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I'm in the United States. I have a handful of three-prong outlets that have been grounded to the underground water main just as it enters the crawlspace. All of the ground wires are home runs to the same clamp on the water main. This rules out ground-to-ground potential differences but maybe not ground-to-neutral differences, since I believe the panel is coupled to the water main only through dirt.

It's my understanding (correct me if I'm wrong) that the ground terminal on GFCI outlets can safely be left unconnected as long as the cover plate is marked "NO EQUIPMENT GROUND." Is this safer than the existing plumbing-ground situation I described?

I realize that neither choice is ideal, but replacing all of the 14-2 NM with modern 14-2/WG isn't an option at the moment.

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  • How is the panel grounded? Assuming there are ground rods in the soil, how close are they to the water main, and how is your soil?
    – Jay Bazuzi
    Jul 24, 2012 at 3:31
  • The panel is modern and has two separate ground rods. They are about 20 feet from the water main. The soil is clayey.
    – ArgentoSapiens
    Jul 24, 2012 at 15:32
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    My vote would be for GFCI with no ground. GFCI will eventually trip when there is a ground fault, and should prevent you from being killed. With no GFCI and receptacles bonded to water pipe, the ground fault might not kill you but it might kill the plumber holding the pipe while standing in a puddle.
    – Tester101
    Jul 24, 2012 at 16:44
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    GFCI with no ground is way safer than non-GFCI with ground, even if the grounding is completely code-compliant. GFCI is meant to protect humans against electrocution. If there is a voltage imbalance between the hot and neutral sides of the outlet, meaning that electricity is bleeding off through some other path (your heart, for instance), the GFCI trips. The ground wire serves a somewhat different purpose and isn't necessarily a guarantee against electrocution. Likewise, GFCI doesn't provide any grounding for equipment plugged into it, unless the GFCI itself is grounded.
    – Craig Tullis
    Nov 28, 2014 at 22:41
  • As of NEC 2014, it's now legal to retrofit just a ground wire, going back to the same panel the circuit is served out of. So go to town. Two circuits (out of the same panel) can share a ground. Your plumbing ground point sounds fine, but it must go first to the ground bus of the main panel and be bonded to neutral there (only). Ground and neutral bus can be combined in the main panel only, not in subpanels. Circuit grounds should go to the main panel, not the pipe.
    – Harper - Reinstate Monica
    Jan 25, 2017 at 2:14

3 Answers 3

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This is not even a contest. A non-GFCI outlet will happily send 1A through hot, into a faulty or misused appliance (think: submerged toaster), from there through you into some other ground (any ground will do, it doesn't have to be that same appliance's ground), without noticing anything's amiss. You, meanwhile, are dead several times over. The ungrounded GFCI-protected outlet, OTOH, trips as soon as the current imbalance reaches 30mA or so. If all the current leaving the GFCI eventually returns, there's none left to be going through your heart.

Yes, the GFCI could fail to open when it should (so test it regularly), but the counter-objection is that having a ground on the outlet doesn't guarantee that the circuit breaker will operate when a loose wire in an appliance touches the chassis. This is why my local electrical code doesn't like the idea of a single failure causing harm, so all socket outlets must be both GFCI-protected and grounded. For some reason I don't quite understand, lighting fixtures are exempt from this, as are stoves/ovens.

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  • It sounds like you're proposing to abandon the retrofit ground wire. Is that correct? It is of less than no value?
    – ArgentoSapiens
    Jul 24, 2012 at 19:03
  • Not sure I understand... I'm sticking to the brief of the question: choose the lesser of two evils.
    – Bernd Jendrissek
    Jul 24, 2012 at 19:24
  • I appreciate the directness of your answer. And I do like the idea of abandoning the janky retrofit that someone else did.
    – ArgentoSapiens
    Jul 24, 2012 at 20:13
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Ground and neutral should be tied together at the main panel.

A GFCI will trip when it detects a current imbalance between hot and neutral. This means that current imbalance may go through your body for a short time. It's not likely to hurt you but there it is.

A grounded outlet should trip the associated breaker if hot ever touches ground. No current would go through your body if you were not touching the equipment.

That's if everything works as intended. There are failure modes that could increase the chances of you being hurt. For example, if the ground wire is broken somewhere, you might not know until it is too late. Likewise if the GFCI protection failed, you might not know either.

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  • Agreed, but in this case the ground wire does not go near the panel.
    – ArgentoSapiens
    Jul 23, 2012 at 22:45
  • In that case, what you have can not be considered grounded for safety reasons and your answer is use the GFCI.
    – Philip Ngai
    Jul 23, 2012 at 22:52
  • Better might be to run a ground wire from the panel to the same clamp. Nowadays the clamp should be within the first 5 feet of the water pipe's entering the building. The panel should also be grounded via an independent grounding electrode.
    – Jeremy W. Sherman
    Jul 23, 2012 at 23:27
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    @JeremyW.Sherman Right. But you are now making the water pipe a grounding electrode (250.52(a)(1) now applies), and the wire you run from the panel to the pipe would be a Grounding Electrode Conductor. As you say it might only have to be #8 copper, but you can't just use #14 from the pipe to the panel. The only point I'm trying to make, is that the wire has to be sized accordingly.
    – Tester101
    Jul 24, 2012 at 16:54
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    @Tester101 Yours is the first mention of #14 I've seen. I took for granted that the grounding conductor would have to be sized appropriately. When using a water pipe, the requirement to have a supplemental electrode also applies (250.53(D)(2)). But just grounding to the water pipe would be a huge improvement.
    – Jeremy W. Sherman
    Jul 24, 2012 at 17:05
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Is the pipe under ground galv steel or plastic? Assuming it is metallic pipe to a metallic box where the outlets are to be installed, you can run a green ground jumper from the box to the ground terminal on the GFIC. I would then be absolutely sure to run a #4 Copper bonding conductor from the panel ground to the water pipe in the house with an appropriate connector.

Regardless, always use GFIC outlets outdoors. They will work without the ground connected, but the extra work of bonding/grounding the boxes and outlets is worth the effort.

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  • The pipe is copper and the retrofit ground wires go all the way into the boxes and to the ground terminal on the receptacles.
    – ArgentoSapiens
    Jul 24, 2012 at 15:33

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