Motor Control and 2nd Motor disconnect

[frbrux]

Mike,

I have a question concerning the motor disconnect means, whether or not this is required by codes and standards to be interlocked with the motor controller circuit, when the second disconnect (the motor disconnecting means) is required to meet the 50 foot ruler. The Controller disconnecting means is not lockable, out of sight, and more than fifty feet away. Also, if an aux contact in the motor disconnect is required to be interlocked with the motor controller circuit to prevent possible unexpected start up when the motor disconnect is closed, would lockout tag out procedure permit this interlock (providing it is required) to be omitted? Or would the motor disconnecting means be required to disconnect the control power in its entirety to the motor control circuit via an additional contactor at the controllers control power transformer or by two aux contacts within the motor disconnecting means.

I have heard of situations of motor disconnects being closed and motors inadvertently starting because someone initiated the start command (pressing the start button and walking away), Later when maintenance is complete the motor disconnect is closed and the motor immediately starts.

What are your thoughts?

Motor in Question:

10 Hp, 3-Ph, 460 V

Part of a multi-motor process

Industrial environment

Multiple stop start locations.


Thanks for your time,

Frank Brux

Edited to remove your e-mail address and phone number. Please use the PM (private messaging) system and trade e-mail address and/or phone numbers there.

Thanks,
Charlie

[ November 29, 2004, 12:54 PM: Message edited by: charlie ]

 

[rbalex]

Re: Motor Control and 2nd Motor disconnect

The rules for the motor control circuit disconnects are rather complex. They are found in 430.74

From your description:

1.) The motor disconnecting means [430.102(B)] is not ?in sight? of the controller disconnecting means [430.102(A)] and the Exception to 430.102(B) does not apply.

2.) The motor control circuit disconnecting means is not automatically opened when either the motor or controller disconnecting means is opened.

3.) It is not clear whether the installation meets the basic 430.74 rule or either of the two Exceptions.

In any case, the motor disconnecting means is not required to be lockable, is it not required to disconnect any thing other than the motor branch circuit conductors and it is not required to be interlocked with anything.

Lockout-Tagout rules would be in effect under an NFPA 70E hazard analysis at each "start/stop" location to caution workers to avoid initiating a start sequence where it was determined that reclosing the motor disconnect creates a hazard.

You may also need to review 430.113 for other potential issues.