Line Power for industrial controller

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I have a question about the practices used in industrial wiring. I
work with indusrial control systems and often I see industrial panels
wired with the line power wired "straight through" the enclosure. By
"straight through" I mean the cord passes through a hole drilled in
the enclosure. There is strain relief and a metal ring (perhaps for
EMI and for a good seal) where the cord enters the enclosure. The
enclosures are usually the water resistant type (NEMA 3 or better) and
on the male end of the cord is the plug for going into the 110, 220,
400, or whatever the supply voltage is.

Does anybody know why this practice is used? I've seen it most in the
U.S.A. I see that it protects agains accidentally unplugging at the
enclosure (there is no bulkhead and connector there, but pulling on
the cord will still unplug it at the plug end. Additionally, I see
that it could be dangerous if the strain relief failed and the wires
were pulled out of the terminals inside the panel (possible short).

Any ideas?

-SDS

 

You will notice that most wiring in metal boxes has those bushings on it,
even in your house. They prevent the wire from moving, without pinching the
conductor. If you didn't, then among the less desirable results would be
the insulating being abraded off, and a bit of arcing to the box at that
point.

Michael