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We moved to a new place where the dryer connection is 3-prong instead of 4-prong. The dryer was originally 4-prong, so we bought a 3-prong cord and installed it. It works fine, except I am not entirely sure if I installed the ground wire correctly.

Originally, there was a green wire on the cord itself, and that was connected to the screw on the top of the first picture. This is, I assume, used to ground the case and prevent shocks when touching the exterior of the dryer.

Now with the 3-pronged plug, there is no ground wire on the cord. So where does the existing green wire in the case go? Do I leave it where it originally was like in the first picture or do I connect it to the central terminal like in the second picture?

enter image description here

enter image description here

There's no bonding strap running from the case to any terminal. I can't tell where the green wire is connected to.

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Duplicate: diy.stackexchange.com/questions/25510/… –  Kaz Aug 10 '13 at 2:18
    
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2 Answers

up vote 6 down vote accepted

DO NOT connect the ground wire to the grounded (neutral) conductor, as this could lead to current flowing through the body of the dryer (and potentially through you).

The installation guide for the dryer will have wiring instructions for both 3, and 4 wire configurations. Check the manufacturers documentation for proper wiring, but I would say the first image is likely correct.

enter image description here


Instructions from random Maytag Installation Instructions (PDF)

3 Wire Cord

3-Wire Instructions

4 Wire Cord

4-Wire Instructions


Update:

After doing some research, and looking at dryer wiring diagrams. It turns out that the green/yellow wire is not a ground wire, it is a neutral to case bonding wire. When this wire is not in use (in a 4-wire installation for example), it is simply connected to the neutral terminal and is unused.

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Well, in his second image he's connecting the ground-wire to the neutral-wire, not the body of the dryer to the neutral. So (unless there's a loose wire that would actually require the safety of the ground) that will likely just trip the GFCI when he tries to turn the dryer on. –  BlueRaja - Danny Pflughoeft Aug 9 '13 at 17:12
    
@BlueRaja-DannyPflughoeft Maybe. I'm assuming the green/yellow wire in the image is connected to some internal components of the dryer. So by connecting it to the grounded (neutral) conductor, you're providing an alternative path to ground through anybody that touches the dryer (or whatever internal parts are bonded to this green/yellow wire. This assumption may be wrong. –  Tester101 Aug 9 '13 at 19:48
    
It turns out we were both wrong, and your update is correct - the green-yellow wire is not a grounding wire, it's actually connected to the neutral. This allows the dryer to be grounded even when you don't have a dedicated ground wire. This is, surprisingly, allowed by the NEC. (also, I now know that most dryer's don't have GFCI's, because dryer-GFCI's are insanely expensive) –  BlueRaja - Danny Pflughoeft Sep 11 '13 at 22:55
    
@BlueRaja-DannyPflughoeft That's what I said. –  Tester101 Sep 12 '13 at 12:07
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My previous answer stated that dryers with three-prongs are ungrounded, which is dangerous. This is incorrect. Dryers with three-prongs are grounded using the neutral wire, when hooked up correctly (see @Tester101's answer for info on how to do that).

Normally grounding a device via the neutral wire is not allowed. However, the NEC specifically makes an exception for ovens and 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.

It's important to note that this means on many (all?) dryers, the green grounding-wire should not be connected to the grounding screw when using a 4-prong wire, only with a 3-prong wire! So, make sure to find and follow the directions for your dryer when installing a new cord!

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