metal cables with plastic boxes

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Old 06-17-09, 09:21 AM
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metal cables with plastic boxes

Can we discuss of what should be done in this situation if rewiring is not to occur?

My daughter's place has 2 wire BX, no ground, no continuous wire.

The box was metal, the outlet 3 prong, so it is likely that the ground prong was indirectly conducting to the sheath.

The box was replaced with plastic (the metal box was loose) , so I guess this is slightly better since the ground prong will not be a fire hazard (although it may be worse in the case that it could be a more likely electrical shock hazard)

But, I am guessing the better thing to do would be to put a GFCI outlet in the box, marking the outlet as "no equipment ground" with the included sticker. I am thinking this would better protect against fire and shock.

Would this be an acceptable thing to do?

Thanks,
Larry
 
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Old 06-17-09, 09:37 AM
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Old 06-17-09, 11:08 AM
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Metallic cables need to be used with metallic boxes. The plastic box should be removed and repalced with a metal one.

The ground pin only carries current on the event of a fault or short circuit. There should not be any current at any other time.
 
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Old 06-17-09, 02:21 PM
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Originally Posted by LarryNH914 View Post
The box was replaced with plastic (the metal box was loose) , so I guess this is slightly better since the ground prong will not be a fire hazard (although it may be worse in the case that it could be a more likely electrical shock hazard)
I certainly understand the logic in the switch to plastic box, however the code is pretty specific that metal boxes must be used with metal sheathed cables (BX/AC, MC). Even a poor ground is better than no ground, although the poor ground presents some problems too. I'm sure you've heard of the stories of red hot BX cable.

But, I am guessing the better thing to do would be to put a GFCI outlet in the box, marking the outlet as "no equipment ground" with the included sticker. I am thinking this would better protect against fire and shock.
Yes that's right. In fact you might even want to consider using a GFCI breaker instead as that will also protect all of the cabling inside the walls whereas a receptacle can only protect the downstream cable. The breaker is a bit more expensive ($30), but it does provide a small measure of added protection if you're not as concerned with the price.
 
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