Do I ground to box or back of outlet?

Old 03-10-01, 01:05 AM
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I just moved an outlet in my house by installing an
extension box on the original box and then using EMT
conduit to run wires from the wires in the wall to a new box on the other side of the room.
In this other box I installed an outlet. There is a ground
screw on the back of the outlet; that's where I attached
the ground wire. So the wire comes out of the wall, then
splices directly to the new fresh wire using wire nuts
( white to white, green to green, black to black ) then
the new wire runs through conduit to another box. In this
new box the ground is attached to the back of the plug.

Is this right ??
OR, should I have attached the ground to the BOX instead?
OR, should I have attached it to the first extension
box where the wires used to terminate, and also attached
it to the final box?
OR, should I have attached it to BOTH boxes and the ground
screw on the back of the outlet?

Which is the correct way??

Note I just have lamps plugged into the new outlet.

Also, could someone please explain why one method would be
more "grounded" then the other? My electrical book showed
to ground on the outlet and the box, but my boxes don't have
grounding screws, so how would I do it anyway??

Lots of questions, sorry.

Thanks for any help

Old 03-10-01, 01:08 AM
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Note, the 3-pronged tester I plugged into the new outlet
shows that it is grounded correctly. But is it possible
for the outlet to be grounded without its containing box
being grounded?? I'm afraid to touch the outside of the box
now. Am I over analyzing this? How does grounding work?!?

Old 03-10-01, 05:33 PM
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Both the box and the receptacle green screw should be bonded to the green or bare wire if the box is metal. There is a threaded hole in the back of your steel box that is designed to accept a green grounding screw. You are to pigtail the green or bare wire with a wire nut so that two pigtails come out of the wire nut one for the box one for the receptacle. Also if you connected to a junction box that is metal and has a blank plate then that metal junction box is also supposed to be grounded with a bare or green wire using the threaded hole and a green grounding screw.

The reason for both the box and the receptacle being with a green or bare grounding wire is the unreliable connection of you receptacle yoke that mounts the receptacle to the box with two 6/32 scews. There is such a thing as a self grounding receptacle that you may use instead of attaching both box and receptacle with a grounding wire. This self grounding receptacle has an attachment on the yoke of the receptacle that is spring loaded designed to ensure reliable contact between the yoke of the receptacle and the metal box.

A green or bare wire is an equipment grounding conductor. This is a path that is not designed to be energized except when there is a short circuit fault. When a fault happens then there is a signal or current that flows momentarily on that bare or green wire back causing the breaker to kick for a second reason called a branch circuit breaker interupting rating. This interupting rating is set rather high in current to cause a reliable service of power to you utilization equipment but is designed to shut off due to the interrupting rating if a short circuit happens.

A short circuit is when voltage flows to metal not designed to be energized such as the metal frame of a washer, refrigerator, stove, steel boxes, metal siding etc. Any non electrical metal is designed to be protected for inadvertantly being energized for any length of time due to the protection of that equipment grounding conductor.

A breaker kicks off due to two reasons. Too many amps being pulled on the conductor of a circuit which is designed to protect buildings from fire. The second reason is the short circuit interupting of the breaker due to metal becoming energized that is not supposed to be energized. This second method protects people and uses that bare or green equipment grounding conductor to protect those people who may be exposed to electrical shock due to metal being enegized that is not supposed to be energized.

Hope this helps

Old 03-10-01, 09:06 PM
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Great, thanks! You answered everything I needed to know.
It looks like I have a little bit of work left.


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