Enclosures, disconnect levers, and contactors

[megloff11x]

For a machine that is mainly motors and motor controllers, the NEC requires that the enclosure for AC distribution cuts power when its door is opened. They also like you to be able to lock out the equipment.

Do you have to use an enclosure with the built-in lever, or can you mount a simple switch to the inside of the door that opens when the door opens, and run this through the contactor loop for the start & stop buttons?

You have to have the contactor anyway to put remote stop buttons near those motors that can grab & chew the reckless, should they decide to remove the covers and poke around.

Why have two disconnecting devices in series, a lever and a contactor?

If you open the door, power is off and stays off until that switch is reset and the start button is pressed. I found some breakers that allow a lock-out, albeit with a padlock like the one you find on a cheap suitcase.

Let me know. Is there any key part of the code missing from this method?

 

[jim dungar]

Re: Enclosures, disconnect levers, and contactors

The NEC does not require that all power be "cut" automatically when a door is open.

The NEC does allows one disconnecting means for the power supply and a separate disconnect for the control circuit. Most of the time, however, the control circuit disconnect is an interlock on the power disconnect.

There are several exceptions to the requirement for a control power disconnect.

 

[tom baker]

Re: Enclosures, disconnect levers, and contactors

The disconnecting rules for your application may not be in the NEC, but rather in UL 508 Industrial Motor Control or NFPA 79, Machine Tools (?).NFPA 79 is similar to UL 508, but far less expensive to buy.