NEC Issue - Local Disconnectors

[BECREZ]

This question concerns compliance with Article 430.102(A) for disconnecting means for a motor controller where the controller is integral to a component such as an MOV, yet the disconnecting means resides at the MCC and not within sight and when opened will disconnect power to the motor and controller. Note that this is for an installation less than 600 volts.

By Article 430.102(B), an MCCB at a MCC qualifies as a disconnect for a motor on a MOV because it is capable of being locked in the open position, and the facility uses a lockout-tagout procedure and is maintained and operated by qualified personnel.

By Article 430.102(A), it would appear that another disconnect would be required at the MOV to satisfy the requirement for a controller disconnect.

1. Since the MCCB is a qualified disconnect for the motor, is it not equally qualified to serve as the disconnect for the controller at the MOV? (Control power for the controller is derived internally at the MOV from a control power transformer connected to the main line.)

2. In the above configuration, is an additional disconnect needed local to the MOV, if so why?

 

[dpc]

If the controller (motor starter) is at the MOV, as it often is, you must have a disconnect at the controller - there is no exception to this that I am aware of.

The exception you are referring to deals with situation where the motor controller is not within sight of the motor.

 

[BECREZ]

Thanks, but the issue here is why would a seperate disconnector be required local to the controller if the disconnecting means for the motor which is not within sighr (proper lockout/tagout procedures in place and with qualified personnel)and will cut the power supply off to the MOV entirely. I see no reason for it.

 

[dpc]

If you're talking about the NEC, there doesn't need to be a "reason", it just is.

The logic for having disconnect within sight of controller is to provide additional measure of safety to someone working on the motor starter that it will not become energized while his hands are in there. The only exception to this is for motors above 600V. This is one of the oldest provisions in the NEC section on motors.

There are a lot of things in the NEC that I see no reason for, but I still have to do them.

The basic rule is that there be a disconnect within sight of the controller and another disconnect within sight of the motor. Many facilities provide both in spite of NEC exceptions that eliminate need for local disconnect at the motor under certain conditions.

This exception was tightened up significantly in the 2002 NEC compared with earlier versions.

You always have the option of asking the AHJ for a variance, but I wouldn't get my hopes up.

 

[advidana]

NEC it is what it is.

 

[BJC]

The NEC every chapter and verse written by a committee. Proof that IQs add reciprocally.

 

[advidana]

yea but without it contractors would just install extendsion cords and flashlights.

 

[GOTWW]

What is MOV?, metal oxide varister? sorry.

 

[dpc]

GOTWW,

I assumed he was referring to a motor-operated valve.

 

[GOTWW]

We use solinoid valve, they pee on the ground abit, but they do not need a disconnect I hope.