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In my apartment, I have a 4 wire 240V receptacle for a dryer where the neutral is not connected, only the 2 hots and ground. Is this configuration permitted for a dryer circuit? An electrician and maintenance person have both said the circuit is fine, but the electrician did point out that there is no box for the receptacle. How can the dryer get the necessary 120V to operate the panel and the other small parts in the dryer?

  • Please focus on the question without writing a story. – BMitch Sep 11 '13 at 21:44
  • confirmed it is 2 hots and a ground, i can upload pictures, on the back of the 240v receptacle it states green for the ground and white for the neutral. – user15043 Sep 12 '13 at 1:13
  • so basically this is what is known as an open neutral. and the response below speaks of a grounding conductor, which is a ground, and does not reference a grounded conductor, which is a neutral, which there is not in the receptacle. How does that answer below answer the question? There is no neutral in the receptacle. Please explain the answer below? Still confused there is no neutral, and i get an answer involving a grounding conductor not present which there is, a grounding conductor is the ground is it not? I do appreciate the answer, but i need an answer to a no neutral situation. – user15043 Sep 12 '13 at 10:56
  • on a 4 wire 240v NEMA 14-30 240v receptacle. – user15043 Sep 12 '13 at 11:00
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    How have to "confirmed" that it's a grounding conductor? Grounded (neutral) conductors can be fairly similar to grounding conductors. – Tester101 Sep 12 '13 at 14:17
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Here is a highlighted image of a random electric dryer schematic.

Random Electric Dryer Schematic
Click for larger view

Notice that all the control circuits are 120V components, and that basically only the heater is 240V. Extending this image further, we can see how the dryer connects to a 120/240V split-phase system using a 3 wire cord.

Random Electric Dryer Schematic attached to plug
Click for larger view

Due to the nature of the 120/240V split-phase system, the grounded (neutral) and grounding conductors in a dedicated single appliance circuit are basically the same. The dryer will work just fine whether the N terminal is connected to a grounded (neutral) conductor, or a grounding conductor. However, connecting a NEMA 14-30R device in this way is nonstandard, and a code violation.

enter image description here
NEMA 14-30R

In the case of a three wire circuit, a NEMA 10-30R device should be installed.

enter image description here
NEMA 10-30R

When the wiring is connected to the proper device, the third wire in the cable becomes a grounded (neutral) conductor, and the code may be satisfied.

If you read point number three of the exception to section 250.140 of the National Electrical Code, you'll find that the neutral must be either insulated, or part of a Type SE cable. If this is not the case, your installation may still be a code violation.

An uninsulated, normally current carrying conductor running through your walls is typically a bad thing. Which is why this code exception is only valid, if the conductor is insulated.


tl;dr

Connecting a dryer in this way will work, but is a potentially dangerous code violation (according to the National Electrical Code).

If the receptacle is not of the self-contained variety, and is not in a box. That is defiantly a code violation (NEC 2011 406.5).


Extra Information:

If a proper 4 wire cable existed, the schematic from above would look something like this...

Random Electric Dryer Schematic attached to 4-wire plug
Click for larger view


If I've missed anything, or haven't explained something properly. Feel free to ask additional questions, or point out mistakes in the comments below.

  • as you said it is a code violation and incorrectly wired. – user15043 Sep 12 '13 at 13:20
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    @user15043 It may be a code violation, and possibly incorrectly wired. – Tester101 Sep 12 '13 at 13:26
  • Is it code to go just go from a 3 wire receptacle to a 4 wire receptacle without adding the 4th wire, if there are only 3 wires? What would the purpose be since a 3 wire receptacle would have worked with 2 hots and a neutral Or is that what you were referencing by a code violation? – user15043 Sep 12 '13 at 13:27
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    @user15043 It is likely a code violation (according to current National Electrical Code) to install a 4 prong receptacle, on a 3 wire circuit. However, there are strange situations that can make this not a code violation, which is why I will not say with absolute certainty that this is a code violation. I would only be able to make that determination by actually inspecting the circuit myself. The installer probably should have modified the dryer cord, not the receptacle. – Tester101 Sep 12 '13 at 13:42
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    For your other electrical problems, it could be a bad meter, or a floating (open) neutral. It's difficult to say, when I'm an internet away. Have a local licensed Electrician investigate. If it's really at 850V, most of your electronics are surely fried, and possibly on fire. As for the exceptions in NFPA 70 (2011), start with Article 406 (Receptacles, Cord Connectors, and Attachment Plugs (Caps)), specifically 406.4(D). – Tester101 Sep 12 '13 at 18:53
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Tying neutral and ground together at the dryer is an obsolete and dangerous technique. It means you need one less wire, but if anything goes wrong with that wire, the chassis of the dryer becomes electrified. There's a special exception (NEC 250.140) that allows you to connect a dryer this way. Legal or not, this is a terrible idea. However this is the conventional advice - you do this bad idea using a NEMA 10-30 connector.

However you are much better off connecting a NEMA 14-30, with separate neutral and ground, and removing the neutral-ground tie jumper from the dryer.

Where do you get neutral? When a dryer is connected with UF cable, people often assume the bare wires wrapping around the conductors are the ground. In the past, this has been used as neutral (with no ground at all). Here's the thing. It is legal to retrofit grounds. (it is not legal to retrofit neutrals).

So if there is a bare wire in the cable and it's been used as neutral in the past, your best bet may be to continue using it as a neutral. (Make sure to wrap it with tape so it can't short against the ground or the box). And then retrofit a ground using some cheap, common #8 ground wire from the hardware store, and run that back to the panel via any reasonable route.

Now you have 4 wires in the panel and can connect the 14-30 normally.

If it's not in a junction box, get a deep 4x4" box and an appropriate lid for a 14-30 receptacle, and install it there.

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I disagree with O.P. Neutral is NOT basically the same as ground and should NOT be connected to ground (see 1 bad exception below). Also: NEC's circuit never include the appliance circuit (you never expose people to the inside of an appliance - if the appliance has a legitimate NEC ground and you connect to that: then your right).

If you have no ground (3 wires total for a 240 single phase needing 4 wires total), you have no ground: it's that simple. The neutral connects to the neutral bus NEVER the ground bus in the panel (USA typical home - you do have to check with your power company for ). see the folowing about typical power company neutral ground wiring and note some special buildings do NOT use the system even on the same power company: https://en.wikipedia.org/wiki/Earthing_system

In most areas neutral ground are NOT the same potential difference voltage (0 on average but spikes or PROBLEMS are at different differences - but more important is ground is a shortest path return to earth that trips the breaker and connections to neutral to that causes un-natural current).

See also: https://en.wikipedia.org/wiki/Floating_ground , noting none of NEC's grounds are perfect 0 potential to surroundings or to 0 at any or all times. It's just not NEC's circuit diagram to do this.

  • The one "bad exception" is that decades ago some municipalities did allow hot appliances to treat neutral and ground the same but it is NOT the safest thing to do. It's your choice if your replacing, if doing new work 4 total wires are likely required. They did this because of cost of copper and back then less people had money to consider the safety added.

Where does the ground wire go in a 3-prong dryer cord configuration?

I wish I could tell you if running 14awg 14/2 tied or 10/1 awg to add the extra ground to the panel will be successful in the end: you might well have an inspector that insist all 4 wires be in one straight jacket no matter how well ohm balanced you are and that you remove it and start over. Your doing old work so adding a ground might cause inspection failure depending on the (municipality).

One more thing OP. BONDING. Any metal or water you normally may touch (dryer, metal conduit) while using the drying should have the SAME GROUND (in the bad/wrong case: same neutral) (this is done in pools and is why you see lights in a pool but aren't shocked in water or by ladders, and never ever using neutral). Don't extending this "bonding" to "true grounds". If you have any true ground nearby one might touch (bonded or not): you really should install the 4 wire - only sain thing to do.

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Are you sure it's not two hots and a neutral, with the neutral also serving as the ground?

It is not allowed to connect the neutral to the casing of most appliances; however, the NEC specifically makes an exception for dryers:

250.140 Frames of Ranges and Clothes Dryers.
[...]
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 fol- lowing 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.

If those four conditions are met, it is allowed to attach the neutral to the casing.

See this question for more information on grounding a dryer with three-prongs.


However, you specifically stated that it's the grounding conductor that's connected to both ground and neutral. If that's true, the above exception would not apply, since the outlet box (presumably?) would have both ground and neutral running to it.

  • it is 2 hots and a ground, i can upload pictures if need be. if there were a neutral then there would be the possiblility of 120v for the electronic panels etc instead of just straight 240v – user15043 Sep 12 '13 at 1:07
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    @user15043 pictures are always helpful, thanks. – Tester101 Sep 12 '13 at 12:20
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    @user15043: The electronics, and everything else, would work fine if the third wire were ground rather than neutral. But this would be a code-violation, since it means the ground would be a current-carrying conductor. A picture would be very helpful. – BlueRaja - Danny Pflughoeft Sep 13 '13 at 2:31
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I'll bet that the dryer's cord has the ground wire connected internally to neutral and also to ground. In fact, this is how 3 wire 120/240 appliances were wired up until rather recently (2002 if I recall correctly).

Unless the breaker is a GFCI, which is highly unlikely for a dryer, the non-separate ground and neutral is a minor issue. Technically, it is probably not to code. However, that could readily by fixed by replacing the receptacle and cord with a three wire and feigning the previous state of the art.

  • So what you suggest is that this is legal and that for the apartment management to just modify it backwards. Correct – user15043 Sep 11 '13 at 22:09
  • @user15043: I don't suggest that it is 100% legal, especially if it was installed in the last few years. But it used to be legal not so long ago and I bet quite a few electrical inspectors would let it slide. – wallyk Sep 11 '13 at 22:12
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    had to delete to make sure not copyrighted – user15043 Sep 11 '13 at 22:22
  • Is there such a thing as 90% legal? – BlueRaja - Danny Pflughoeft Sep 11 '13 at 22:26
  • @BlueRaja-DannyPflughoeft Yes, ask any politician. – Tester101 Sep 12 '13 at 13:25
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120 plus 120 = 240. Your panel has 120 AC on each side. AC stands for alternating current. A wave, not a line. Opposite sides of your panel have opposite wave signatures allowing the "hot" for one 120 to function as the neutral for the other.

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