP breaker to disconnect each individual load, so as not to disrupt the other motor circuit. Of course with no additional cost incurred to him.}
The design specifications were not calling for the installation of this fashion, the engineer in retro-spec, is trying to use the said code violation as a means to get this installed for free.

 

[jim dungar]

Re: Disconnection 430-73 in 2005 NEC

Short answer.
The NEC (and UL) requires the control circuit to have a disconnecting means. There is no requirement that the control circuit disconnect be operated at the same time as the motor power circuit.

In your case the control power transformer is disconnected when the main disconnected is operated thereby meeting the code requirements.

 

[john m. caloggero]

Re: Disconnection 430-73 in 2005 NEC

The 2005 NEC Section is 430.74. What the engineer is missing is that the Code gives permission to use two (2) disconnects, one for the motor and one for the control circuit. The second sentence is a permissive rule "shall be permitted" which means that the AHJ has to allow two disconnects. Section 430.101(B) the last paragraph makes it clear that an individual disconnect allows a single disconnect to disconnect both the motor and control.