3-wire dryer receptacle outlet

[Jeff Eastman]

.............

[Rick Cantrell]

Not 100% sure
New dryers are 4 prong
Older dryers were 3
Same for stoves

Most of the appliances that use 220 also have 110 circuits for the clock, and controls. In the past you would get the 110 off one leg and the ground, now with 4 prong you have a neutral and ground.

So 3 prong outlet was correct, but should be changed to 4, if possible, may only have 3 wires.
It does not HAVE be be changed to 4. but would be better as 4.

[John Arnold]

I'm sure you will, but pipe up if I'm wrong!

The 3-wire dryer receptacle outlets have one wire serving both as a neutral and an equipment ground. I consider this as a safety hazard and have been putting this a repair item in my reports. The electrician said it was okay and not a safety hazard. I think I'm right but will swallow my already beaten up pride if I must.

Ask electrician why they are now required to be 4-wire, if 3-wire is ok.

[Phillip Stojanik]

The four prong outlets with four wires are electrically safer. As Rcik points out though, you have to have four wires present if you want to upgrade to the 4 prong outlet (or be willing to run a new wire).

The reasons that the four prong outlets are safer is the same reason you need a four wire feeder to electrical panels downstream of the service equipment. The only interconnection between the ground and neutral you want in your electrical system is at the service equipment.

[Bob Mayer]

I believe the change from three to four wires started with the 1996 NEC.

In the three-wire system there are (at least) two possible problems.

1. There is relatively high resistance in the neutral line. To the extent that the neutral is carrying significant current (think the 115V drum motor in a dryer) there will be a voltage on the appliance frame equal to the voltage drop in the neutral line.

2. There is an open in the neutral line. If one of the 115V devices is turned on you could have close to 115V on the appliance frame. This situation is why the neutrals on receptacle outlets in split circuits are required to be pigtailed and not just daisy-chained through the device.

That said, the NEC folks took their sweet time to finally disallow 3-wire circuits, I guess there were few problems in real life.

If the circuit were run before the 1996 NEC took effect I would make a comment, but say that upgrading is not required. If the circuit war run when the new rule was in force I would have a problem with that.

- BOB

[Jerry Peck]

The electrician said it was okay and not a safety hazard.

That answer (to some extent), as some have already pointed out, is that of timing.

The answer (to the rest of the extent) is that the electrician is wrong, and, depending on what you said and your wording, you may also be wrong.

First, let's take what the electrician said: "The electrician said it was okay and not a safety hazard."

"The electrician said it was okay ... "

It was, for eons.

" ... and not a safety hazard." I was always a safety hazard. Always was, and, until those old ones are changed, always will be.

No "upgrade", as Bob called it, is *ever* required. If the circuit 'should have been' run with 4 wires, then it 'shall' be replaced, meaning it is wrong, dead wrong.

If the circuit 'was not required to have been' run with 4 wires, then it 'should' be replaced, meaning it is safer to replace it, however, *IF* it is a 3 prong plug for the range or dryer, *IT IS* most likely only wired with 3 wires, meaning that correcting it may not be real easy - all depends on where the dryer is located in relation to the panel.

So, depending on 'how' you write them up, you could be right, or just partially right.

[Scott Patterson]

I don't have an issue with it, nor do I report if it is a 3 or 4 wire equipped receptacle. I don't consider a 3 wire system a safety issue either. But this is me, and your opinions may differ.

[Rick Cantrell]

That brings up a question.
You buy a house with the 3 prong outlets, and your stove and dryer are the newer 4 prong style. Is it allowed ( by code and/or manufacture) to install a 3 prong cord on the stove, dryer?

[Bob Mayer]

That brings up a question.
You buy a house with the 3 prong outlets, and your stove and dryer are the newer 4 prong style. Is it allowed ( by code and/or manufacture) to install a 3 prong cord on the stove, dryer?

I do not know, but I believe that the answer is yes. Buying a new appliance does not require running a new cable from the panel to the receptacle outlet.

- BOB

[Jerry Peck]

Bob,

Rich said this:


That brings up a question.
You buy a house with the 3 prong outlets, and your stove and dryer are the newer 4 prong style. Is it allowed ( by code and/or manufacture) to install a 3 prong cord on the stove, dryer?

Which means those circuits already 'have' the four prong receptacle, and, presumably, four wires.

You said:

I do not know, but I believe that the answer is yes. Buying a new appliance does not require running a new cable from the panel to the receptacle outlet.

In answer to Rick's questions, if the receptacles are already four prong, then a four conductor cord and plug would be needed to install the range or dryer.

I'm guessing that is what the manufacturer's installation instructions will say, and the code does not say that you may change the receptacle out to a three prong type from a four prong type. (But I could be wrong, I've been wrong before.)

[Rick Cantrell]

Jerry
Thanks for answering, but you misread my question.
3 prong receptacles
4 prong cord

[Jerry Peck]

Jerry
Thanks for answering, but you misread my question.
3 prong receptacles
4 prong cord

Man I sure did. I must be losing my mind??? Can't seem to read anymore.

[Scott Patterson]

One of the reason that dryers and stoves don't come with the connecting wire and plug.

[Tim Moreira]

A few years ago I bought a new dryer. The appliance company came out and installed the dryer. The dryer did not have a cord on it already. I noticed they brought with them both cords, 3 and 4 prong to use accordingly.

[Tim Moreira]

What difference does it make if you have a 3 or 4 wire dryer if both of the wires go back to the *Service Equipment* panel and are bonded together there anyway.

Now if the go back to a panel that is not *Service* then I would agree.

Am I looking at this correctly or not???:confused:

[Bob Mayer]

What difference does it make if you have a 3 or 4 wire dryer if both of the wires go back to the *Service Equipment* panel and are bonded together there anyway.

Now if the go back to a panel that is not *Service* then I would agree.

Am I looking at this correctly or not???:confused:

There are two possible problems, which I mentioned in an earlier post.


I believe the change from three to four wires started with the 1996 NEC.

In the three-wire system there are (at least) two possible problems.

1. There is relatively high resistance in the neutral line. To the extent that the neutral is carrying significant current (think the 115V drum motor in a dryer) there will be a voltage on the appliance frame equal to the voltage drop in the neutral line.

2. There is an open in the neutral line. If one of the 115V devices is turned on you could have close to 115V on the appliance frame. This situation is why the neutrals on receptacle outlets in split circuits are required to be pigtailed and not just daisy-chained through the device.

That said, the NEC folks took their sweet time to finally disallow 3-wire circuits, I guess there were few problems in real life.

If the circuit were run before the 1996 NEC took effect I would make a comment, but say that upgrading is not required. If the circuit war run when the new rule was in force I would have a problem with that.

- BOB

In case 1. the problem is that the "ground" is also the neutral, there is current flowing through it, and the voltage at the "ground" point on the appliance frame is not the ground potential at the service because of voltage drop. With four conductors this is not a problem, because there is no current flowing through the ground conductor. The voltage here would probably be small, but real.

In case 2. we violate your assumption "if both of the wires go back to the *Service Equipment* panel". If there is a break in the neutral circuit, There could be almost 115V on the appliance frame. This is a similar problem to losing the neutral on a split circuit or on the service except here the neutral, with the far from zero voltage, is on the appliance frame. (A friend called me out for an electrical problem last autumn, weird voltages all over. The neutral was open at the transformer.)

- BOB

[Bob Mayer]

What difference does it make if you have a 3 or 4 wire dryer if both of the wires go back to the *Service Equipment* panel and are bonded together there anyway.

Now if the go back to a panel that is not *Service* then I would agree.

Am I looking at this correctly or not???:confused:

"Now if the go back to a panel that is not *Service* then I would agree."

The only difference that makes is that the resistance in the neutral may be higher (case1.) and there are more points of failure for the neutral (case2.) In a properly (other than being 3-wire instead of 4-wire) operating system, it does not matter if the panel to which the circuit is connected is the service or not.

- BOB

[John Steinke]

It's not really an "either/or' issue.

The old style ... neutral bonded to the appliance, three wire plug ... was, for the most part, safe enough. There was, nonetheless, a drive to change from this to the four wire plug, and with the neutral isolated from the case of the dryer.

Earlier dryers had no need for a neutral ... everything was 240v- switches, timers, and all. For reasons on economy, manufacturers were able to use 120v timers, etc .... by simply using the appliance case as a neutral, as well as ground.

Sure, the code says 'no objectionable current on the ground." Care to define 'objectionable?'

For reasons that had absolutely nothing to do with dryers, the electrical trade began to recognize the need to connect the ground to the neutral at only one place- and that place was the service entrance. Many problems, many dangers, were corrected once this was done. Yet, we still had those three-prong plugs on the dryers and ranges.

Still, for the typical romex-wired home, the "parallel path" created with this second neutral / ground connection was pretty much a non-issue. Make that a house wired in pipe, add a loose connection, have the dryer 'on' ... and you now have a section of the pipe that's "hot." Not a good situation.

For the sake of consistency, it was decided to change over to four-prong plugs.

More important than the type of plug is that the appliance be wired correctly for the plug that is used. If a four prong plug is used, yet the case is still bonded to neutral, this situation can still develop.
The reverse situation is even more dangerous ... a three prong plug on an appliance whose case is not bonded. That could allow the case to become "hot."

[James Duffin]

I believe 4 wire plugs for dryers and ranges was the code for mobile homes years before it was for code for non-metal housing. The more grounding paths the safer it should be in theory...

[Rick Cantrell]

Calling it a repair, I don't think so. Though you might mention it has a 3 wire plug.

Kinka of like 2 prong ungrounded receptacles. Calling to replace all the wiring is not the answer, making a notation that there are 2 prong outlets would be.

[Rick Cantrell]

The Dryer (and/ or oven) outlet are wired for a 3 prong cord, for added safety newer homes have been wired with outlets that use a 4 prong plug. If your appliance cord does not match the outlet, have a qualified appliance repairman install the correct cord.

[Tim Moreira]

The Dryer (and/ or oven) outlet are wired for a 3 prong cord, for added safety newer homes have been wired with outlets that use a 4 prong plug. If your appliance cord does not match the outlet, have a qualified appliance repairman install the correct cord.


Yea, but the ground plug is faced down on the 3 prong cord. :p

[Tom Edwards]

This question is along the same thread, I think.
Is there any need to replace one 4-prong cord (outlet has 4 vertical blades with one round prong) for a dryer if the GE dryer, newly purchased by a client, requires a 4-prong cord that has 3 vertical blades with 1 L-shaped prong. The property was built in 1998 and is a condo within a building with 12 separate units. Apparently, the electrical contractor used the 3 blade and one round prong outlet throughout and my client is being told by a GE appliance tech that the outlet must be converted to match the cord supplied by the manufacturer. There is some question as to whether the installed outlet is intended for a range/oven appliance instead of a dryer.
Is there a difference in the amperage rating between an oven and dryer that requires the different outlet/plug configuration for recognition?
I have not found any reference to outlet prongs for appliance cording. The closest reference I have found in the IRC is Table 3809.2 regarding maximum loads per conductor size. Any help is appreciated.

[Jerry Peck]

Tom,

It is best to NOT post duplicate threads, that the best that spreads answers out between threads, at the worst they don't get answered.

Here is the answer ... at your OTHER post: http://www.inspectionnews.net/home_inspection/electrical-systems-home-inspection-commercial-inspection/13379-3-wire-dryer-circuit.html