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Motor Disconnects, Part 2

Motor Disconnects, Part 2Any disconnect you use with a motor must open all of the ungrounded supply conductors, and it can’t permit independent operation of any pole [430.103]. Nor can the disconnect be closed automatically. It can, however, be in the same enclosure as the controller.

The disconnect must also plainly indicate its position [430.104]. A common means of doing this is inherent in the construction of a common type of disconnect. If you look at the typical disconnect for a 10 horsepower industrial motor, you’ll notice it has a big red-tipped handle on the right-hand side. This handle is up when the circuit is closed, and down when it’s open. The cover of the disconnect typically has embossing or a sticker with ON in large letters at the top and OFF in large letters at the bottom. You can easily tell which position it’s in.

One mistake with this style of disconnect is a misconception of how it’s intended to be operated. Some people will stand in front of it and operate the handle with their right hand. The correct way is to stand to the right of the switch and operate the handle with your left hand; this puts you out of the path of an arc blast. Keep this in mind when choosing a mounting location near a corner.

Note that there are many other types of disconnects, including variations of a rotary switch style.

« Part 1 | Part 3 » | Source: Mark Lamendola | Mindconnection