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When to use disconnect

When to use disconnect

When to use disconnect

I am installing a new control panel right next to an existing panel.  I would like to branch the existing panel's 480vac power from the line-side of its door-mounted disconnect, to provide power to the new panel.

The new panel has a subpanel mounted main breaker, but is a door-mounted disconnect required?  When would it be?

The new panel provides 480vac power to several <3hp motors and a CP Xfmr for 120vac control power.


RE: When to use disconnect

A disconnect is required for the panel only if it is also serving as the motor controller.  See 2002 NEC 430.102(A).  If it is not the controller, then a local disconnect is not required for the panel, only upstream overcurrent protection.

Disconnects are probably required for the motors, but this depends on exact installation details.  The panel may or may not be a suitable location for motor disconnect, again, depending on the exact installation details.  See NEC 430.102(B) for motor disconnect requirements.

Pay attention to the Exceptions for both 430.102(A) and (B), these exceptions are widely used.  Also, note that these requirements were SUBSTANTIALLY revised in the 2002 NEC.

RE: When to use disconnect

Is there a reason why you don't supply the power after the main disconnect device ?

As long as the second panel requires a tool it shouldn't be an issue but you must identify any live circuits after the main disconnect is shut off. The main panel and the secondary panel must warn the service person that live circuits still exist. If the panel can be opened without the use of a tool you must have a disconnect device interlocked with the door.

Christopher Caserta

RE: When to use disconnect

Oops, this is the second time now that I've posted an NEC answer to an IEC question.  Forget what I said.  I gotta start paying more attention to which forum I'm in.  Sorry.

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