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Grounding metal boxes on GFCI circut

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Grounding metal boxes on GFCI circut Red Green 04-26-2008
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Posted by Red Green on April 26, 2008, 10:39 pm
Here;s a situation I came across.

I know any time a metal mounting box is used for a duplex outlet the box
should be tied to the ground wire coming in.

What if the metal box/outlet is on the load side of an upstream GFCI?

Maybe codes say it still has to be grounded (?) but from a safety
standpoint is it pointless to ground the metal box?

Posted by BobK207 on April 26, 2008, 10:45 pm
> Here;s a situation I came across.
>
> I know any time a metal mounting box is used for a duplex outlet the box
> should be tied to the ground wire coming in.
>
> What if the metal box/outlet is on the load side of an upstream GFCI?
>
> Maybe codes say it still has to be grounded (?) but from a safety
> standpoint is it pointless to ground the metal box?

Metal boxes should always be "grounded".

cheers
Bob

Posted by Tony Hwang on April 26, 2008, 11:18 pm
Red Green wrote:
> Here;s a situation I came across.
>
> I know any time a metal mounting box is used for a duplex outlet the box
> should be tied to the ground wire coming in.
>
> What if the metal box/outlet is on the load side of an upstream GFCI?
>
> Maybe codes say it still has to be grounded (?) but from a safety
> standpoint is it pointless to ground the metal box?
Hi,
Floating metal box is not a good idea. If hot touches the box you can
get zapped.

Posted by RBM on April 27, 2008, 7:09 am

> Here;s a situation I came across.
>
> I know any time a metal mounting box is used for a duplex outlet the box
> should be tied to the ground wire coming in.
>
> What if the metal box/outlet is on the load side of an upstream GFCI?
>
> Maybe codes say it still has to be grounded (?) but from a safety
> standpoint is it pointless to ground the metal box?

It must be grounded, gfci or not.



Posted by Wayne Whitney on April 27, 2008, 11:43 am

> What if the metal box/outlet is on the load side of an upstream
> GFCI? Maybe codes say it still has to be grounded (?) but from a
> safety standpoint is it pointless to ground the metal box?

As others mentioned, the NEC requires it to be bonded (connected to an
EGC). And there is an advantage to this even when the conductors are
GFCI protected.

Suppose the hot conductor faults to the box. If the box is bonded,
this will immediately create a short circuit and trip the circuit
breaker or GFCI. If the box is not bonded, nothing will happen until
you come along and complete a circuit with your body. If your body
connects the box to ground, this will trip the GFCI; but if your body
connects the box to neutral, it won't trip. Moreover, the hot
conductor to box fault could persist for a long time, long enough for
a second failure to occur, such as the GFCI going bad. Then there
would be nothing to protect you.

Cheers, Wayne

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