Converting NEMA 10-30 to 14-30 using ground from adjacent 15 amp receptacle

Question

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

Answer 1

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.

Answer 2

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.

Answer 3

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