4 Prong Dryer Plug - 3 Wire Receptical

nuckphotoAugust 9, 2009

I have read past posts about similar problems, but none seem exactly like mine. I have a 4 prong plug on my dryer and the wall outlet is for three. The outlet has a black, red & bare ground wire. The other posts I've read always mention a red wire as well. No red here, just black, white and ground.

Can a three prong cord work on this dryer?

Thanks for any help.

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normel

The black/white/bare is not and never has been an approved wiring method for a dryer or range. You must change the receptacle wiring to a four wire cable (black/red/white/bare).

    Bookmark   August 10, 2009 at 9:11AM
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nuckphoto

OK, thanks for the info, but at one time, 1982, it must have passed inspection. And the old dryer with a three prong plug worked just fine. Please explain the problem so I can understand what's going on.

It's 10 ga. wire on a 240v/30 amp circuit.

Also, correction in the third sentence of my OP. It should read: The outlet has a black, white & bare ground wire.

    Bookmark   August 10, 2009 at 9:25AM
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brickeyee

You have an old 3 wire 240 V receptacle, fed with a 2 wire with ground cable.
The white wire should have been re-marked as a hot (black tape).

Change the dryer cord to a 3-wire to match the receptacle.

    Bookmark   August 10, 2009 at 9:29AM
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nuckphoto

Thank you. I'll make the changes and mark the wire.

    Bookmark   August 10, 2009 at 10:37AM
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hendricus

If this is a new dryer you should read the instructions and see what it says about electrical hookup. I installed a new range two years ago and that came with instructions for 3wire and 4wire hookups.

    Bookmark   August 10, 2009 at 11:15AM
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Billl

nuckphoto - just so you know the basic setup, the live feed is coming in 2 parts. The "A" in "AC" is for alternating. The voltage goes +120, -120, +120, -120 in each line. The voltage in the 2 wires is at opposite phases. When one is at +120, the other is at -120. In the standard 120 outlets in your home, only one leg of the live and a neutral wire is running them. That means the voltage difference between live (120) and neutral (0) is 120V. In your 240 circuit, you have both legs of the live going there. That means you always have a -120 and a +120 for a difference of 240V. because both of the wires are live, you should mark them as such so nobody mistakes the white wire for a neutral.

In terms of what you should do, buying a new plug for the machine is undoubtedly the cheapest solution. That would be perfectly acceptable. You are essentially tying the ground and neutral together for the machine and it will work properly. However, the current standard is to have separate grounds and neutrals. Every appliance you buy is going to be designed that way even if you can still buy plugs to convert them back to the old 3-prong. If the area is easily accessible, you might consider getting a quote on running a new 4 wire line there and upgrading to the modern standard.

    Bookmark   August 10, 2009 at 11:43AM
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nuckphoto

Thanks Billl & Hendricus. I appreciate the explanation and may go for the re-wire. I'll have to hunt down the dryer instructions. It's about 3 years old and when we moved into this house there was a w & d already here so we used them until the remodel. I could shoot myself for not checking the plug on the newer machine but it just never occurred to me that they may be different.

Thanks to everyone.

    Bookmark   August 10, 2009 at 3:19PM
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normel

Even back in 1982, the black/white/bare was not an approved wiring method for dryers. The requirement for a three wire dryer circuit was three insulated wires with the frame of the dryer grounded to the neutral. What you have puts the neutral current on a bare conductor, and potentially, on the frame of the dryer.

    Bookmark   August 10, 2009 at 3:46PM
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petey_racer

You have to remember, even with Billl's explanation, he is still incorrect.

A dryer is NOT a 240v appliance. It is a 120/240v appliance.
It does require a neutral. Always has.
Your 10/2 with black, white and ground DOES NOT have a neutral. It is not, and never was, legal for a 120/240v dryer circuit as Normel stated early in this thread.

It passed inspection? Sure, unfortunately things like this slip by inspectors all the time.

Simply changing the cord will physically work. Is it legal or safe? No way.

If you want to do it right, legal and safe, you'll run a new 10/3 circuit, install a 4-wire receptacle and keep the 4-wire cord on the dryer.

    Bookmark   August 10, 2009 at 4:12PM
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brickeyee

"Simply changing the cord will physically work. Is it legal or safe? No way. "

It is no more unsafe than any other 3-wire dryer installation.
It is very likely the only real violation is the use of the wrong cable type for the initial installation.

    Bookmark   August 10, 2009 at 4:32PM
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Billl

Lets not be to alarmist. The thing has worked for 25 years without incident. The ground/neutral isn't insulated, but it is probably in some sheething that is keeping it from shorting into anything. It is probably safer than the millions of homes still with Knob and Tube but clearly it isn't up to modern safety standards. If you are remodeling anyway, this would be a great time to fix this issue.

    Bookmark   August 10, 2009 at 4:39PM
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petey_racer

"It is no more unsafe than any other 3-wire dryer installation. "

Sorry Brick, I 100% disagree with this statement.

A correct "3-wire" dryer installation has an INSULATED NEUTRAL and does not use the bare ground wire in NM cable as a current carrying conductor.

The only time this is not the case is when SEU cable was used.
The reason SEU was allowed is because the bare wire in SEU cable IS a neutral and IS intended to carry current.

    Bookmark   August 10, 2009 at 4:42PM
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petey_racer

" The thing has worked for 25 years without incident."

I always laugh when people write/say things like this.

Sorry bud, it still does NOT make it right.

    Bookmark   August 10, 2009 at 4:44PM
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pharkus

... and how much would it have raised the cost of the dryer to simply use a 240V motor and timer?

This always irks me.

Y'all are correct, a dryer ISN'T a 240V appliance. My argument, however, is that it should be. I see no legitimate reason to run 120V motors in otherwise-240V appliances.

    Bookmark   August 10, 2009 at 6:40PM
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petey_racer

That I definitely also agree with.

    Bookmark   August 10, 2009 at 6:45PM
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brickeyee

"The only time this is not the case is when SEU cable was used."

"It is very likely the only real violation is the use of the wrong cable type for the initial installation."

Reading is fundamental.
It is just as safe as using SEU.
The ground is not an undersized conductor,and it has the same amount of insulation as SEU, a single layer.

It should be replaced, but it is very far from a dangerous installation or an emergency.

    Bookmark   August 10, 2009 at 7:01PM
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petey_racer

Agreed it is not an emergency, but I still disagree that it is "far from" dangerous.
As it sits there is no danger, but if anyone messes with it there is a very real danger.

SE cable is NOT the same as NM cable.

Would you hold the same opinion if this circuit originated in a sub-panel? Even then SEU cable would not have been legal.

    Bookmark   August 10, 2009 at 7:50PM
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avongugg_hotmail_com

Question here,

I have a three wire supply inside a metal shield running to the outlet, inside it there is also a thin aluminum wire, I changed the plug from a three prong to a 4 prong the following way, please tell me if I went all wrong....

I connected the two hots red and black to hot brass connectors and the white to the neutral, because I did not have a fourth wire except that thin aluminum wire I connected it but also a bare copper wire going from the plug's green ground to the box itself, I figured that the box being connected to the shielded case and then tied to the breaker box would carry the ground, but to be extra careful I ran a ground from the shield connector just outside the box to the ground bar inside the breaker panel. I just did not want to run a wire the whole way... I thought about running a 12 gauge ground wire.... but did not...

Please let me know your opinion.

    Bookmark   February 3, 2011 at 1:10AM
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brickeyee

SE cable has only the cable jacket to insulate the bare conductors.

Adding a ground wire is generally a bad idea and requires as much work as running a new cable in most cases.

The ground needs to be run 'with' the existing cable.

The use of 3-wire hookups for ranges and dryers was just a way to save some wire.
If fed from a main panel the neutral and ground land on the same bus bar and are connected i the panel.
The risk with large conductors is very small since they have more than just a 'wire around a screw' type termination (screw clamped pressure plates are common).

    Bookmark   February 3, 2011 at 8:33AM
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Ron Natalie

I get the feeling that what you have there is type AC cable.
Presumably the existing box is metal and connected to the AC cable sheath properly. In these assumptions are correct, then it the armor can be used as the ground as you appear to OK.

    Bookmark   February 3, 2011 at 8:48AM
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weedmeister

Are you saying you had 4 wires, black, red, white and bare aluminum?

    Bookmark   February 4, 2011 at 7:48AM
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brickeyee

While dryers and ranges have typically been 120/240 V loads there is a long standing exception allowing the use of 3-wire circuits.

The exception still allows the use of the older 3-wire circuits and almost all ranges and dryers come with instructions for either installation.

The change to the exception is that it is now strictly a 'grandfather' exception.
All new circuits must be 4-wire, and if any changes are made to a 3-wire circuit it must be changed to 4-wire.

Many ranges and dryers do not even come with a cord attached, but one is purchased to match the circuit in the house the unit will be installed in.

The difference in the equipment is usually the removal of a bonding screw between the neutral terminal and the chassis.

A 3-wire installation bonds the neutral to the chassis for safety, while a 4-wire uses the ground in the circuit to ground the chassis.

The wire resistance is low enough that having a neutral grounded chassis for the small 120 V loads (motor and timer typically) does not produce enough voltage drop in the wiring to be detected by people (the chassis has a voltage equal to the voltage drop in the neutral leg present).

    Bookmark   February 4, 2011 at 9:18AM
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