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Old 02-08-2012, 12:33 PM   #1
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Older Romex / NM 14-2 proper grounding


Hello! New here and hoping to gain a little knowledge of proper application of the NEC, as a DIY'er. First question that I would like to pose and have done some research on:

My house has older style romex with the tar/weave outer jacket. Metal boxes. Copper wire. I have been changing outlets from the older two prong style w/o ground to the 3 prong style with ground.

Some outlets (Kitchen) are 12-2. The majority of the others are 14-2. In either case the ground wire is undersized, ie. 14-2 + 16 ground, or 12-2 + 14 ground.

Far as I can tell, unless running a new branch circuit, this was the code at the time so acceptable to continue using now. And since the ground wire is only supposed to be used briefly during a fault condition, it should not heat up to dangerous levels before a breaker trips. To further guarantee safety, in places where a GFCI is appropriate or called for I have used them.

But one situation particularly sticks out in my mind. Am I opening myself up to liability if someone plugs in a 3 prong extension cord with a switched ground/neutral -- thus making the undersized ground the primary path back to the panel? That would pose a real potential issue!

Thanks for any advice -- seems that it would generally be safer to wire the outlets as 3 prong with ground to avoid a shock hazard, but the trade off is fire hazard in the event of a neutral fault!

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Old 02-08-2012, 12:49 PM   #2
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Older Romex / NM 14-2 proper grounding


Wire the outlets properly and go on with life.

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Old 02-08-2012, 01:04 PM   #3
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Older Romex / NM 14-2 proper grounding


The GFCI will provide proper protectoin for people with or without the ground.

I would connect up the ground wires as if they were correctly sized.

Incidentally a GFCI will trip before more than a few milliamperes (let alone enough amperes to cause overheating) take the ground wire as the path back to the power source due to a fault.

What is a switched ground-neutral cord? A cord with a fault between neutral and ground should be discarded.
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Last edited by AllanJ; 02-08-2012 at 01:15 PM.
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Old 02-08-2012, 01:10 PM   #4
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Older Romex / NM 14-2 proper grounding


People sometimes do weird things with extension cords, such as cut the ends off or insert a splice. If the replacement end is miswired by connecting the ground in place of the neutral, the circuit will still function but the load will now be traveling down the thinner gauge ground wire instead of the normal gauge neutral wire.

Same issue if an appliance has ground and neutral tied together, and a fault develops on the neutral wire. The ground wire will still provide a path back to the box but it is now underrated to handle the current. This is probably one reason the NFPA revised the code.
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