Grounding A 2 Prong Outlet - Electrical - Contractor Talk

Grounding A 2 Prong Outlet

 
 
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Old 05-13-2020, 01:00 PM  
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Grounding A 2 Prong Outlet


Home built in 1961. Original fuse, 2 wire system, metal boxes still in place throughout home.

I had an electrician tell me that if I add a ground wire to the back of the metal box that would ground the outlet and I could replace it with a 3 prong receptacle. Additionally, if I place a GFCI at the beginning of a run of outlets, that subsequent receptacles would trip the GFCI if faults occur.

I disagree with the grounding method.

I agree with the GFCI statement but only if the subsequent boxes are grounded.

From what I've seen, the metal boxes have no grounding back to the panel. I can see wires in the attic running to metal junction boxes but the wires do not have conduit around them. I'll get a picture of one of the 2 prong boxes but I have attached a picture of the wires coming up to the attic.

So my questions are:

1. Is that an effective grounding technique for 2 prong outlets?
If not,
2. Can an ungrounded outlet trip a GFCI?
If so,
3. Do we agree that subsequent boxes would trip the GFCI?
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Old 05-13-2020, 01:21 PM  
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Re: Grounding A 2 Prong Outlet


Is the wire NM or BX/MC?

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Old 05-13-2020, 01:33 PM  
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Re: Grounding A 2 Prong Outlet


Quote:
Originally Posted by aar0nhurst View Post
.....I disagree with the grounding method.
It may work, it may not. Depends on if the box itself is grounded.

Quote:
Originally Posted by aar0nhurst View Post
...I agree with the GFCI statement but only if the subsequent boxes are grounded....

Is a common myth that GFCIs need to be grounded to function properly. They never have been, and they never will need to be in order to protect against electric shock..

Fact is, if you use a GFCI device to protect downstream ungrounded receptacles, you are PROHIBITED from grounding them. 410.3(D)(3):

(c) A non–grounding-type receptacle(s) shall be permitted to be replaced with a grounding-type receptacle(s) where supplied through a ground-fault circuit interrupter. Where grounding-type receptacles are supplied through the ground-fault circuit interrupter, grounding-type receptacles or their cover plates shall be marked “GFCI Protected” and “No Equipment Ground,” visible after installation. An equipment grounding conductor shall not be connected between the grounding type receptacles.
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Old 05-13-2020, 01:35 PM  
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Re: Grounding A 2 Prong Outlet


Works off the neutral. Trips on an unbalance current.
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Old 05-13-2020, 01:39 PM  
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Re: Grounding A 2 Prong Outlet


Quote:
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Works off the neutral. Trips on an unbalance current.
GFCI's work off both the hot and neutral. If there's an imbalance, it will trip.
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Old 05-13-2020, 02:31 PM  
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Re: Grounding A 2 Prong Outlet


Wow! Great information and I appreciate it.

So as it sits today, no grounds are present in the wall outlets. The only ground that exists is at the panel. If I understand what I've read correctly, I can install a GFCI outlet without a ground AND that same GFCI will protect downstream outlets if current fault occurs? All without a ground?
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Old 05-13-2020, 03:28 PM  
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Re: Grounding A 2 Prong Outlet


Quote:
Originally Posted by aar0nhurst View Post
Wow! Great information and I appreciate it.

So as it sits today, no grounds are present in the wall outlets. The only ground that exists is at the panel. If I understand what I've read correctly, I can install a GFCI outlet without a ground AND that same GFCI will protect downstream outlets if current fault occurs? All without a ground?
If you can locate the first receptacle in the line and know how to identify the line & load conductors, you're golden.

One caveat, however: You may end up protecting more than just receptacles. Anything can be on that circuit. Over the years, stuff gets added, changed, moved, extended etc. So you might end up with either nuisance tripping, or the GFCI may trip and you lose power to something you don't want power turned off to (freezer, fridge, sump pump etc.)
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Old 05-13-2020, 04:18 PM  
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Re: Grounding A 2 Prong Outlet


If this is your house, it's a great time to take an afternoon and map out/label your circuits. It pays you back over and over again in the future.

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Old 05-13-2020, 04:33 PM  
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Re: Grounding A 2 Prong Outlet


Quote:
Originally Posted by 480sparky View Post
GFCI's work off both the hot and neutral. If there's an imbalance, it will trip.
Well ya... Has to check the imbalanced from something.

And that's the hot.
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Old 05-13-2020, 06:53 PM  
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Re: Grounding A 2 Prong Outlet


Quote:
Originally Posted by onmywayup View Post
If this is your house, it's a great time to take an afternoon and map out/label your circuits.
Quote:
Originally Posted by 480sparky View Post
One caveat, however: You may end up protecting more than just receptacles.
I called another electrician and plan to replace the fuses with breakers, upgrade from 100amp to 200amp service, and put a new mast on the house. I asked if he would map the circuits and he told me he would...as long as there weren't any rogue wires they can't find. Y'all were right on the money. Thank you.

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