NEC Questions and Answers – BASED ON THE 2011NEC
November 2010 – Part 2 of 2
By Mike Holt for EC&M Magazine
Here’s the follow up to yesterday’s newsletter. This includes all of the answers to the questions sent yesterday so you can see how you did.
Q11 Is an equipment grounding conductor allowed to serve dual duty as a grounding electrode conductor?
A11 No. An equipment grounding conductor isn’t permitted to be used as a grounding electrode conductor [250,121].
Q12 Is there any Code requirement for a raceway that crosses a structural expansion joint?
A12 Yes. A listed expansion/deflection fitting or other approved means must be used where a raceway crosses a structural joint intended for expansion, contraction or deflection [300.4(H)].
Q13 Does the Code allow the use of ceiling-support wires to support raceways and cables?
A13 No. Raceways, cable assemblies, boxes, cabinets, and fittings must be securely fastened in place. The ceiling-support wires or ceiling grid must not be used to support raceways and cables (power, signaling, or communications). However, independent support wires that are secured at both ends and provide secure support are permitted [300.11(A)]. Figure 300–10
(1) Fire-Rated Ceiling Assembly. Electrical wiring within the cavity of a fire-rated floor-ceiling or roof-ceiling assembly can be supported by independent support wires attached to the ceiling assembly. The independent support wires must be distinguishable from the suspended-ceiling support wires by color, tagging, or other effective means.
(2) Nonfire-Rated Ceiling Assembly. Wiring in a nonfire-rated floor-ceiling or roof-ceiling assembly can be supported by independent support wires attached to the ceiling assembly. The independent support wires must be distinguishable from the suspended-ceiling support wires by color, tagging, or other effective means. Figure 300–11
Q14 What wiring methods are allowed in ducts and other spaces used for environmental air handling?
A14 Section 300.22 addresses this question. The provisions of this section apply to the installation and uses of electrical wiring and equipment in ducts used for dust, loose stock, or vapor removal; ducts specifically fabricated for environmental air, and spaces used for environmental air (plenums).
(A) Ducts Used for Dust, Loose Stock, or Vapor. Ducts that transport dust, loose stock, or vapors must not have any wiring method installed within them. Figure 300–13
(B) Ducts Specifically Fabricated for Environmental Air. If necessary for direct action upon, or sensing of, the contained air, Type MC cable that has a smooth or corrugated impervious metal sheath without an overall nonmetallic covering, electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, or rigid metal conduit without an overall nonmetallic covering can be installed in ducts specifically fabricated to transport environmental air. Flexible metal conduit in lengths not exceeding 4 ft can be used to connect physically adjustable equipment and devices within the fabricated duct.
Equipment is only permitted within the duct specifically fabricated to transport environmental air if necessary for the direct action upon, or sensing of, the contained air. Equipment, devices, and/or illumination are only permitted to be installed in the duct if necessary to facilitate maintenance and repair. Figure 300–14
(C) Other Spaces Used for Environmental Air (Plenums). This section applies to wiring and equipment in spaces not specifically fabricated for environmental air-handling purposes (plenums) but used for air-handling purposes as a plenum. This requirement doesn’t apply to habitable rooms or areas of buildings, the prime purpose of which isn’t air handling.
Note 1: The spaces above a suspended ceiling or below a raised floor used for environmental air are examples of the type of space to which this section applies. Figure 300–15
Note 2: The phrase “other space used for environmental air (plenum) ” correlates with the term “plenum” in NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems, and other mechanical codes where the plenum is used for return air purposes, as well as some other air-handling spaces.
(1) Wiring Methods. Electrical metallic tubing, rigid metal conduit, intermediate metal conduit, armored cable, metal-clad cable without a nonmetallic cover, and flexible metal conduit can be installed in environmental air spaces. If accessible, surface metal raceways or metal wireways with metal covers can be installed in environmental air spaces. Figure 300–16
(2) Cable Tray Systems.
(a) Metal Cable Tray Systems. Metal cable tray systems can be installed to support the wiring methods and equipment permitted by this section. Figure 300–19
(3) Equipment. Electrical equipment with a metal enclosure or nonmetallic enclosures listed for use within an air-handling space (plenum) and having adequate fire-resistant and low-smoke-producing characteristics can be installed.
Q15 When can power distribution blocks be installed in junction boxes?
A15 Power distribution blocks installed in junction boxes over 100 cu in. must comply with the following [314.28(E)]: Figure 314–12
(1) Installation. Be listed as a power distribution block.
(2) Size. Be installed in a box not smaller than required by the installation instructions of the power distribution block.
(3) Wire-Bending Space. The junction box is sized so that the wire-bending space requirements of 312.6 can be met.
(4) Live Parts. Exposed live parts on the power distribution block aren’t present when the junction box cover is removed.
(5) Through Conductors. Where the junction box has conductors that don’t terminate on the power distribution block(s), the through conductors must be arranged so the power distribution block terminals are unobstructed following installation.
Q16 When is the neutral conductor required to be provided at the switch location for lighting loads?
A16 Switches controlling line-to-neutral lighting loads must have a neutral provided at the switch location [404.2(C)] unless either of the conditions of the following exception are met.
Ex: The neutral conductor isn’t required at the switch location if:
(1) The conductors for switches enter the device box through a raceway that has sufficient cross-sectional area to accommodate a neutral conductor. Figure 404–1
(2) Cable assemblies for switches enter the box through a framing cavity that’s open at the top or bottom on the same floor level, or through a wall, floor, or ceiling that’s unfinished on one side. Figure 404–2
Note: The purpose of the neutral conductor is to complete a circuit path for electronic lighting control devices.
Q17 What does the NEC require when replacing receptacles in locations that now require arc fault circuit interrupter (AFCI) protection?
A17 Effective January 1, 2014, where a receptacle outlet is supplied by a branch circuit that requires arc-fault circuit-interrupter protection [210.12(A)], a replacement receptacle at this outlet must be one of the following [406.4(D)(4)]:
(1) A listed (receptacle) outlet branch-circuit type arc-fault circuit-interrupter receptacle.
(2) A receptacle protected by a listed (receptacle) outlet branch-circuit type arc-fault circuit-interrupter type receptacle.
(3) A receptacle protected by a listed combination type arc-fault circuit interrupter type circuit breaker.
Q18 What does the NEC require when replacing receptacles in locations that now require tamper-resistant receptacles?
A18 Listed tamper-resistant receptacles must be provided where replacements are made at receptacle outlets that are required to be tamper resistant elsewhere in this Code [406.4(D)(5)]:.
Q19 What does the NEC require when replacing receptacles in locations that now require weather-resistant receptacles?
A19 Weather-resistant receptacles must be provided where replacements are made at receptacle outlets that are required to be so protected elsewhere in the Code. [406.4(D)(6)]:
Q20 Where are tamper-resistant receptacles required by the Code?
A20 All nonlocking type 15A and 20A, 125V receptacles in the following areas of a dwelling unit [210.52] must be listed as tamper resistant [406.12].
• Wall Space—210.52(A)
• Small-Appliance Circuit—210.52(B)
• Countertop Space—210.52(C)
• Bathroom Area—210.52(D)
• Outdoors—210.52(E)
• Laundry Area—210.52(F)
• Garage and Outbuildings—210.52(G)
• Hallways—210.52(H)
Ex: Receptacles in the following locations aren’t required to be tamper-resistant:
(1) Receptacles located more than 5½ ft above the floor.
(2) Receptacles that are part of a luminaire or appliance.
(3) A receptacle located within dedicated space for an appliance that in normal use isn’t easily moved from one place to another.
(4) Nongrounding receptacles used for replacements as permitted in 406.4(D)(2)(a).
