Multiwire Branch Circuits, Temporary Wiring and More

Article 110—Requirements for Electrical Installations; Article 210—Branch Circuits; Article 215—Feeders; Article 314—Outlet, Device, Pull, and Junction Boxes; Conduit Bodies; Fittings; and Handhole Enclosures; Article 334—Nonmetallic-Sheathed Cable: Types NM, NMC, and NMS; Article 517—Health Care Facilities; Article 590—Temporary Installation; Article 605—Office Furnishings (Consisting of Lighting Accessories and Wired partitions)

Multiwire branch circuits for office partitions

Does the National Electrical Code (NEC) permit multiwire branch circuits to supply freestanding office partitions? I would like to use three-phase, four-wire branch circuits, consisting of 3–12 AWG copper conductors with a 10 AWG neutral supplied from a 208Y/120 volt system. Are three-phase, single-pole circuit breakers acceptable? The wiring method is flexible metal conduit.

Fixed-type partitions and freestanding partitions are allowed to be connected to multiwire branch circuits where all ungrounded conductors of the branch circuit can be disconnected simultaneously from the panelboard where the branch circuit originates. This applies to partitions that are connected to the wiring system by one of the wiring methods recognized in Chapter 3. Freestanding partitions connected to the wiring system in the building through a cord-and-plug connection are not permitted to be supplied by multiwire branch circuits. These rules are in 605.6, 605.7 and 605.8.

Flexible metal conduit must contain an equipment-grounding conductor where the length is greater than 6 feet (see 348.60 and 250.118).

Temporary wiring

The local electrical inspector turned down temporary wiring for construction in a new store of Type III construction because he said NM cable could not be used where run as open (exposed) wiring. He said 334.10(3) does not permit Type NM cable. Is this a correct interpretation?

Type NM cable may be used to supply construction wiring in any building without regard to the construction type of the building. Although 334.10 and 334.12 restrict its use in Types III, IV and V construction, to use Type NM in a Type III building, the cable must be concealed within walls, floors or ceilings that provide a thermal barrier of material that has at least a 15-minute finish rating. However, temporary wiring for feeders and branch circuits is permitted to be exposed in any building construction type. This last sentence appears in both 590.4 (B) and (C): “Type NM and NMC cables shall be permitted to be used in any dwelling, building, or structure without any height limitation or limitation by building construction type and without concealment within walls, floors or ceilings.”

There is another part of Article 590, Temporary Installations, that gives the inspector additional authority to approve or reject the temporary wiring installation in 590.2(B), which reads, “Approval. Temporary wiring methods shall be acceptable only if approved based on the conditions of use and any special requirements of the temporary installation.”

The inspector may have seen some unsafe condition at the site during his inspection that caused him to reject the installation.

Loads on multiwire branch circuits

I have a commercial space with a three-phase 208Y/120-volt supply. Can I run an MC cable with 12 AWG copper conductors and four wires from a panelboard to a junction box to feed a 208-volt water heater using A- and B-phases, then use the neutral and C-phase to supply a luminaire (lighting fixture) in the same room? If the answer is yes, do I need handle ties on single-pole circuit breakers or may a three-pole circuit breaker be used? These are 15-ampere branch circuits.

The requirement in 210.4(C) permits line-to-neutral loads only on multiwire branch circuits, but Exception No. 2 permits line-to-line loads where the branch circuit overcurrent device opens all ungrounded conductors of the circuit simultaneously. A three-pole circuit breaker meets the requirement of this exception.

An equipment-grounding conductor must be part of the cable assembly. Either a five-wire cable is required, or the armor or armor and bond wire must be suitable for grounding the water heater and other parts of the branch circuit that must be grounded.

AFCIs in dwelling occupancies

Where are arc-fault circuit interrupters (AFCIs) required in residences?

A list of rooms and spaces that require combination type AFCIs appears in 210.12(B) and applies to 120-volt, single-phase 15- and 20-ampere branch circuits supplying outlets in family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, or similar rooms or areas.

AFCI protection is not required for power supplies to nonlimited fire alarm circuits and power-limited fire alarm circuits that meet the requirements of 760.41(B) and 760.121(B) where the branch circuits are installed in metal raceway or type AC cable and all outlet and junction boxes are metal.

Switches in hospital patient rooms

Does a wall switch for a luminaire in a patient bedroom have to be supplied by a metal raceway containing an insulated equipment-grounding conductor?

Part of 517.13(B) requires the metal raceway to contain an insulated copper equipment-grounding conductor for all electrical equipment operating at more than 100 volts and subject to personal contact. Metal cable assemblies that have armor that qualifies as a ground path also may be used where the cable contains an insulated-grounding conductor sized to comply with 250.122.

Marking of conductors

Is there a requirement in the NEC for marking of branch circuit conductors for a three-phase, four-wire circuit that originates from a 120/240-volt, three-phase, four-wire panelboard? This is a high-leg multiwire branch circuit with the neutral conductor as part of the branch circuit.

Yes, there are a few places where conductor identification is required. Section 110.15 requires high-leg marking: “On a 4-wire delta-connected system where the midpoint of one phase winding is grounded, only the conductor or busbar having the higher voltage to ground shall be durably and permanently marked by an outer finish that is orange in color or by other effective means.”

If another voltage system is present at the premises, 210.5(C) has this requirement: “Where the premises wiring system has branch circuits supplied from more than one nominal voltage system, each ungrounded conductor of a branch circuit shall be identified by phase or line and system at all termination, connection, and splice points.”

Section 215.12(C) has similar requirements for feeders where more than one nominal voltage system serves the premises. Another requirement for marking of the high-leg appears in 230.56 for service conductors.

Outdoor receptacles for ACs

Is an outdoor receptacle provided to service air conditioning equipment required to be protected by a ground-fault circuit interrupter? This receptacle is for the air conditioning of an office building and is located in a fenced area not accessible to the public.

Yes, 210.8(B) requires all 120-volt, single-phase, 15- and 20-ampere receptacles installed outdoors for other than dwelling units to be protected by a ground-fault circuit interrupter. This requirement is in 210.8(B)(5). A receptacle is required by 210.63, which reads: “Heating, Air--Conditioning, and Refrigeration Equipment Outlet. A 125-volt, single-phase, 15- or 20-ampere-rated receptacle outlet shall be installed at an accessible location for the servicing of heating, air-conditioning, and refrigeration equipment. The receptacle shall be located on the same level and within 7.5 m (25 feet) of the heating, air-conditioning, and refrigeration equipment. The receptacle outlet shall not be connected to the load side of the equipment disconnecting means.”

Supporting junction boxes

Does the National Electrical Code permit a 4-inch square box that contains only splices to be supported by electrical metallic tubing or is an independent means of support required?

An independent means of support is required. Section 314.23 provides methods of support for boxes and reads: “Supports. Enclosures within the scope of this article shall be supported in accordance with one or more of the provisions in 314.23(A) through (H).” Part (E) answers the question: “(E) Raceway Supported Enclosure, Without Devices, Luminaires or Lampholders. An enclosure that does not contain a device(s) other than splicing devices or support a luminaire(s), lampholder, or other equipment and is supported by entering raceways shall not exceed 1,650 cm3 (100 inches3) in size. It shall have threaded entries or have hubs identified for the purpose. It shall be supported by two or more conduits threaded wrench-tight into the enclosure or hub. Each conduit shall be secured within 900 mm (3 feet) of the enclosure or within 450 mm (18 inches) of the enclosure if all conduit entries are on the same side.” There is no permission to not secure boxes that are connected to electrical metallic tubing.

Dedicated space for a panelboard

Is it permissible to mount a panelboard on a wall that is 29 inches from a door that opens outward in front of the panelboard? With the door open, there is adequate working space in front of the panelboard. The voltage is 208Y/120 and the panelboard is 200 amperes.

Yes, the panelboard can be installed as indicated if the door is at least 30 inches wide and 6.5 feet tall, and the panelboard is centered on the wall to match the door opening.

The working space must provide at least 3 feet of clear space in front of the panelboard and a clear width of 30 inches with a height of not less than 6.5 feet. These minimum dimensions for the working space are in 110.26. If the open door extends into a passageway or open space, suitable guards must be provided when the door is open.

FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.

About the Author

George W. Flach

Code Q&A Columnist

George W. Flach was a regular contributing Code editor for Electrical Contractor magazine, serving for more than 40 years. His long-running column, Code Q&A, is one of the most widely read in the magazine's history. He is a former chief electrical...

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