NEC reference for clothes dryer outlet requirement

[Hank S]

Hello Codeman.

I'm thumbing through my 2008 NEC looking for the code reference requiring the 4-wire/4-blade configuration for 220V clothes dryer receptacles. Can you point me in the right direction?

[Jerry Peck - Codeman]

Hi Hank,

You have not been able to find a requirement for a 240 volt dryer receptacle as there is none, however, when a 240 volt clothes dryer receptacle is installed, that receptacle outlet would be required to be a 4-wire receptacle.

Let's use a house with gas clothes dryer as example - why would a 240 volt clothes dryer receptacle be necessary?

What if the house had gas for a gas clothes dryer, but an owner/occupant decided to use an electric clothes dryer instead? That owner/occupant would need to have a 240 volt 4-wire receptacle installed at their expense. Yes, that is going to cost a lot ... A LOT ... more than if that receptacle was installed at the time of construction, but ... you must remember that all codes are "minimum" standards, codes *are not* "good", "better", or "best" practices.

[Hank S]

Thanks Jerry. No, I was not questioning the requirement for the outlet, just when there is one, what the code reference for 4-wires is. I think I stumbled across it the other night while the book was out, discussing the need for a separate neutral & grounding wire.

[Jerry Peck - Codeman]

Hi Hank,

I was not questioning the requirement for the outlet, just when there is one, what the code reference for 4-wires is.

My apologies, I did completely misunderstand your question.

What you are referring to is that older installations of ranges and clothes dryers were allowed to use the grounded conductor as the ground and did not require a grounding conductor.

The 1996 NEC was the last edition which allowed those installation:
- 250-60. Frames of Ranges and Clothes Dryers.
- - This section shall apply to existing branch-circuit installations only. New branch-circuit installations shall comply with Sections 250-57 and 250-59. 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 grounded in the manner specified by Section 250-57 or 250-59; or, except for mobile homes and recreational vehicles, shall be permitted to be grounded to the grounded circuit conductor if all of the conditions indicated in (a) through (d) below are met.
- - - (a) 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.
- - - (b) The grounded conductor is not smaller than No. 10 copper or No. 8 aluminum.
- - - (c) 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.
- - - (d) Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.

The 1999 NEC edition no longer allowed those installation with new installation, those installations were allowed to remain under an exception for "existing installations".

The current 2011 NEC edition:
- 250.140 Frames of Ranges and Clothes Dryers.
- - 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 connected to the equipment grounding conductor in the manner specified by 250.134 or 250.138.
- - - 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.

My apologies for not understanding the question correctly at first - the above should be what you are looking for.