3-WIRE OR 4-WIRE?: Dryer and cooking unit circuits

Listen to this article

In past code cycles, changes were made to branch circuits that serve dryers and cooking units.

Some older rules effected dryer and range branch circuits, including air conditioning condensing units, where type SE cable with aluminum conductors was the preferred wiring method. All that can present challenges to electricians and service technicians that are unaware of the background of these circuits and may require different applications and remedies required while working on these types of existing circuits today.

The National Electric Code, before 1996, permitted the branch circuits that serve household dryers and ranges cooking units to use the grounded conductor (neutral) as both a neutral for the unbalanced loads for dryers and ranges but to also to be used as an equipment grounding conductor in certain applications some cases. There is still an exception in 250.140 that permits the neutral to be used as an equipment grounding conductor for these existing loads but only for existing installations and then only with certain restrictions.

The branch circuit must originate from the service equipment and not a sub-panel and the supply circuit must be 120/240, single-phase, 3-wire or 208Y/1120-volt derived from a 3-phase, 4-wire wye connected system. The grounded conductor for the equipment must be not smaller than a 10 AWG copper of 8 AWG aluminum. The grounded conductor must be insulated or can be uninsulated and part of an SE cable originating at the service. Last but certainly not least, the grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment. The existing branch circuit must comply with all of these requirements to remain as presently installed.

Type SE cable was often composed of used with copper or aluminum conductors and an uninsulated concentric neutral conductor. You may have seen a 30-amp or 50-amp, three-wire, 240-volt, receptacles that serve older dryer and range branch circuits. In 1996 the Code was revised, as is done it does every three years, to require a separate equipment grounding conductor with all these branch circuits, regardless of the supply where it is fed from. The older, existing, circuits require special attention when servicing or replacing the equipment and components.

The first issue is with new dryers and ranges. What do you do when the newer equipment is delivered to an older dwelling, with a four-wire flexible cord assembly from the factory or delivered with the new appliance and the dwelling only has an existing three-wire outlet? Short of a complete rewire of the branch circuit, the new equipment has a backwards compatible fix for existing circuits. The manufacturer will require the installer to connect the neutral terminal to the metallic frame of the equipment within the supply cord J-box in the back of the dryer or range.

You are not permitted to “bootleg” an equipment grounding conductor in the existing branch circuit outlet box. The exception is the existence of a qualifying EGC, such as a metal raceway or cable armor. But be aware that the 4-wire dryer receptacles will not fit in single gang boxes like the 3-wire does. Be careful and read every portion of the manufacturer’s instructions. Some appliances are not permitted to use the neutral for equipment grounding when installed in manufactured homes, mobile homes, or recreation vehicles with 4-wire electrical systems.

The next issue is the use of aluminum conductors which was common during this era. The NEC has permitted the use of aluminum conductors since 1901. It was first evaluated and listed for interior wiring by UL in 1946. It was really preferred for all residential branch circuits during the mid-1960’s until the late 1970’s due to high copper prices. If you are hardwiring equipment to these circuits with manufacturer supplied copper pigtails or tap conductors, make certain that you use the correct type of connections for aluminum to copper.

There is a right way and a very dangerous way to do this. Ideal Industries makes a purple “Wirenut” or wire connector that is listed for copper and aluminum splices only. It is for one time use and is not listed for aluminum-to-aluminum connections. It also requires installation following a manufacturer specified torque value. Another type of connection can be made using the “AlumiConn” connector by King Innovation. This can be used for both aluminum and copper conductors. However, both types of connectors are limited to size 10 AWG, maximum. Split-bolt connectors are another option if listed for copper to aluminum, however, remember to use an insulated encapsulating cover over the split bolt. After doing some research I have found only a few options that would comply with the Code and that would include mostly split-bolts or insulated Polaris® lugs for aluminum conductors larger than 10 AWG.

The Polaris lug catalog number, IT-4A, is rated for up to 4 AWG, copper, and aluminum, rated at 90⁰C. In addition, I could not find any manufacturer that permitted factory installed pigtails or taps to be connected directly to aluminum supply conductors without the use of listed connectors. The receptacle device used must also be listed for use with aluminum conductors. Most devices are listed for both and are often stamped AL-CU when it is listed for these applications.

Too many times I have seen or worked on equipment that was direct wired with copper to aluminum using nothing more than standard wire connectors and “Noalox” paste oozing out of them. “Noalox” is a brand of antioxidizing paste required for aluminum connections. It reminds me of the made-up, watertight, connector using silicon caulking squirted inside the “Wirenuts” and then wrapped with four layers of Scotch 33 electrical tape. The four layers electrical tape provides up to 1000-volts of insulation value: 250 volts per wrap. Just kidding, of course, but yes, I have seen and documented many of these connection methods hacks used by hacks or unqualified persons in the field. Another great example of why training and certification of electricians is so important.

The next issue is torque specifications. When terminating any type of conductor, you must follow the manufacturers specified torque values when installing conductors. Although it was an informational note prior to the 2017 NEC, it was always a requirement. In 110.3(B), the Code required us to following the manufacture’s installation instructions included in the listing or labeling. Then in the 2017 NEC, 110.14(D) specifically made it a mandatory requirement to follow the manufactures torque specifications which also requires us to have the proper tools to achieve the proper values at all conductor terminations. Electricians should have all the tools of the trade which should include torquing screwdrivers and torque wrenches of various sizes. Every termination should have this value specified as part of the listing instructions for us. Every device, every circuit breaker, every terminal bar, every mechanical lug will have this value specified. If not, you can use the values located in Annex I of the National Electric Code which provides recommended tightening torque values from UL standard 486-A and 486-B.

Lastly, in some newer installations that have adopted the 2020 NEC, 210.8 will require GFCI protection and 406.4(D)(3) requires the receptacle replacement to be brought up to the latest version of the code. If it now requires GFCI or AFCI protection, tamper resistant or weather resistant devices then you must make that type of replacement. Requirements for this section are not limited to voltage and amperage in most cases.

As you can see, when aluminum is used as a conductor, it requires specialized knowledge, tools, and equipment to not only prevent an electrical failure but also a potential electrical fire which could result in loss of property or life. Even while the newer aluminum alloy AA-8000 is proven to be as reliable as copper. It still falls back on workmanship and knowledge for the safe installation of this wiring method. Of course, this can apply applies to both copper and aluminum.

The following Code sections can be referenced to make sure the installation is compliant and essentially free from potential hazards with the latest adopted version of the Code in your area. These are from the 2017 and 2020 National Electric Code.

110.3(B), Installation and use
110.14, Electrical connections with dissimilar metals
110.14(D), Terminal connection Torque
210.8, GFCI Protection
406.4(D), Receptacle replacements.
250.114, Appliances that require equipment grounding conductors.
250.140, Frames of Dryers and Ranges to be grounded