Wiring 3-prong dryer to 4-conductor circuit

[Stephen Tashiro]

What's the safest way to re-wire a situation where a clothes dryer has a 3 prong cord and the receptacle for it is designed for a 4 prong cord? The ground on the receptacle is good. Is it best to change the receptacle to 3 prong and not connect the ground? - or is it best to change the cord on the dryer?

The particulars of the situation:

Maytag Model MEDP576KW1 purchased used. Hasn't been plugged-in yet. Reliable local business says it works.

Meter readings with the dryer unplugged show that the disconnected terminal on the white wire (on the left of photo) connects the chassis to the neutral when the terminal is screwed onto the chassis. The wire is internal to the dryer, not part of the cord. This terminal was connected to the chassis when the dryer was delivered. When it is disconnected there is an open circuit between the neutral and the chassis. So it seems that the white wire can serve as a ground,

[Tom M King]

It's the neutral you don't need, not the ground. Both go back to the ground somewhere in the system, but I'd connect the ground. If there is an arc fault breaker somewhere with shared neutrals somewhere, it would be one of those problems impossible to find later.

[Bruce Wrenn]

It's the neutral you don't need, not the ground. Both go back to the ground somewhere in the system, but I'd connect the ground. If there is an arc fault breaker somewhere with shared neutrals somewhere, it would be one of those problems impossible to find later.

Tom, this is the first time you and I don't agree, The neutral is necessary for the timer and motor to operate on 110. Simplest thing to do is buy a four wire cord set, and connect it to screws on strip on dryer. Connect ground to frame somewhere. Most likely there is a wiring diagram some where on back of dryer showing how to do this.

[Tom M King]

I'm just seeing three lugs on that dryer, like ours. I didn't look up anything about that particular model of dryer. I might be misunderstanding something.

edited to add: I found the manual, but no information in it about connecting the cord. Looking down at the parts, the cord they sell for it is a three conductor cord.

https://www.searspartsdirect.com/pro...-026/id-pt220l

[Doug Garson]

Here's the wiring diagram for that model, maybe it will answer your question.https://appliantology.org/gallery/im...ce-in-autodry/

[Thomas McCurnin]

Arc Faults are not wired to the shared Neutral bus bar and instead are wired directly to the breaker, unlike other breakers which simply has a hot wire on both sides. The Arc Fault will have both a pair of hots on each end and a neutral.

[Bruce Wrenn]

I'm just seeing three lugs on that dryer, like ours. I didn't look up anything about that particular model of dryer. I might be misunderstanding something.

edited to add: I found the manual, but no information in it about connecting the cord. Looking down at the parts, the cord they sell for it is a three conductor cord.

https://www.searspartsdirect.com/pro...-026/id-pt220l

Three wire cord sets for dryers or stoves have never been allowed on mobile homes. This is because the frame of the home could become energized. Stand on the ground, and reach for the doorknob-ZAP! Four wire has been in the NEC for all structures for years, 1996 to be exact. Last house I built (1992,) if the dryer or stove was fed using SE cable, then three wire was permitted, but if Romex was used it had to be four wire. Go figure. For this dryer, you hook up four wire if it was three wire, and then bond ground wire to frame. Dryer must be old, as these has been standard practice for at least thirty years or more. Maytag has an excellent video showing how to connect four wire cord set to dryer with three wire terminal block. Step by step instructions

[Stephen Tashiro]

Someone on physicsforums.com found an applicable Maytag manual with wiring instructions for a 4 wire cord. ( https://www.maytag.com/content/dam/g...07405-reva.pdf ). So the dryer was designed to take a 4 wire cord after all. It says to attach the terminal of the white wire to the neutral post (along with the neutral of the cord) and attach the ground of the cord to the chassis where the white wire was formerly attached. That makes sense according to my measurements of connections.

[Tom M King]

Arc Faults are not wired to the shared Neutral bus bar and instead are wired directly to the breaker, unlike other breakers which simply has a hot wire on both sides. The Arc Fault will have both a pair of hots on each end and a neutral.

I was talking about shared neutrals anywhere else in the system. Since a dryer is on a separate circuit, it shouldn't matter. Wiring so that neutrals were shared was a very common practice for a long time, before the days of Arc Faults and even Ground Faults. They would just tie all the neutrals together. Back when Ground Fault circuits were first required, electricians commonly ran everything the same way with shared neutrals except for the ground fault circuits that used a ground fault breaker. The current on the hot and neutrals have to balance coming back to the breaker or these breakers will trip. That's why the neutral wire comes back to the breaker, and then the breaker pigtail wire goes to the neutral bar.

Thanks Bruce. Nice to learn something. I can see where it could be a problem if the grounding/grounded wire became loose. It would be very important to make sure this is a strong connection on dryers using old 3 wire circuits. I remember when we had to start furnishing four wire circuits for dryers, but there are many, including in our house, newer dryers running on old 3 wire circuits. I had never spent any time thinking about it beyond that. I think the next time we replace a dryer, I'll run a new 4 wire circuit. In our rental house, it would be about impossible to change it without a great deal of work.

[Bill George]

Someone on physicsforums.com found an applicable Maytag manual with wiring instructions for a 4 wire cord. ( https://www.maytag.com/content/dam/g...07405-reva.pdf ). So the dryer was designed to take a 4 wire cord after all. It says to attach the terminal of the white wire to the neutral post (along with the neutral of the cord) and attach the ground of the cord to the chassis where the white wire was formerly attached. That makes sense according to my measurements of connections.

This is the correct way, the using grounding wire or green as a neutral for the dryer controls and motor was outlawed in the NEC 30 years ago.

[Tom M King]

I couldn't remember when it was, other than in the mid '90's. "30 years ago" sounds like a lot longer ago than "mid '90's". It's strange that I never heard about it, or thought about it since then. It must not have presented many problems since a dryer is on a separate circuit.

edited to add: I always wondered why it was less trouble for them to sell dryers without cords than to simply install them to start with. I understand completely why it's less trouble now.

[Bill George]

So 1993 is 30 years ago, I do not recall the exact date but when I tested for my Masters in 2005 it was in that Article 250.142B and it was not marked as New so it happen prior to that 2005 book. I can not find my older Code books.

When I remodeled our kitchen and replaced the stove, I ran a #10 wire well protected in the basement ceiling over to the main panel ground buss and then wired in the proper 4 wire receptacle for the new stove.

[Tom M King]

When I was building and selling new houses, I never included appliances, so I never got past putting in a four wire circuit after the code change, and never installed a four wire dryer. I didn't give it any thought past that. I don't remember the exact date of the change either, but I know all the houses I built in the '70's, '80's, and I think into the early '90's had three wire dryer circuits. I'll bet the reason they don't include the cord is so the installers can keep both on the truck, and use whichever cord fits what receptacle they find.

[Bill George]

There is some sort of exception for older houses (mine was built in 1963) but I just ignored that and ran the ground wire as I like to do things right.

[Bruce Wrenn]

I'll bet the reason they don't include the cord is so the installers can keep both on the truck, and use whichever cord fits what receptacle they find.

Or use the one off the old dryer. Seldom are they unplugged, so there is no wear. The last dryers I installed for clients, included a bonding strap to be use to bond frame to neutral if there was a three wire plug for dryer. FYI, Habitat Restores are an excellent source for dryer cord sets (30 amp,) not so for stove (50 amp) cord sets. Don't know why, but seldom do I see 50 amp cord sets. Need one a few years back to make a portable sub panel for a travel trailer.