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In the picture is the NEMA 10-30 I want to change for the safer grounded 14-30. I learned of the danger of this old receptacle here As you can see in the picture there's a ground that I can use to put to upgrade to the NEMA 14-30 receptacle.

I was apprehensive about using the dinky little ground attached to the 15 amp receptacle but I texted an electrician I knew and he said it's a non current carrying conductor and should be okay. I also asked the HVAC guy that was installing my AC and he said that sounds about right as well, and should be good enough.

I'm still a little worried so here I am asking the rest of you, just to triple check.

Update: Sorry for the delay. So I bought 10awg solid copper wire and screwed into the back of the metal box.

I confirmed that there’s metal conduit leading to the box. I put a wire nut that was good for 3 10awg wires. There are two being inserted along with a 12/14awg wire. I twisted the shit out of the nut and ran a 10 awg wire to the new NEMA 14-30 receptacle. I have yet to power it on.

Here’s a pic enter image description here

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    Start with (breakers off) removing both receptacles and pulling them aside and taking another picture so we can see all the wiring in the box.
    – Ecnerwal
    Commented Jun 9 at 2:01
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    @Ecnerwal Updating.
    – Biclops
    Commented Jun 9 at 3:38
  • As you can see there's only the dinky little ground that came from the other outlet. I was hoping there'd be a big one attached to the case.
    – Biclops
    Commented Jun 9 at 3:44
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    Looks like maybe the dryer and receptacle are fed by a conduit, the conduit itself may provide a good ground for the dryer, the gray cable sends power to another outlet, and the ground wires for the outlet and cable are done incorrectly. If so you could ground the dryer and the the grounding to the receptacles. Ask how.
    – jay613
    Commented Jun 9 at 4:09
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    The "dinky little ground" goes onwards from the other outlet. Ground to this box is via the conduit feeding both outlets. This is why we need to see pictures, because we can see things you don't know are there.
    – Ecnerwal
    Commented Jun 9 at 11:28

3 Answers 3

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Just a hunch, so this may get disproven...

Conduit to the rescue!

While the upper right wires going to the 15A duplex receptacle appear to be a cable (though the coloring looks strange), the lower right wires going to the 15A duplex receptacle and the wires going to the 10-30 receptacle are all going down into one location. That looks like metal conduit.

In addition, the two hot wires to the 10-30 receptacle appear to be black. Typically (but not 100% guaranteed), wires in a cable with be black, red and white (with white used for neutral if neutral is needed, as is the case here). That also points to individual wires in conduit.

In addition, there is no ground going down the presumed conduit. Which makes me think:

  • If this is metal conduit and installed properly, that provides a suitable ground path. Done.
  • If this is not metal conduit, or not entirely metal conduit (e.g., transitions somewhere to PVC or other conduit types) then it does not provide a ground path. However, then a ground wire (10 AWG for a 30A circuit) can be added inside the conduit.

Note that metal boxes are used as part of the grounding system whether or not you use metal conduit. So:

  • Incoming power always grounds to the box first. Meaning if you do have to add a ground wire, connect it with a grounding screw to the box.
  • Most better quality 15A and 20A receptacles (and all switches) automatically get ground from the metal yoke touching the metal box. So no ground wire needed for the 15A receptacle. Or at least, once you replace the 10-30 with a 14-30 and replace the junky old 15A with a nice new better quality one, preferable with screw-to-clamp connections.
  • The cable to the other receptacles should have its ground wire attached to the box, not to the receptacle in this box. That is important because if the receptacle is wired up but pulled out from the box (e.g., as in these pictures), ground is not actually connected to the cable. Which means in the unlikely (but possible) situation of leaving this stuff "hanging out" and turning the breaker back on so the other receptacle works, the ground on the other receptacle would be floating and not provide any safety.
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    The box needs a threaded ground hole tapped or one of those conduit nuts with a terminal, and I don't think there are self-grounding 14-30 receptacles. It needs some work but I think this is the right approach.
    – jay613
    Commented Jun 9 at 4:22
  • Lesson learned, do not leave powered receptacle hangin out of the wall.
    – Traveler
    Commented Jun 9 at 4:51
  • Hmmm so you're telling me I'm supposed to attach the ground to the box? That makes sense because I plugged in a GFCI outlet tester and it said open ground when I pulled out all the receptacles but when I pushed everything back in, it said it was correct. How would I attach the ground to the box if there's no screw? Would I have to tap my own hole and screw down the ground?
    – Biclops
    Commented Jun 9 at 5:29
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    Given the wire colors to the dryer (two blacks and a white, and then the black and white to the outlet) it's a pretty good bet there is conduit here. A self-threading ground screw and you're set. The gray cable is presumably going elsewhere (perhaps an outside outlet, given that gray jacket is typically UF-B.) There might be one hole smaller than the others, with threads, (without the newer "bump") but if not, self-threading gets the job done.
    – Ecnerwal
    Commented Jun 9 at 11:20
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    Looks OK to me.
    – manassehkatz-Moving 2 Codidact
    Commented Jun 28 at 2:00
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Officially, no, that is not legal under the NEC. You can retrofit ground for ungrounded circuits that were legally installed, but the target ground wire must be large enough for the previously-ungrounded circuit. Assuming the 15A circuit is wired with a 14Ga or 12Ga ground, that is not allowed for a 30A circuit.

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    Because they just didn't know the rules. A ground wire performs multiple functions. But for the key one of dealing with certain types of short circuits, an undersized ground wire would be a high-resistance connection that could, under certain circumstances, result in a short circuit not tripping the breaker as fast as desired.
    – manassehkatz-Moving 2 Codidact
    Commented Jun 9 at 4:42
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    @biclops the guy told you that because it's better than the old outlet. However a bolted fault (hot-ground short) could result in that #14 ground glowing cherry red for a short time before the breaker trips. That's why code wants a #10.
    – Harper - Reinstate Monica
    Commented Jun 9 at 18:38
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    @Biclops See diy.stackexchange.com/a/74996/18078 and the page linked from it. Properly assembled metallic conduit is an acceptable grounding path. Or you can choose to use the conduit to pull a #10 copper ground wire, if you prefer. Code accepts either. Steel is less conductive than copper, but conduit makes up for that by there being more of it. There should be a 10AWG wire from the receptacle to the grounding screw in the box.
    – Ecnerwal
    Commented Jun 9 at 19:54
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    If you install the grounding wire in the conduit, it should connect first to the box, then a pigtail (of the correct size for the respective receptacle circuit's amperage) should connect from the box screw to each receptacle. If you don't install the grounding wire, the pigtails should still connect to each receptacle (though the 120V one MAY be optional) from the box screw. That's why you need to add the box grounding screw.
    – Ecnerwal
    Commented Jun 9 at 22:36
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    @Harper-ReinstateMonica: Could a GFCI or GFCE on the higher-current circuit reduce the required ground lead current carrying capacity for the ground lead? A fault current low enough not to trip the detector wouldn't measurably heat even a 22ga grounding lead, and a fault current sufficient to trip the detector should cause a current trip within a dozen milliseconds.
    – supercat
    Commented Jun 10 at 15:05
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NEC 250.130(C) is the retrofit ground rule.

It says you must use a #10 ground. However, you can go to any number of places:

  • The Grounding Electrode Conductor, that large bare wire from the panel to the ground rods or water pipe, and any other wires bonding something to that GEC
  • Any junction box with a #10 or larger wire back to the panel
  • The panel the circuit comes from
  • The main panel
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  • Thank you for the response, so a #10 wire is adequate for a NEMA 14-30? I’m a diy’er and I was worried it was too small.
    – Biclops
    Commented Jun 10 at 18:23
  • @biclops yes, #10 ground covers any circuit from 21 to 60 amps. Under normal conditions. And ground retrofits are no exception.
    – Harper - Reinstate Monica
    Commented Jun 11 at 18:05

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