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I have installed a sump pump in the basement. This house was made in the sixties so it has a two prong receptacle and does not have a ground wire available. I put a GFCI receptacle to plug the pump into, but I'd still like to have it grounded. So my question is this. Just outside this block wall, about a foot down, is ground. Could I drive a copper ground rod in there and just ground to it? It would sure be the far and away easiest solution.

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    Ah, the difference between grounding and bonding. Jan 2, 2022 at 0:40
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    Huh. Around here, 60's is late to not have any ground wire in the cable. It might be smaller than modern ground wires, but none at all is typically earlier than that, IME. Two prong outlet still quite common then. See if it got folded into the box clamp? Or: You wouldn't happen to be in one of the jurisdictions where everything's in conduit, rather than cables? If so, you have ground, without a ground wire. Take a clear picture of inside of the box and edit it in?
    – Ecnerwal
    Jan 2, 2022 at 0:55
  • I'll do that. Hopefully can get it done tomorrow. Thanks. Jan 2, 2022 at 20:27
  • I'm always concerned about putting a mission-critical device on a GFCI, without some sort of backup warning that something's gone wrong and tripped the GFCI without any sort of obvious alert. If the GFCI nuisance trips on your sump pump (which, according to many, happens often with a motor load), you may not notice. At a minimum, I'd suggest getting a water sensor and put its sensor a bit higher than where your sump pump would normally trigger, so if something goes wrong and the pump doesn't turn on as expected, you get an audible alarm you can act on, hopefully before your basement floods.
    – Milwrdfan
    Jan 4, 2022 at 17:22
  • OK. Went out there today. I ran a voltmeter from black to white on the GFCI receptacle and got 120 volts. I then went from black to bare ground. The ground is screwed into the back of the metal box. I got 120 volts there as well. I am taking that to mean the box is grounded by metal conduit. Sound right? I also want to say I remember my dad (this is his old house) talking about electricians at that time would just attach the bare ground to the metal box. I can't see where that was done on the inside but I guess it's possible. At any rate, does it sound like my ground is good? Jan 4, 2022 at 22:35

2 Answers 2

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Short answer, no you can't legally do that. But read to the end.

NEC 250.130 allows connecting a ground wire to an existing electrode, to the existing grounding electrode conductor, the ground bar in the panel where the circuit originates, to a ground wire that is part of another circuit originating in the same panel, or (yikes) to the grounded service conductor within the service enclosure (don't do that).

NEC 250.54 Allows auxiliary grounding electrodes that are connected to the equipment ground, they do not need to meet the full requirements for electrodes that are found in 250.50, but they must be connected to the existing system so that the earth does not become the current path for a ground-fault.

But now the bad news. The instructions with the GFCI say when installed without an equipment ground you have to put a sticker on the receptacle cover that says "No Equipment Ground". The reason for this is NEC 250.114 has a list of things that require an equipment ground that cannot use ungrounded receptacles. The instructions that come with those items will say to not use an ungrounded receptacle. Guess what? Sump pumps are on the list. You need connect that ground to one of the locations in 250.130 above or pull a new grounded circuit altogether.

Sorry.

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  • Thanks for the reply. Please note my reply to Harper above. I tried to copy/paste it but the site wouldn't allow it. Too many characters. Jan 4, 2022 at 22:39
  • If conduit is intact then that is an acceptable ground. It is best to run a ground wire from a 10-32 screw connected to the box to the receptacle, but depending on the box, cover and receptacle type it may not be required. Jan 5, 2022 at 1:39
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    Thanks for the reply. I ran a ground from the GFCI ground screw to a screw on the back of the box. I'm getting 120 volts on the voltmeter when I run from black to that ground. Jan 5, 2022 at 12:40
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Retrofitting ground should suffice

Run a ground wire, but not to two 8' ground rods driven into the earth. Instead run it back to the main service panel (or subpanel that the sump pump outlet is powered out of). #12 bare copper should suffice. It can follow any practicable route, and does not need to run with the circuit wires.

Instead of going clear back to the panel, you can also go to

  • any junction box which has a #12 or larger ground going back to the panel
  • any junction box with metal conduit going back to the panel
  • A split-bolt clamp onto the Grounding Electrode Conductor (bare wire between service panel and ground rods/Ufer/water main).
  • Do not run to any random water or gas pipe.

A ground wire is needed because it conducts electricity well, and that is needed to "clear a bolted fault" (trip the breaker on a short circuit). For instance if your pump had a dead short to frame, well over 200A would be able to flow. A ground wire allows that to happen, resulting in breaker trip. A ground rod would only let maybe 5 amps through, which would not trip the breaker, and would energize the chassis of the pump and ground nearby.

Mind you, that's traditional thinking. The GFCI complicates it a bit, because you don't need 200A to flow to instant-trip a GFCI - 6 milli amps will suffice. And a ground rod would let that much through. As such, that type of thing is allowed in European installations which have "whole-house GFCI" (RCD), which are quite common in Europe. The downside of RCD is 6mA is too sensitive for a whole house, so they de-tune it to 30mA, which makes it less able to protect human safety.

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