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I just moved into an old home that has a three pronged wall jack as shown below:

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I have a newer dryer that has a four pronged wire. Please see the back of the dryer, I've removed the four pronged wire.

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Question

I bought a new three pronged wire from home depot. Can I put that wire into this dryer and simple connect it to the wall? Is that safe? Will it work? If so, what do I do about the spot for the grounding wire? I would love to see a video/image of this being done.

In the past I've replaced a three pronged wire with a four pronged wire in a dryer and successfully connected it. But this time I'm trying to do the reverse..


I've fixed and already washed one round of clothes. Hopefully all is well :)

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On a side note, that receptacle looks like a NEMA 10-50R which is rated for 50A and is typically used for electric ranges. You might have trouble finding a "dryer" cord that fits, since dryers typically use NEMA 10-30 (14-30 for 4 prong) (rated for 30A). –  Tester101 Feb 25 '13 at 16:08
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3 Answers 3

What you are doing is done all the time, and there is no problem with it, if done properly. The fact is these 3 prong receptacles still exists in many older homes, and there is no requirement to upgrade an entire circuit simply to plug in a device. If you go out and purchase a new electric dryer, the seller will ask if you have a 3 or 4 prong receptacle. They will then sell you the appropriate cord, based on your answer (if you don't know, they'll probably sell you both and tell you to return the one you don't need, or offer their instillation services).

RTFM

If you check the manufacturers installation instructions, there should be a procedure for connecting the dryer to a 3 prong receptacle. The procedure can very from manufacturer to manufacturer, so make sure you check the documentation for your specific dryer.

From a random whirlpool manual:

This dryer is manufactured ready to install with a 3-wire electrical supply connection. The neutral ground conductor is permanently connected to the neutral conductor (white wire) within the dryer. If the dryer is installed with a 4-wire electrical supply connection, the neutral ground conductor must be removed from the external ground connector (green screw), and secured under the neutral terminal (center or white wire) of the terminal block. When the neutral ground conductor is secured under the neutral terminal (center or white wire) of the terminal block, the dryer cabinet is isolated from the neutral conductor.

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Here is the applicable code section:

2011 NEC Article 250 Grounding and Bonding

VII. Methods of Equipment Grounding

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.

  • 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.

  • The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.

  • 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.

  • Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.

Here is the handbook commentary:

The exception to 250.140 applies only to existing branch circuits supplying the appliances specified in 250.140. The grounded conductor (neutral) of newly installed branch circuits supplying ranges and clothes dryers is not permitted to be used for grounding the non–current-carrying metal parts of the appliances. Branch circuits installed for new appliance installations are required to provide an equipment grounding conductor sized in accordance with 250.122 for grounding the non–current-carrying metal parts.

Prior to the 1996 Code, use of the grounded circuit conductor as a grounding conductor was permitted for all installations. In many instances, the wiring method was service-entrance cable with an uninsulated neutral conductor covered by the cable jacket. Where Type SE cable was used to supply ranges and dryers, the branch circuit was required to originate at the service equipment to avoid neutral current from downstream panelboards being imposed on metal objects, such as pipes or ducts.

Caution should be exercised to ensure that new appliances connected to an existing branch circuit are properly grounded. An older appliance connected to a new branch circuit must have its 3-wire cord and plug replaced with a 4-conductor cord, with one of those conductors being an equipment grounding conductor. The bonding jumper between the neutral and the frame of the appliance must be removed. Where a new range or clothes dryer is connected to an existing branch circuit without an equipment grounding conductor, in which the neutral conductor is used for grounding the appliance frame, it must be ensured that a bonding jumper is in place between the neutral terminal of the appliance and the frame of the appliance.

The grounded circuit conductor of an existing branch circuit is permitted to be used to ground the frame of an electric range, wall-mounted oven, or counter-mounted cooking unit, provided all four conditions of 250.140, Exception, are met. The exception can be applied only where the existing branch-circuit wiring method does not provide an equipment grounding conductor. There are many existing branch circuits in which nonmetallic sheath cable with three insulated circuit conductors and a bare equipment grounding conductor was used to supply a range or clothes dryer. The bare equipment grounding conductor was simply not used because it was permitted to ground the equipment with the insulated neutral conductor of the NM cable. This “extra” conductor results because the bare conductor in a Type NM cable is to be used only as an equipment grounding conductor and cannot be used as a grounded (neutral) conductor in the same manner as is permitted for the uninsulated conductor in Type SE cable.

In addition to grounding the frame of the range or clothes dryer, the grounded circuit conductor of these existing branch circuits is also permitted to be used to ground any junction boxes in the circuit supplying the appliance, and a 3-wire pigtail and range receptacle are permitted to be used.

Exhibit 250.55 shows two examples of existing installations in which Type SE service-entrance cable is used to supply ranges, dryers, wall-mounted ovens, and counter-mounted cooking units. Junction boxes in the supply circuit are also permitted to be grounded from the grounded neutral conductor. In the bottom diagram the service-entrance cable installed from the feeder panelboard to the range or clothes dryer outlet contains an insulated grounded conductor to prevent incidental contact between the conductor and metal enclosures. Such contact could result in current being introduced onto circuit paths other than on the intended path, which is the grounded (neutral) conductor.**

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I have Moved a dryer with a four conductor cord into my home that has a 3 prong outlet. The outlet provides 240V and 120V. The house wiring for the circuit provides the two hots, the neutral, and a ground wire. the ground wire is bonded to the outlet box. I replaced the cord with a 3 prong plug and attached an external ground wire to the connection of the fourth cord wire (ground) and bonded the other end of the external ground wire to the ground wire in the outlet box. I left the internal bond wire where it was for the four wire cord. This installation IS directly equivalent to the four prong installation.

As you can see, these two circuits are the same.

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This installation is definitely NOT "directly equivalent to the four prong installation". Also, you DO NOT "connect an external ground wire"! The neutral in the 3-wire cord also serves as the ground since you must leave the bond in p0lace inside the dryer. –  Speedy Petey Jun 2 at 10:38
    
NO SIR. Neutral and ground are not same thing. They may be connected at the main breaker box, but they serve two different purposes. Neutral is the designated return path for the hot wires, while ground is fail safe return path for stray current in the event that a hot makes contact with the frame of metal appliance. The four wire installation has a ground wire integral to the cord, while the 3 wire with external ground supplies the exact same thing. The picture provided in the post above shows how to do this. (H+H+N+G) = (H+H+N)+(G) simple math! Always bond appliances to a good ground. –  Posted by another Tim Jun 8 at 3:09
    
Tim, please do NOT explain this to me. I am WELL aware of how it works and you are wrong. A 3-wire dryer cord DOES NOT use or require an "external ground". This may have been acceptable for a while many years ago but it is NOT acceptable now. A 3-wire dryer cord has the neutral bonded to the dryer case internally. The neutral DOES/DID serve both purposes. This exception was removed from the code several cycles ago which is why 4-wire dryer cords, with a dedicated equipment ground, are now required. –  Speedy Petey Jun 8 at 12:26
    
See post above for proof. –  Speedy Petey Jun 8 at 12:38
    
@SpeedyPetey I have read the above and totally agree. What I have done is the equivalent of a four wire system. I have used a three wire cord for the current carrying and have an external ground wire. It is wired exactly like it has a four wire cord attached. the ground wire is bonded to the ground wire present in the outlet box and connects to ground wire on the frame as per instruction manual. I am not using the neutral as the ground. How is it any different? –  Posted by another Tim Jun 8 at 21:24
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