Electric Dryer Compliance

[RFEngineer]

I have searched the NEC regarding new installation electric dryer requirements pertaining to receptacles and branch circuits. I have seen numerous references to the effect that the post-1996 NEC now requires 4-wire service for electric dryer feeds. However, I see no direct reference in my 2008 edition of the NEC. I am familiar with Article 250.140, but what I need an exact reference stating the 4-wire requirement. Can anyone cite the exact source? Thanks.

 

[roger]

I don't understand the question. If the dryer is rated as 120/240 v and 250.140 requires the frame to be connected to an EGC, a four wire branch circuit is a must, how else could you get by with out one of the four neccessary conductors?

Roger

 

[nhfire77]

The OP did not specifically state the branch circuit was being replaced. Just that there is a new dryer installation. I won't assume but, if they are just replacing the dryer, and it's a 3 wire circuit, yo don't have to upgrade to a 4 wire.

Of course, if it is a new circuit then, you would need the 4 wire, like you said.

 

[jwjrw]

The OP did not specifically state the branch circuit was being replaced. I won't assume but, if they are just replacing the dryer, and it's a 3 wire circuit, yo don't have to upgrade to a 4 wire.

Of course, if it is a new circuit then, you would need the 4 wire, like you said.

You can even move it here to another location (as long as you dont extend it)
without going to a 4wire.

 

[roger]

The OP did not specifically state the branch circuit was being replaced. Just that there is a new dryer installation. I won't assume but, if they are just replacing the dryer, and it's a 3 wire circuit, yo don't have to upgrade to a 4 wire.

Of course, if it is a new circuit then, you would need the 4 wire, like you said.

The OP did say he is was familiar with article 250.140 which the exception explains the use of a three wire cicuit in existing installations.

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 connected 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

 

[RFEngineer]

The OP did not specifically state the branch circuit was being replaced. Just that there is a new dryer installation. I won't assume but, if they are just replacing the dryer, and it's a 3 wire circuit, yo don't have to upgrade to a 4 wire.

Of course, if it is a new circuit then, you would need the 4 wire, like you said.

Correct. I am only referring to new construction. I need the NEC Article citation that states a household electric dryer's receptacle and serving branch circuit must now be 4-wire for new installations.

Presumably, this was added to the NEC in 1996. However, I see nothing in the NEC that precludes (notwithstanding local code) installation of a 3-wire 240VAC circuit (L1-L2-G) and receptacle as part of new construction if a homeowner wanted to only use a 3-wire 240VAC dryer where a neutral is NOT utilized, nor is a neutral part of the dryer's design and operation. For example, a dryer that uses only 240VAC and ground but no neutral (L1-L2-G).

From my read, such a 3-wire dryer circuit under those circumstances where a neutral is not utilized by the dryer, is allowed under the NEC.

 

[roger]

Correct. I am only referring to new construction. I need the NEC Article citation that states a household electric dryer's receptacle and serving branch circuit must now be 4-wire for new installations.

There is no article that directly states that.

Presumably, this was added to the NEC in 1996. However, I see nothing in the NEC that precludes (notwithstanding local code) installation of a 3-wire 240VAC circuit (L1-L2-G) and receptacle as part of new construction if a homeowner wanted to only use a 3-wire 240VAC dryer where a neutral is NOT utilized, nor is a neutral part of the dryer's design and operation. For example, a dryer that uses only 240VAC and ground but no neutral (L1-L2-G).

If you can find a straight 240 volt residential dryer there would be no where to land a neutral anyways so a two wire circuit with an EGC would be fine

From my read, such a 3-wire dryer circuit under those circumstances where a neutral is not utilized by the dryer, is allowed under the NEC.

Absolutely, but finding the dyer may be a little difficult.

Roger

 

[GeorgeB]

From my read, such a 3-wire dryer circuit under those circumstances where a neutral is not utilized by the dryer, is allowed under the NEC.

Where there is no 120V load, AFAIUI, you are correct. I'm curious though; what manufacturer/model is being installed that does not run the light, timer and usually motor from 120?

To me, this may be a hole in the NEC. Say that is being put in, then the 2W+G circuit is installed. A replacement may have a 3 wire cord.

 

[RFEngineer]

Where there is no 120V load, AFAIUI, you are correct. I'm curious though; what manufacturer/model is being installed that does not run the light, timer and usually motor from 120?

Some newer Samsung and LG 240VAC models imported from EU and Asia that do not require a neutral.

Frankly, utilizing a 120VAC circuit path in any of today's appliances that otherwise require 240VAC to operate (e.g., heating elements) is an unnecessary and sloppy engineering practice when transformation from 240VAC to 120VAC can be cost-effectively accomplished to feed electronic timer or CPU circuits internal to the appliance. Designing appliances so that they do not require a neutral is quite easy -- and safe. I'm not sure why North American product manufacturers are still hung-up on having to operate from dual 240/120VAC circuits. The L1-L2-G branch distribution can work just fine if the appliance is designed to operate that way.

 

[iwire]

Designing appliances so that they do not require a neutral is quite easy -- and safe. I'm not sure why North American product manufacturers are still hung-up on having to operate from dual 240/120VAC circuits. The L1-L2-G branch distribution can work just fine if the appliance is designed to operate that way.

Actually it is smart engineering to have the dryer motor connected to 120 as dwelling units in the US may have a 208 or 240 volt supply and the unit has to work with either voltage.

A motor designed for 240 is not typically designed to also run on 208.

 

[GeorgeB]

A motor designed for 240 is not typically designed to also run on 208.

I'm CERTAINLY not trying to start a war here, but "most" residential air conditioning condensers and heat pumps are marked as being ok to do that ... is 240 better? Yes, I'd think so, with the lower current and same windings.

 

[iwire]

I'm CERTAINLY not trying to start a war here, but "most" residential air conditioning condensers and heat pumps are marked as being ok to do that ... is 240 better? Yes, I'd think so, with the lower current and same windings.

That is a good point.

 

[RFEngineer]

Actually it is smart engineering to have the dryer motor connected to 120 as dwelling units in the US may have a 208 or 240 volt supply and the unit has to work with either voltage.

A motor designed for 240 is not typically designed to also run on 208.

That's easily accomplished with a tapped motor winding brought out to the dryer's service connection. A screw-down wire tap is is then set between one of two positions (240 or 208VAC) at the time of installation.

 

[iwire]

That's easily accomplished with a tapped motor winding brought out to the dryer's service connection. A screw-down wire tap is is then set between one of two positions (240 or 208VAC) at the time of installation.

Yeah, appliance guys cannot get the ground connections right expecting them to deal with voltage taps would be foolish.:grin:

Chalk it up to tradition, or the fact they want it to work with the same receptacle that the older units worked with, I don't know.

But as a proud American I say phooey to change.

 

[roger]

I'm curious as to what listing these imports carry.

Roger

 

[RFEngineer]

Yeah, appliance guys cannot get the ground connections right expecting them to deal with voltage taps would be foolish.:grin:

Chalk it up to tradition, or the fact they want it to work with the same receptacle that the older units worked with, I don't know.

But as a proud American I say phooey to change.

From the factory and shipped to North America, the default would be 240VAC since few residential dryers in North America operate on 208VAC.

Another consideration is that the days of 60 Hz motor windings are numbered. My own clothes washer and dryer rely switch-mode power supplies that up-convert 60 Hz into a frequency of ~ 80 kHz. Manufacturing switch-mode power supplies and compatible motors is now less costly than comparable "big iron" transformers and motors. That's another argument against future use of a neutral conductor when an appliance otherwise requires 240VAC. super-efficient stepper motors that work on switched technology are also replacing big iron components.

 

[Jim W in Tampa]

Not digging in nec to find it but do recall seeing it say 4 wire outlet required.