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#98887 - 06/21/06 06:58 AM Dryer wiring 3-wire vs. 4-wire
Bill39 Offline
Member

Registered: 11/28/01
Posts: 77
Loc: Indianapolis, IN, USA
Please comment on the advice I gave to my friend about a problem he ran into this weekend and let me know if it was correct or if there was another alternative.

My friend and his brother traded home clothes dryers (don’t ask why) but now there was a 220V plug configuration problem. NOTE: this is in the USA.

My friend now has a 3-wire outlet and a dryer with a 4-wire male plug.
The brother now has a 4-wire outlet and a dryer with a 3 wire male plug.

He wanted to just put a 4-wire cord on the 3-wire dryer and a 3-wire cord on the 4-wire dryer (tying the ground and neutral together).

My advice was that my friend needed to install at his house a 4-wire outlet and run 4-wire Romex to it.
My advice to fix the problem at his brother’s house was to replace the existing 4-wire outlet with a 3-wire outlet connecting the ground and leaving the neutral wire disconnected at the outlet.

Right/Wrong/Alternatives?????

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#98888 - 06/21/06 09:52 AM Re: Dryer wiring 3-wire vs. 4-wire
Elviscat Offline
Member

Registered: 08/13/05
Posts: 214
Loc: Seattle Washington USA
"My advice to fix the problem at his brother’s house was to replace the existing 4-wire outlet with a 3-wire outlet connecting the ground and leaving the neutral wire disconnected at the outlet."
If you were to do this it would result in current on the ground wire which is definetley not code legal. if he already has a four-wire plug just replace the cord, it's reletively cheap and inexpensive. Just open the back of the drier up, remove the N/G bond, hook ground/ground Neutral/Neutral and you have a code compliant installation.

-Will

(edited for spelling)

[This message has been edited by Elviscat (edited 06-21-2006).]

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#98889 - 06/21/06 10:06 AM Re: Dryer wiring 3-wire vs. 4-wire
Roger Offline
Member

Registered: 05/18/02
Posts: 1779
Loc: N.C.
They just needed to swap the cords when they traded.

Roger

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#98890 - 06/21/06 12:22 PM Re: Dryer wiring 3-wire vs. 4-wire
Bill39 Offline
Member

Registered: 11/28/01
Posts: 77
Loc: Indianapolis, IN, USA
I thought the 3rd wire on a 220VAC dryer outlet was a "ground" not a "neutral"?

So you're saying it is OK to tie the neutral and ground together inside the dryer?

Isn't there a good reason a 4th wire is on the newer dryers and would therefore need a 4-wire outlet?

I completely understand the difference between ground wire and a (grounded) neutral and that a true ground wire should not carry any current unless there is a fault.

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#98891 - 06/21/06 02:42 PM Re: Dryer wiring 3-wire vs. 4-wire
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
OK, here goes. Bill, you probably already know this, but there are some reading this board that do not, so I will be overly simple for their benefit.

In the "old days" dryers and ranges had two "hot" wires, and a third that served both as a ground, and as a 'neutral' for incidental 120v. loads (light, timer, etc.) On these machines, there was a strap that connected the case of the appliance to the third wire.

For a variety of reasons (too involved to get into here), we separate the "ground" from the "neutral" back at the main panel. Simply put, the neutral wire is intended to always be carrying current, and to become "hot" if it comes loose.... while the ground is never intended, under normal circumstances, to be carrying current. It's just there, in case something bad happens.

So, dryers and ranges now get plugs with four prongs, and, in the case of romex, are hooked up to four wires. These units DO NOT have the case connected to the "neutral."

The correct solutions are:
1) The guy with the four-wire plug gets to run a four-wire cable to his outlet, and replace the receptacle; and,

2) The guy with the three-wire plug gets to replace it with a four wire cord..AND remove that 'bonding' strap in the back of the appliance.

This is one situation where it will 'work' even if it's NOT OK.

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#98892 - 06/21/06 03:14 PM Re: Dryer wiring 3-wire vs. 4-wire
Roger Offline
Member

Registered: 05/18/02
Posts: 1779
Loc: N.C.
Bill, there is no reason to change a three wire circuit to a four wire if the three wire circuit was compliant when the house was built, and assuming this is the case is the reason they just needed to swap cords with each other.

Just because you might have an older house and buy a new appliance doesn't mean you would have to rewire the house. Note the Exception to 250.140

 Quote:
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 grounded 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 grounded 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.


Roger




[This message has been edited by Roger (edited 06-21-2006).]

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#98893 - 06/21/06 04:25 PM Re: Dryer wiring 3-wire vs. 4-wire
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
Roger, my concern over replacing the four-prong plug with a three-prong type is that the case bond must also be replaced; it was likely removed when the cord was attached. I'd hate to see the case become ungrounded.

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#98894 - 06/21/06 04:53 PM Re: Dryer wiring 3-wire vs. 4-wire
Roger Offline
Member

Registered: 05/18/02
Posts: 1779
Loc: N.C.
John, I can see your concern but, whoever would change the cords should know what they are doing, especially if they were knowledgeable enough to be considering installing a new circuit.

If they hired an electrician to do this work, the electrician should tell them their options before installing and charging for a new circuit IMO.

Roger

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#98895 - 06/21/06 06:33 PM Re: Dryer wiring 3-wire vs. 4-wire
mister h Offline
Member

Registered: 05/26/06
Posts: 20
Loc: erie, pa. usa
Don,t forget about the UL listing of the appliance.
_________________________
ken

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#98896 - 06/21/06 07:18 PM Re: Dryer wiring 3-wire vs. 4-wire
mister h Offline
Member

Registered: 05/26/06
Posts: 20
Loc: erie, pa. usa
And remember the old saying "it worked fine at the other house."

Have to watch the the liability.
_________________________
ken

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