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Old 05-13-2012, 11:44 AM   #1
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Acceptable way to ground metal box?


Hello all,

Is this an acceptable way to ground a metal box, by looping the main green wire around the green screw as that wire enters the box? (as shown in the picture) Or is it more correct to just run a pigtail to the green screw? With the method I've shown, it saves me from making another pigtail, and then it's easier to twist, say, three wires in a wire nut instead of four.

http://postimage.org/image/j2ll14jiv/

Any reason why this method is wrong or a bad idea? Thanks.
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Old 05-13-2012, 11:58 AM   #2
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Acceptable way to ground metal box?


It is fine as long as the wire is not crossed under the screw, that would be a bad connection and damage the ground wire. Maintain a tight U shape.

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Old 05-13-2012, 12:03 PM   #3
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Acceptable way to ground metal box?


so you're saying, as long as the ground wire doesn't touch itself as it loops around the screw?

Just curious, why would that make a bad connection, if the ground wire touches itself?

Also, is this the way an electrician would ground a box, or would he use a pigtail? thanks again.

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Old 05-13-2012, 12:08 PM   #4
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Acceptable way to ground metal box?


You can loop it around the screw and, instead of crossing over, the wire bends back the other way and continues on to something else. Some folks call that an omega shaped loop. The wire must not be bent too sharply, thr bending radius around the screw is a good enough minimum to go by.

Wrapping around a screw and then continuing to something else is not that common because most of the time the ground wire end is not long enough.
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Old 05-13-2012, 12:22 PM   #5
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Acceptable way to ground metal box?


OK, so then the way I've looped the wire in the picture would not be ideal, since the wire crosses over and is bent farther than a U shape.

I can understand that bending the wire too far might make it brittle, but does it create a safety hazard in some other way? thx.
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Old 05-13-2012, 01:04 PM   #6
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Acceptable way to ground metal box?


The "bad" connection is because the screw hits and tightens on the spot where the wires cross and does not contact the rest of the loop. The connection is not "that" bad. The problem is that the wire gets crushed where it crosses and after years of vibration from trucks passing on the street outside, the wire could break.

Simply bending the wire farther than a U shape does not weaken it, it is how sharp the crease is.
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Old 05-13-2012, 01:59 PM   #7
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Acceptable way to ground metal box?


Quote:
Originally Posted by AllanJ View Post

Wrapping around a screw and then continuing to something else is not that common because most of the time the ground wire end is not long enough.
Actually it is quite common in new construction.
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Old 05-13-2012, 02:31 PM   #8
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Acceptable way to ground metal box?


I usually just use a scrap piece of bare or green insulated wire to go to the screw then wire nut all the grounds together. But I have done it both ways.
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Old 05-13-2012, 04:04 PM   #9
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Acceptable way to ground metal box?


if i'm running the cables, i try to do just this.

but i'll use a pigtail if necessary

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