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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: breaker box

and wiring description: 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 open socket close up of the back

Edit 2: full electrical panel and back of receptacle full panel back of receptacle

Wire Gauge:

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FreeMan
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5E4ME
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    What's going to determine if you can simply swap outlets or if you actually need to upgrade the whole circuit is going to be the size of the wire. See if you can see any markings on the cable jacket that indicate what size it is. Or, if you can't find anything, with the power turned off, you can use a wire gauge to check (example: https://www.amazon.com/SE-JT47WG-C-Dual-Sided-Non-Ferrous-American/dp/B00VRRIVX8/) – Nate S. Feb 10 '21 at 17:23
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    Also, since you're renovating anyway, is the current circuit 3-wire or 4-wire? If it's an old 3-wire, it would be a good idea to take this opportunity to retrofit a ground wire. – Nate S. Feb 10 '21 at 17:25
  • @Nate S. Combine your two comments and copy into an answer form. – Jim Stewart Feb 10 '21 at 17:26
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    @JimStewart, it's not an answer yet; it's asking clarifying questions. Once OP provides that info I will. – Nate S. Feb 10 '21 at 17:26
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    Just a clarification, NEMA does not designate a 40A receptacle, the odd code specified receptacle for a 40A breaker is a 50A receptacle (NEMA 10-50 or 14-50). The cord is spec'd 40A due to wire size. Please do update wire size connected to breaker, but really it is unlikely that somebody ran wire smaller than size capable of 40A for a 240V range. – NoSparksPlease Feb 10 '21 at 18:10
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    We need to know the size, metal (copper vs aluminum) and insulation type of the existing wires, so we can assure the wire is ready for 40A. We also need to know if there's a metal conduit, metal jacket on the wire, or ground wire. – Harper - Reinstate Monica Feb 10 '21 at 19:36
  • I added some pictures of the wiring. It looks like bare braided ~14 gauge metal on the neutral and rubber-jacketed braided ~12 gauge on the two hots. I was expecting to find copper wire but since it's silver I guess it's aluminum? – 5E4ME Feb 10 '21 at 23:54
  • @5E4ME -- can you post photos that show the label on the inside cover of your panel *in full*, as well as the back of the range receptacle box? – ThreePhaseEel Feb 11 '21 at 00:03
  • @ThreePhaseEel pics added – 5E4ME Feb 11 '21 at 00:21
  • @5E4ME -- can you get us a shot of the inside of the box that shows where the cable enters the box clearly? – ThreePhaseEel Feb 11 '21 at 00:53
  • @ThreePhaseEel apologies, here you go http://imgur.com/a/uvk9KMP – 5E4ME Feb 11 '21 at 01:00
  • @5E4ME -- can you get us the overall diameter of the bare wire? – ThreePhaseEel Feb 11 '21 at 01:19
  • @ThreePhaseEel looks like 4AWG overall for both types of wire comprised of individual 14AWG strands. http://imgur.com/a/i1D6KhG – 5E4ME Feb 11 '21 at 01:33
  • @Harper - Reinstate Monica is this cable allowed for an electric range (or a dryer!) requiring a neutral? I am pretty sure my dryer cable (1970 house) has three equally insulated conductors (but no bare conductor for a ground) so it is grandfathered. What would a cable with 2 insulated + 1 bare be used for? Some electric welders? Certain cooktops which only need 240 V? Some electric vehicle charging stations? – Jim Stewart Feb 11 '21 at 03:03
  • This GE panel (states 32 poles maximum, 200 A service) appears to be a split bus. My panel is that same type only slightly smaller at 26 poles maximum, 150 A service. The pencil listing of breakers in this poster's panel appears to conflict with the wiring diagram. – Jim Stewart Feb 11 '21 at 03:34

5 Answers5

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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.

ThreePhaseEel
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    It is aluminum wire and OP also needs to be careful about making those connections on the new outlet. They will need to ensure the 10-50R outlet is rated for #4AWG aluminum and they will need to refresh the anti-ox paste and torque the lugs correctly. Workmanship is very much more important when fitting aluminum. – J... Feb 11 '21 at 14:39
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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.

Jim Stewart
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    The OP's install falls under the "grandfathering" clause in the Exception to NEC 250.140, and they also could retrofit a grounding wire to this setup if they wanted to move to 4-wire, especially if this cable is 4-4-4 instead of 6-6-6 – ThreePhaseEel Feb 11 '21 at 02:05
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    Thanks for the help, everyone. It sounds like I just need to bite the bullet and have a professional upgrade this to a 4 prong setup. A couple more days of microwaving food is a small price to pay for having a safe range :) – 5E4ME Feb 11 '21 at 02:14
  • I am not an expert. Get confirmation from one of the experts. If the uninsulated strands are inside the outer sheath it may be that in the past this could be used as a neutral and so could be grandfathered in. You need one or more of the experts to comment or answer. Maybe the original range for this house only needed 240 V. But AFIK all modern ranges with an oven as well as surface burners, require 120 V and 240 V. – Jim Stewart Feb 11 '21 at 02:31
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    If the cable for the range is wrong (and this has yet to be confirmed), then one must suspect the wiring for the electric dryer. Modern wiring for electric dryers is 4-wire just like wiring for a range. If the OP has an electrician in for the range he should have the dryer wiring upgraded to 4-wire at the same time, if his dryer requires that. In our 1970 house, the range was the was 4-wire, but the dryer 3-wire. I have yet to rectify the dryer situation, but I intend to retrofit a ground and change to a 4-wire cord – Jim Stewart Feb 11 '21 at 03:11
  • See https://www.thespruce.com/wire-a-4-prong-dryer-outlet-1152236. – Jim Stewart Feb 11 '21 at 03:40
  • @JimStewart Condition (3) of the exception to NEC 250.140 that allows grounding via the grounded conductor includes "the grounded conductor is uninsulated and part of a Type SE service-entrance cable". – NoSparksPlease Feb 11 '21 at 04:42
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    This answer misses the key points about how range plugs have changed over the years and why and it misses the clear and unambiguous options OP has to deal with it. – J... Feb 11 '21 at 14:34
  • I am possibly missing something. This cable is missing an insulated conductor needed for NEUTRAL. The old practice for dryers was to use a 3-wire cable which had 3 wires identically insulated and so was missing a ground. On the dryer connection block the chassis gnd was bonded to the neutral. The new practice is to use a 3 + gnd cable, new receptacle, new cord, and no bond on dryer connection block. – Jim Stewart Feb 11 '21 at 15:42
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    @JimStewart, what you're missing is that this type SE cable has an uninsulated *neutral* and *no ground*. It's probably the only type of cable that does not insulate the neutral, but it is designated for use as a neutral by code nonetheless. – Nate S. Feb 11 '21 at 17:44
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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.

Harper - Reinstate Monica
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  • I don't think you can run the SE at 75C here -- as of the 2008 NEC, when it's indoors used as a branch circuit or feeder, rather than as a service conductor, it's limited to 60C. There's a discussion of that here: https://forums.mikeholt.com/threads/ser-cable-temperature-rating.47880/ – Nate S. Feb 11 '21 at 17:16
  • Wait, after researching it a little more, apparently that section changed again in 2014, 2017, and 2020 code updates, so the exact rules will depend on what OP's jurisdiction has adopted. Possibly, depending on the year that applies, whether the walls it runs through are insulated will make a difference. If it's 2017 or 2020, most likely the 75C rating can be used, so I was (mostly) wrong. – Nate S. Feb 11 '21 at 17:28
  • What are the proper uses of SE cable? – Jim Stewart Feb 11 '21 at 17:34
  • @JimStewart, SE stands for Service Entrance -- it's the type of cable a utility would use for their service drop. Most of the other uses for it are no longer a good idea, now that grounding is a requirement. – Nate S. Feb 11 '21 at 17:36
  • Oh also, you may be right that a 30A that could accept that wire would be hard to find, but OP needs to upgrade to a 14-50r, and those pretty much always accept #4 Al (often at 75C). For example, this Leviton would work: https://www.amazon.com/Leviton-279-S00-Receptacle-Industrial-Grounding/dp/B01M9FC5AR/ – Nate S. Feb 11 '21 at 17:38
  • @JimStewart The designed purpose of SE is for service entrance, but NEC 338.10(B) specifies how it is allowed to be used as a branch circuit cable, and specifically pertinent to this discussion 338.10(B)(2) Exception allows the uninsulated conductor to be used as a neutral in accordance with the appliance grounding requirement in 250.140. – NoSparksPlease Feb 11 '21 at 18:01
  • @NoSparksPlease so SE was at one time a code allowed allowed cable for this use? It would then be grandfathered and one could just retrofit a ground (along a different path) to install the range with a full 4-wire? This cheapest approach of course neglects that Harper observes that a hole was made in the box with stone implements. I knew it! Finally evidence of the long suspected Clovis remnants. Now that we know they are here it cannot be long before we find their villages in remote canyons in W Texas or New Mexico. – Jim Stewart Feb 11 '21 at 19:09
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    @JimStewart Yes, sometime in the early 90s the 3-wire connections were outlawed. Til then, you COULD use SE cable since the bare wire was neutral. You could also use /3NM without ground (white neutral) which is what you have, but that was nonexistent once the old stock ran out. Lots of people just switched to using /2NM w/gnd, but that was never legal. /2 w/g NM's ground wire is NOT allowed to be neutral. – Harper - Reinstate Monica Feb 11 '21 at 19:53
  • @JimStewart I don't think adding a ground would be technically acceptable. 338.10 says the when SE is used for branch circuits the uninsulated neutral conductor can only be used as a ground except when you have an existing circuit where you are 250.140 exception grounding via the grounded conductor. No provision is made in the exception to allow the uninsulated conductor to be used as a neutral when adding a ground compliant with 250.130(C). Adding a ground may actually be better, but it doesn't appear a code proposal to do that has been made or accepted. – NoSparksPlease Feb 11 '21 at 20:05
  • @NoSparksPlease It should be allowed in the general rules for retrofitting grounds, which are pretty broad. I can't recall anything that said "Can't retrofit grounds for cable types X Y or Z". – Harper - Reinstate Monica Feb 11 '21 at 20:13
  • @Harper-ReinstateMonica Wouldn't you have to consult the permitted uses for the cable type in question? – NoSparksPlease Feb 11 '21 at 21:01
  • @NoSparksPlease -- interestingly enough, 338.10 cites the whole of 250.140 instead of citing *only* the Exception to the latter section of Code... – ThreePhaseEel Feb 11 '21 at 23:48
  • @Harper-ReinstateMonica -- note that while the cable's capable of 75degC operation most likely, their panel's too old for 75degC ratings to be used, sadly :/ – ThreePhaseEel Feb 11 '21 at 23:48
  • @ThreePhaseEel In 338.10 wouldn't "in accordance with" mean you could use an uninsulated neutral where 250.140 allows an uninsulated neutral, which is only in the exception? – NoSparksPlease Feb 12 '21 at 00:33
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    @NoSparksPlease -- that's a reasonable interpretation, at least. TBF: old SE-cable range runs like the OPs don't really have a particularly good upgrade path short of lobbing a transformer-and-subpanel setup or a brand-new cable run at the problem – ThreePhaseEel Feb 12 '21 at 00:37
  • That looks like the original appliance didn't want a neutral. That particular outlet has been abused to make 240v only outlets quite a bit. – Joshua Jul 13 '22 at 11:02
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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.

NoSparksPlease
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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.

GdD
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