I've been asked to connect a newer 4 wire clothes dryer with a 120v motor to a older 3 wire 30 amp 240 volt branch circuit I've done it many times and didn't think much about until now. I'm sure its a old topic for this forum, however with a reasonable search I could not find any related post in regard to a dryer having a 120 volt motor. The customers appliance repairman tells me the dryer has a 120 volt motor and a 240 volt heating element. Is it a liability and/or code violation to connect a 3 wire cords to these type dryers and tie the dryers neutral and equip. ground together at the dryer? I was not aware that these newer dryers had a 120 volt motor. I just thought it was only the timer that was 120 volt, so now I'm concerned about this additional current on the equipment ground......Na?ve here, but wanting to do it right.....Thanks in advance for your insight and comments
4 wire Dryer with 120 volt motor on 3 wire circuit is it a liability to connect ?
- Thread starter Mule
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texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
Not a problem. All household clothes dryers are listed to work with a 4 wire or 3 wire cord. If you use a 3 wire cord just make sure you have the factory supplied bonding jumper installed. If there is a more recent 4 wire dryer recep. you just make sure the bonding jumper is not installed.
But this begs a question, why do they need an electrician for this if the recep. is already installed? The instructions should make this clear on how to handle this based on the type of the available recep. The 120 volt motor you mention has always been there.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The presence of a 120 volt motor just requires that you have a neutral wire, and by itself has no effect on the requirement for a separate EGC wire, which is the Code concern.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
a bare Neutral wire insulated by a type NM sheath ?
Used to be allowed at one time, AFAIK.
The wire in the attachment cord needs to be insulated though.
I see your point that perhaps in the original wire was just a ground and no neutral was ever provided or needed. But the receptacle cannot tell the difference.
Depends on where the other end of the wire lands, if it is at a panel with separate ground and neutral bars.
Well that's the other part of this service call I'm going on tomorrow that I didn't mention. The Appliance repairman tells me he was getting unbalanced voltages when measuring A-phase to ground and B-phase to ground. He goes to the panel and moves and re-lands the dryer branch circuit EG from the ground bus to the neutral bus in the panel. He says when he did that the voltages were then balanced. I told him it sounds like a bonding issue because something is floating.......I haven't seen it but I'm going out there tomorrow
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
If this was a subpanel, then the two bars should not be connected except through the feeder EGC and neutral to the main and that may be incorrect.
If he was looking at the main panel, then absolutely some bond is missing. But there would not necessarily be two separate bars at a service disconnect main panel in the first place.
Definitely a good idea to look at it all yourself and assume nothing.
PS: If the original installation did connect the bare wire as ground and not a neutral, then re-purposing it as a current carrying neutral may well defeat the grandfathering that allows a combined ground and neutral in the first place. A gray area for me.
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Yeah, I asked him if it was the main panel or sub panel, and he said main panel with separate buses. Yeah, I agree that most of the electrical world is bonding twice, once in POCO's meter socket and then a second time at the panelboard bus.......which is incorrect to me, but widely done.....TWO BULLS EYES :blink:
kwired
Electron manager
- Location
- NE Nebraska
a bare Neutral wire insulated by a type NM sheath ?
I don't go back far enough to know for certain, but AFAIK only time a bare neutral conductor was allowed was if it were part of a type SE cable assembly. Regular 10-2 with ground NM cable was not code compliant for this use, I have seen it done but doesn't mean it was right.
As far as the 120 volt motor - I do not recall ever seeing a household type clothes dryer that did not have a 120 volt motor. I don't regularly do repair work on these but all the ones I ever did dig into were 120 volt motor. Timer and any other controls were also 120 volt, only 240 volt load I have ever seen is the heating element. Lose the proper line and the thing still runs - just with no heat.
Technically you are right but not a real problem if the service grounded circuit conductor is bonded twice once in the meter socket and another in the Main Panel. What matters is the grounded circuit conductor is not bonded again after the main panel.
AdrianWint
Senior Member
- Location
- Midlands, UK
I'm from the UK and I read this topic with a .... fascination!
If I understand the topic correctly you are removing the 4 core lead (L1, L2, N & E ?) & reconnecting a 3 core lead (L1, L2 & E ?) by connecting together the neutral & ground in the dryer so that a current will deliberately flow along the ground wire since there is no neutral available?
I understand why this will work (and that you common the neutral & ground at the service entrance) but for me it seems so .... strange.... our wiring regulations absolutely forbid the use of an egc as a 'normal' current carrying conductor under any circumstances.......
or have I mis-understood?
(I'm not questioning the rules - the rules are different Country by Country... just merely trying to increase my knowledge of electrical system in other parts of the world)
If I understand the topic correctly you are removing the 4 core lead (L1, L2, N & E ?) & reconnecting a 3 core lead (L1, L2 & E ?) by connecting together the neutral & ground in the dryer so that a current will deliberately flow along the ground wire since there is no neutral available?
I understand why this will work (and that you common the neutral & ground at the service entrance) but for me it seems so .... strange.... our wiring regulations absolutely forbid the use of an egc as a 'normal' current carrying conductor under any circumstances.......
or have I mis-understood?
(I'm not questioning the rules - the rules are different Country by Country... just merely trying to increase my knowledge of electrical system in other parts of the world)
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
A valid question, and without the historical background it is quite understandable.
The premise is not replacing an existing four wire cord with a three wire cord, but rather that fact that at one time it was permitted by NEC to run only a three wire branch circuit wire set for a large appliance like a cooking range or a clothes dryer. This was at the same period that there was no requirement to bring a ground to a normal light or appliance circuit at all.
For the most part loads did not have any grounding of exposed metal parts, but it was considered OK in the case of range or dryer to connect the case to the neutral wire. Both range and dryer would typically have at least one line to neutral load (timer motor, lamp, etc.) in addition to the line-to-line loads, so the neutral would be current carrying. If the dryer motor was 120V or the range elements used a 120 volt connection for low power, the neutral could carry significant current.
The receptacle plug contains only three contacts.
The NEC allows use of a combined neutral/ground wire in the appliance cord for legacy applications where there are only three conductors in the wall.
What is causing concern in this particular case is that the third wire in the wall is uninsulated (except for the overall sheath), and was landed at the ground bus rather than at the neutral bus of the panel. And there appears to be a problem with the overall ground to neutral bonding to complicate things.
New installations are governed by the same restriction that you cite, namely that the Equipment Grounding Conductor (EGC) not be used to carry normal current.
The only exception there at the moment is for presence detectors or dimming controls in light switches where there is only a switch loop and no neutral at the device box. Which is another can of worms....
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JDBrown
Senior Member
- Location
- California
- Occupation
- Electrical Engineer
Somebody will surely correct me if I'm wrong, but it's my understanding that it was never permitted to use an EGC as a neutral conductor, but that it was permitted to use a neutral conductor as an EGC. It may be a subtle distinction, but I think it's the cause of a lot of the concern in this case -- the uninsulated conductor in 10-2 NM cable is an EGC, not a neutral.
kwired
Electron manager
- Location
- NE Nebraska
Instead of correcting you I will reaffirm what you said. To be technically correct it was permitted to use the grounded conductor for equipment grounding on ranges and clothes dryers, but was not permitted to use an equipment grounding conductor for carrying normal operating current of a circuit. This rule was simpler when the circuit originated at service equipment, or a feeder that supplied a separate building or structure that previously did not require a separate equipment grounding conductor, but becomes more complex when supplied by a feeder with separate grounded and equipment grounding conductors.
- Location
- Massachusetts
Most have 120 volt motor, lights and controls. Don't worry about it.
By the way, they are allowing the neutral to ground the dryer, they are not allowing an Equipment Grounding Conductor to carry current.
Rick Christopherson
Senior Member
A very common misconception with this topic is that the Ground is serving as the Neutral, when in fact, it is the reverse. It is the Neutral that is also serving as the chassis ground. If the scenario was the former, then a dryer receptacle would use a NEMA 6-30. Because it is the latter, the receptacle needs to be a NEMA 10-30.
Interesting point, It's the first time that I have had that pointed out.
Thanks
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
This is more than just word games because, among other things, there are rules that allow you to reduce the size of the neutral relative to the phase wires, but you cannot generally do that to the EGC.
Before you go any further, you need to double check the gauge of the "ground" wire in the branch circuit.
Rick Christopherson
Senior Member
I don't know why, but this posting was not visible to me when I made my posting below it. If I had seen it, I would have acknowledged it as preceding my own.
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