Outlet looks like a NEMA 10-50 but is only stamped at 30

Question

There is an electric stove plugged into this outlet. I can't tell what plug it is to make an adapter for car charging.

This is in the U.S.

Answer 1

It looks like a NEMA 10-50 all right, but it is labeled 30A.

Electrical Code 110.3 requires you obey labeling and instructions on every device. Therefore, this mismarked device can only be breakered 30A, but anything you'd plug into it will pop a 30A breaker. It is useless and must be taken out of service and tossed. It may not even be a Proper NEMA connector, so a 10-50P may not even fit. Not that you should be using a NEMA 10 to charge an electric car! It invites a shocking situation.

The problem with NEMA 10

Even if you refit a NEMA connector, these large connectors are not intended for frequent plug/unplug. They will quickly take damage and terminals will start to break. That's where NEMA 10 becomes a super bad problem. They don't have a ground pin. They are illegal for new work, but due to lobbying by the appliance industry, they are allowed to continue in service in older homes. They "made it legal" to bootleg ground on ranges and dryers.

The problem is if anything goes wrong with the neutral connection, the chassis of the machine will become electrified. This has killed, and it's typically reported as a "miswired" dryer or range receptacle, however the receptacle was correctly wired. It simply failed, which is a normal and common occurrence and it shouldn't fail deadly: it shouldn't electrify the chassis of machines. But it does, and that's what makes NEMA 10 dangerous.

Size up what you've got

Pop the socket cover off the wall and take a look inside. You want to know the size of the wires, and if they are aluminum, how many there are, and what colors.

• First account for the hot wires. There must be 2, either black or red. Two blacks is OK.
• Next, account for neutral. If a white wire is present, that is neutral. It might be bare if it's the only remaining wire. Sometimes it is a web of bare strands wrapped around the hots.
• last, ground. If neutral is accounted for, and there's still an unaccounted for bare, green or green/yellow wire, that is ground. If both neutral and ground are present, that is awesome. However ground can be retrofitted by installing a single wire -- neutral cannot.

Now look at the size of the wires, and we are concerned with the "hot" wires only. They will be either 10 AWG, 8 AWG, 6 AWG, or possibly 4 AWG. (Getting larger as the number lowers). This will be marked on the individual wires maybe, the cable sheath surely, or the diameter of the wires can be measured and look it up on the Internet.

Also determine if the wires are aluminum. If they are aluminum, add 2 to the effective AWG. So #6Al performs like #8Cu. Assuming copper:

• if the hots are 10 AWG you must breaker for 30A and you must use 30A receptacles (not that one).
• if the hots are 8 AWG you must breaker for 40A and use 50A receptacles (really).
• if the hots are 6 AWG you must breaker for 50A and use 50A receptacles.

Adapt what you can

Now most likely, your car charger requires ground (uses a NEMA 6 hot-hot-ground or 14 hot-hot-neutral-ground). And most likely, your stove requires neutral (uses NEMA 14 or 10 hot-hot-neutral). Neutral is not ground, no matter what you've been told.

But if you don't have ground, you can retrofit ground, simply by getting bare #10 wire and routing it via any possible means from the socket to the main panel, or any grounded part of your electrical system where the ground wire is #10 or larger, or any non-flexible metal conduit that goes all the way back to the panel, or anywhere on the grounding electrode system (the bare wires grounding the panel to water pipes or ground rods). You cannot use random water pipes for grounding, with some exceptions.

The only receptacle which can satisfy both needs is NEMA 14, which happily also fixes the dangerous NEMA 10 situation. Also happily, any range is designed to accept either a NEMA 10 or 14 cord, and can be switched just by changing the cord and removing the bootleg-ground jumper.

Your car charger is probably wired NEMA 6 (hot-hot-ground), but it is perfectly legal to plug it into NEMA 14 with an adapter, extension cord with NEMA 6 and 14 on opposite ends, or just change the cord on the charger.

If your circuit is 30A, you can also have more than one receptacle on it. So a 30A circuit could be extended to a new receptacle in the garage. That is a no-no with 40 or 50 amp range/oven circuit.

Answer 2

That is clearly a 5, not a 3 before the 0. It’s not mismarked. Use a standard NEMA 10-50R.

I just filtered and brightened and sharpened and zoomed your picture. Even without all that if you look closely you'll see that the dirt and fuzz makes it look like a 3. 5s usually have a flat top and 3s a curved one.