I've read various posts here about the advantages of 4-prong over 3-prong, such as the dryer cabinet can become hot if there is an interrupt in the 3-prong neutral/ground. Examples:

Dryer Outlet - 4 prong to 3 prong

Converting a Samsung Dryer from a 4-prong cord to a 3-prong cord?

In the our utility closet/room of our house, I will be moving our 3-prong dryer receptacle that is on a non-GFCI 30amp breaker. It supplies our 2007-ish 3 prong problem-free dryer. Printed installation instructions: "Materials you will need ... dryer power cord kit (not provided with dryer) UL rated 120/240V, 30A with 3 or 4 prongs. Identify the plug type as per the house receptacle before purchasing line cord". It also contains: "NOTE: Since January 1, 1996, The National Electric Code requires that new construction utilize a 4 wire connection to an electric dryer." And it gives details for 3 wire and 4 wire connections with specifics on the OEM ground strap. It also says that a 4 wire connection "must be used for mobile home installation", which is not our situation.

Relocation plans are to use a junction box at the current location, then run 4-12 feet (depending on route) to a reinstall of the old receptacle. What are the minimum code requirements in terms of 3-prong versus 4-prong?

Specifically, can I just extend as described, or ... does code require the entire circuit be redone to 4-prong? or does it require the just the new work to be 4-prong?

  • "prep it for a not-in-the-foreseeable future 4-prong dryer and tag the unused wire as such" There are three issues with switching: receptacle, cord, ground wire. If you are prepping it for the future then you are taking care of the ground wire - which is the only potentially complicated part. So you might as well make the other 2 changes at the same done and be done with it. Commented May 31, 2018 at 17:59
  • @April -- is that tube the wires are coming out of in your 1st photo made of metal or plastic? Can you pull on the wires there with the power to the circuit turned off and have slack start coming out? Commented May 31, 2018 at 19:07
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    Then what is that I see in the bottom left corner of the hole in the photo? Commented May 31, 2018 at 21:43
  • @ThreePhaseEel I saw that in the corner too. Sure looks like some sort of conduit. Commented May 31, 2018 at 21:58
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    @ThreePhaseEel sounds like only three options (1) use any routing desired to run #10 ground back to the panel. (2) swap in a GFCI breaker plus disconnect the bootleg in the dryer. Either way, code requires the receptacle to be 4-prong NEMA 14 and hence a new cord. Or (3) replace the 3-prong cord with a longer 3-prong cord, leaving the house wiring as is.
    – April
    Commented May 31, 2018 at 23:41

4 Answers 4


Since the 1999 NEC, if you modify this branch circuit to extend it then you need to upgrade it to a properly grounded NEMA 14-30 outlet or it will not meet code. Most AHJ require an electrical permit to wire this extension and what you propose will not pass inspection.

From 2011 NEC below with my emphasis. Note that "grounded circuit conductor" is NEC-speak for the white neutral wire in your existing installation.

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.

Note that the grounding wire can be a retrofit and it doesn't have to be a home run back to the service panel. For example if you have a common grounded 110V outlet (NEMA 5-15R) nearby you can bond to this ground if the branch circuit goes back to the same service panel.

Here's a snippet of NEC that talks about retrofit grounds:

250.130(C)(1) A non-grounding type receptacle can be replaced with a grounding-type receptacle if an equipment grounding conductor is installed and connected to any accessible point on the grounding electrode system.

250.130(C)(2) A non-grounding type receptacle can be replaced with a grounding-type receptacle if an equipment grounding conductor is installed and connected to any accessible point on the grounding electrode conductor.

250.130(C)(3) A non-grounding type receptacle can be replaced with a grounding-type receptacle if an equipment grounding conductor is installed and connected to the equipment ground terminal bar within the enclosure where the branch circuit originates.

250.130(C)(4) A non-grounding type receptacle can be replaced with a grounding-type receptacle if an equipment grounding conductor is installed and connected to an equipment grounding conductor that is part of another branch circuit originating in the same enclosure.

  • I believe that is correct. The only part I’m uncertain about is the wire gauge required. Whether 14 AWG is sufficient. I could look it up later. Hopefully one of the more active electricians will chime in.
    – Stanwood
    Commented May 31, 2018 at 21:52
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    Indeed it must be #10. But it only needs to reach any part of your equipment safety ground network which has #10 or thicker path back to the panel, OR, any part of the grounding electrode wires going to ground rods, ufer, water pipe clamp etc. Commented May 31, 2018 at 22:13
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    @April I almost added to that "You can't just use a water pipe" ... but I'm not....entirely....sure and it boils down to hairsplitting interpretations of 250.130(C)(1). Also, you can't validate piping you can't see, and if a plumber alters your piping with PVC or Pex, or the water company fits a plastic meter, they could inadvertently sever the ground. It's not his job to assure electrical continuity of pipes on the off chance someone is randomly using it as a ground. Commented May 31, 2018 at 22:39
  • Is there a water heater, baseboard heater, or cooking appliances nearby? They may have a thick enough ground wire.
    – Stanwood
    Commented May 31, 2018 at 22:41
  • @April what I mean is the retrofit ground has to be installed at the old location just long enough for you to officially declare it to be a retrofit at that location. Once you have characterized it as a retrofit ground at the original location, you should then be able to extend off it. Commented Jun 2, 2018 at 6:20

There are others (Harper, ThreePhaseEel) who will likely provide a ton of details. But in a nutshell:

  • 3-prong does not provide the same level of safety as 4-prong.
  • 3-prong is grandfathered in, but when you make a change you should switch to 4-prong. New work should definitely be 4-prong NEMA 14-30. I don't know if code strictly requires a change to 14-30 in your situation (the real pros can weigh in on that). But from a practical standpoint, once you are already doing the work you might as well spend a few $ on a new receptacle and new power cord and do it right (unlike my electrician years ago).
  • When you switch, in addition to the new 4-prong receptacle and new 4-prong dryer cord to match it, there is a ground-neutral bonding jumper that MUST be removed on the dryer.

Your pictures pretty clearly show that there is no existing ground, and you have also made it clear that a new cable back to the main panel would be quite expensive. If a retrofit ground using existing wiring (e.g., connecting to the ground of the washer receptacle, provided it is legal (large enough wire or other grounding mechanism)) is not practical then I would consider a combination of (a) replacing the regular breaker with a GFCI breaker to provide protection and (b) replace the existing 3-prong dryer cord with a longer 3-prong dryer cord to take care of the extra several feet. I do NOT recommend using an extension cord - they are available but that is not a good idea, and may even be against code for a nominally permanent installation.

  • The ironic thing is: I just checked my own dryer, which was moved a few feet (in order to vent properly - the original owner had been venting inside!) by a "professional" years ago - and it was never changed from 3 to 4. I just added that to my To Do List. Commented May 31, 2018 at 17:18
  • I don't know when it was codified. That isn't really the issue. The issue is what is the safe/"right" thing to do today. For any new install or move, it should be 4-prong. In my case, I'm not doing a new install or a move but I will, for safety's sake, change it anyway. The parts cost is minimal. In my case, the panel is right next to the dryer, so even if I have to run a new ground wire it is no big deal - I just never looked before and when I moved my dryer years ago I didn't know enough about electricity to do it myself (or to know what wasn't done right). Commented May 31, 2018 at 17:38
  • From 2014: "It wasn’t until 1996 when the National Electrical Code (NEC) was updated to require 4-prong dryer outlets in all new homes. Existing homes may still use 3-prong outlets, as the NEC changes are limited strictly to new homes." fredsappliance.com/service/…
    – April
    Commented May 31, 2018 at 17:55
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    I edited option 2 to require a conversion to NEMA 14. The problem is a NEMA 10 plug requires a bootleg strap connecting chassis to neutral, and that won't play well with a GFCI solution. Commented May 31, 2018 at 23:02
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    If I understand you correctly, that would make chassis ground go (by itself) to the grounding terminal on the new NEMA 14 receptacle, and from there it would go nowhere. So the protection is provided because if some current is going to the chassis due to a short then there is not enough coming back on neutral, and GFCI trips. As opposed to if the jumper is still in place with NEMA 10 because then any contact by a person to the chassis (=ground=neutral) might potentially affect things ever so slightly (though not normally enough to be dangerous) and cause a nuisance trip of the GFCI. Right? Commented May 31, 2018 at 23:07

Your options here

You have several options here for making this safer and Code-compliant:

  1. Rerun the circuit with a grounded cable (awkward, I know, but probably not impossible). This way, you could also put in a proper box and flushmount receptacle (surfacemount type NEMA 14s exist, but they are annoying compared to the box-mounted counterparts)
  2. Switch the receptacle for a NEMA 14, swap the breaker for a 30A two-pole GFCI (may not be possible if the breaker's a quadruplex/half-width type), and put the requisite "No Equipment Ground" and "GFCI Protected" labels on it, as per 406.4(D)(2)(c).
  3. Retrofit a 10AWG ground wire back to a suitable grounding point in the electrical system (note: not a water pipe), as per 250.130(C). You'll also get to upgrade the receptacle to a NEMA 14 this way.

Given that option 1 is going to be a pain in the arse for you, and option 3 an equal pain in the arse, I'd recommend option 2, although you'll need to patch a junction box in where the existing surface mount receptacle was located in order to extend the wires to the new location if you do that. You'll also want to make sure you can fit a 30A, 2-pole GFCI breaker into your panel before you start shopping for parts for that.

With all of these three options, you'll be fitting a 4-wire cord to the dryer and pulling the bonding jumper from it.

  • Option 2 only works if you stay at the old location. A new location is new work, and absolutely requires a proper ground. Commented Jun 1, 2018 at 16:32
  • @April Option 2 requires fitting a NEMA 14 plug. Since NEC 110.3 requires you to install that according to the appliance's instructions, part of that will be disconnecting the chassis-to-neutral wire, yes. Commented Jun 1, 2018 at 16:58

I see 2 options.

  1. Run a totally new cable from the panel to the new location. Ouch. This is the "by the book" procedure.

  2. Retrofit ground to the old location. Have this already installed, in place, and in service. Then, after a lapse of some amount of time (other than zero), preferably with an inspector visit inbetween, then extend this circuit from the old location to the new location as 4 wires.

Here's what you can't do.

  1. nope Use the "GFCI+No Equipment Ground" trick, and then extend to the new location. Code requires new work have a proper ground, period.

  2. nope Retrofit ground to the new location. New locations must be built to current Code. You're not allowed to retrofit ground to new work.

  • @April (B) violates code because it relies on the retrofit rules to justify wiring a separate ground between the panel and new box, and the retrofit rules are to retrofit old stuff, and cannot be applied to a new box. Commented Jun 1, 2018 at 18:08
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    @April Oh! Well that would be cool and I would not have expected that. I am fuzzy on whether flexible metal conduit is a valid ground path. I know for sure that MC cable is not. Regardless, if it's flexible conduit you can simply add a green or bare #10 ground wire, and that moots the question. Conduit is designed to have wires added. Doing so doesn't even count as retrofitting! Commented Jun 1, 2018 at 18:14
  • Yes, the distinction being in MC cable, the wire is packed tightly inside the jacket often with paper filler, it's just basically cable with metal instead of plastic jacket. Metal conduit has a lot of extra space and the wires are free to move and slide. MC is not a valid grounding path. Commented Jun 1, 2018 at 18:25
  • @Harper -- paper filler would be seen on a type AC cable. Type MC uses a polypropylene assembly tape instead. Commented Jun 1, 2018 at 22:23

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