Is it safe to swap a 30A "Dryer Socket" with a 40A "Range Socket" if the breaker is 40A?

Question

Just bought a house built in 1979 and am working on renovations. Today we had a new range delivered and ran into an issue trying to install it. Essentially, the old range was connected to a 30A "dryer socket" in the kitchen while the new one requires a 40A "range socket". The delivery guys were adamant that all we had to do was pop over to a store and swap out the receptacle in order to get it working.

Based on Dryer Outlet in the kitchen?, I'm skeptical that it will be so simple. Checking the breaker box:

and wiring description:

shows that the old circuit has a 40A breaker. Given that, is it ok to assume that the wiring for this circuit is also safe up to 40A and I truly can just swap the receptacles and call it a day?

30 amp dryer plug is hooked to a 40 amp double breaker, is this ok? indicates that the current setup maybe shouldn't have existed in the first place so I'm trying to be cautious about how I fix this.

Edit: here are some pictures of the wiring

Edit 2: full electrical panel and back of receptacle

Wire Gauge:

Answer 1

It appears to me that this cable has two insulated conductors for the two hot legs plus an uninsulated conductor to be used as a ground, i.e., it does not have a third insulated cable to be used as a neutral. The cable is wired to the receptacle using the uninsulated conductor as a neutral. This is not allowed by code.

This cable can legally supply 240 V, not both 120 V and 240 V. It is not suitable for any appliance which requires both 120 and 240 V. What are the requirements of your new range?

Unless your new range is a special design which requires only 240 V, you must replace this cable all the way back to the panel or subpanel if there is one. Look at the installation instructions for the range. It should tell you whether it requires a neutral. If it does, then you will need a new (4 wire) cable.

You could use a 3-wire appliance cord and plug it into this receptacle and the range would work perfectly, but if the range requires a neutral, then current will regularly be flowing in the uninsulated conductor. This is not allowed by code.

If the cable had 3 inslated conductors, you could use it as is or you could retrofit a ground, but you cannot retrofit a neutral.

Answer 2

Go for it, for now at least...

You appear to have at least 6AWG if not 4AWG aluminum present there, so you will have no trouble with a full-sized range circuit using the existing 40A breaker and a NEMA 10-50R receptacle. Since this is aluminum wire, though, you'll need a Cu/Al rated receptacle, and also to make sure you use anti-oxidant grease on the connection and a torque screwdriver to accurately tighten the lug screws to the specification torque.

You'll want to find a way to run a separate grounding wire back to the panel or the grounding electrode system in the future, though

In the future, though, you'll want to run a 10AWG copper wire from this box back to the panel, or any other point on the existing grounding electrode system, so that you can replace this (hazardous) NEMA 10 with a (much safer) NEMA 14 receptacle and convert your range over to the matching 4-wire (NEMA 14) plug.

Answer 3

You are asking is it safe: Installing a NEMA 10-50 range socket. No, that is not safe. This was banned in 1996 because of the body count. The fact that yours was installed prior to 1996, and is thus "grandfathered", does not make it any safer.

When your installers say "it's safe", they mean "it's safe FOR THEM" because they won't be using your range. Also, appliance installers don't have an electrician's license at risk.

If your range does not require neutral, then it should be using a NEMA 6-50 plug. If the range does need neutral, then you are safer with a NEMA 14-50 type plug, and that would mean retrofitting ground to this socket. The ground must be #8 (for reasons) either back to the panel or back to a box which has #8 back to the panel, or has non-flexy metal conduit back to the panel.

Also, this is a goobed up mess.

The #2 problem is that a junction box can't just have a hole bashed in it by smashing a rock against it. The cable entering it needs to have a proper cable clamp, which means the box needs a proper knockout.

The cable is #4 SE cable, and that cable can do 2 interesting things: First, that bare wire actually does get to be a neutral wire. (or a ground, your choice). And second, it's good for 55A generally, but since it can run at 75 degrees C, we can actually get 65A out of this wire (but not going into that old 60°C panel; we'd have to pigtail to larger wire outside the panel).

Aluminum is fine at these large sizes, but only if the receptacle is rated to attach to aluminum wire! (remember; that's what caused all the trouble in the 1970s!) What's more, I would be very surprised if a 30A receptacle was rated for #4 wire, since it only needs #10 copper (or #8 aluminum if it accepted aluminum). So I am suspicious as to how the wires were attached to the NEMA 10-30 recep.

The size is #4. The size of the individual wire strands is irrelevant, as you cannot use the wires individually. At all. The only purpose of stranding is to increase the flexibility of the entire wire. You must not remove some strands to get a wire to fit a too-small connector.

If the receptacle is not rated for aluminum, or not rated for #4 wire, replace it with one that is. That shouldn't be hard with NEMA connectors.

Answer 4

That cable appears to be type SE cable, and so it would be allowed by the exception to NEC 250.140 to replace the 30A receptacle with a 3-wire NEMA 10-50R. Below is the code section you can read. It seems to me your existing installation fits the conditions, even condition (3) about the uninsulated cable.

It would be better to upgrade to a 4-wire, but not required.

Reading the section below can be confusing, understanding of Code terminology is critical. "Grounded Circuit Conductor" is what is commonly called the neutral, and the "Equipment Grounding Conductor" is the ground.

250.140 Frames of Ranges and Clothes Dryers. Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be connected to the equipment grounding conductor in the manner specified by 250.134 or 250.138.

Exception: For existing branch-circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be permitted to be connected to the grounded circuit conductor if all the following conditions are met. (1) The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120-volt derived from a 3-phase, 4-wire, wye-connected system. (2) The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum. (3) The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment. (4) Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.

Answer 5

You are right to be skeptical. The components in your circuit are the breaker, the outlet, and the wiring in between, which is the unknown in this case. If the wire is the right gauge (8 I think), it's condition is good and has been run correctly you could change the outlet, if it's too small a gauge you could overload the wiring.