NEC Questions and Answers based on 2008 NEC
July 2010
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, so you can see how you did.
Q1. What are the NEC requirements when replacing two-wire receptacles in bathrooms where there is no equipment grounding conductor in the outlet box?
A1. When existing receptacles are replaced in locations where GFCI protection is currently required, the replacement receptacles must be GFCI protected. This includes the replacement of receptacles in dwelling unit bathrooms, garages, outdoors, crawl spaces, unfinished basements, kitchen countertops, rooftops, or within 6 ft of laundry, utility, and wet bar sinks [406.4(D)(3)].
If no equipment grounding conductor exists in the outlet box for the receptacle, such as old 2-wire Type NM cable without an equipment grounding conductor, existing nongrounding-type receptacles can be replaced with [406.4(D)(2)]: Figure 406-04D2 01
- A GFCI-type receptacle marked “No Equipment Ground”, or
- A grounding-type receptacle, if GFCI protected and marked “GFCI Protected” and “No Equipment Ground.”
Author’s Comment: GFCI protection functions properly on a 2-wire circuit without an equipment grounding conductor because the circuit equipment grounding conductor serves no role in the operation of the GFCI-protection device. Figure 406-04D2 02
Q2. Is GFCI protection required for drinking water fountains?
A2. Yes, see 422.52. Figure 422–15
Q3. Is a hard-wired 120V rated electric heaters in a bathroom required to be GFCI protected?
A3. No, GFCI protection is only required for 15A and 20A, 125V receptacles located in the bathroom area of a dwelling unit [210.8(A)]. Figure 210–11
Q4. Since the utility power meter has the neutral bonded to the enclosure, is it necessary to install a main bonding jumper in the service disconnect?
A4. Yes, a service neutral conductor from the electric utility must be routed with the ungrounded conductors and terminate to the service disconnecting means via a main bonding jumper [250.24(B) and 250.28]. Figures 250-24C0 01 and 250-24C0 02
Author’s Comment: The service neutral conductor provides the effective ground-fault current path to the power supply to ensure that dangerous voltage from a ground fault will be quickly removed by opening the overcurrent device [250.4(A)(3) and 250.4(A)(5)]. Figure 250-24C0 03
Danger: Dangerous voltage from a ground fault won’t be removed from metal parts, metal piping, and structural steel if the service disconnecting means enclosure isn’t connected to the service neutral conductor. This is because the contact resistance of a grounding electrode to the earth is so great that insufficient fault current returns to the power supply if the earth is the only fault current return path to open the circuit overcurrent device. Figure 250-24C0 04
Q5. What are the installation requirements for installing nonconductive fiber optic cable in the same raceway with power conductors?
A5. Nonconductive optical fiber cables are permitted to occupy the same cable tray or raceway with conductors for electric light, power, and Class 1 circuits [770.133(A)]. Figure 770–17
Nonconductive optical fiber cables can’t occupy a cabinet, outlet box, panel, or similar enclosure housing the electrical terminations of an electric light, power, or Class 1 circuit.
Ex 1: Nonconductive optical fiber cables are permitted to occupy the same cabinet, outlet box, panel, or similar enclosure housing the electrical terminations of an electric light, power, or Class 1 circuit, if the nonconductive optical fiber cable is functionally associated with the electric light, power, or Class 1 circuit.
Q6. What are the grounding requirements for a separate building supplied with a feeder?
A6. For buildings or structures supplied by a feeder , each building/structure’s disconnect must be connected to an electrode of a type identified in 250.52 [250.32(A)]. Figure 250–83
Author’s Comments:
• The grounding of the building/structure disconnecting means to the earth is intended to help in limiting induced voltages on the metal parts from nearby lightning strikes [250.4(A)(1)].
• The Code prohibits the use of the earth to serve as an effective ground-fault current path [250.4(A)(5) and 250.4(B)(4)].
Ex: A grounding electrode isn’t required where the building/structure is served with a 2-wire, 3-wire, or 4-wire multiwire branch circuit. Figure 250–84
To quickly clear a ground fault and remove dangerous voltage from metal parts, the building/structure disconnecting means must be connected to the circuit equipment grounding conductor of a type described in 250.118. If the supply circuit equipment grounding conductor is of the wire type, it must be sized in accordance with 250.122, based on the rating of the overcurrent device [250.32(B)(1)]. Figure 250-32B1 01
Caution: To prevent dangerous objectionable neutral current from flowing onto metal parts [250.6(A)], the supply circuit neutral conductor isn’t permitted to be connected to the remote building/structure disconnecting means [250.142(B)]. Figure 250-32B1 02
Ex: The neutral conductor can serve as the ground-fault return path for the building/structure disconnecting means for existing installations in compliance with previous editions of the Code where there are no continuous metallic paths between buildings and structures, ground-fault protection of equipment isn’t installed on the supply side of the circuit, and the neutral conductor is sized no smaller than the larger of:
(1) The maximum unbalanced neutral load in accordance with 220.61.
(2) The minimum equipment grounding conductor size in accordance with 250.122.
Q7. What are the AFCI protection requirements for dwelling units?
A7. All 15A or 20A, 120V branch circuits in dwelling units supplying outlets in family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, or similar rooms or areas must be protected by a listed AFCI device of the combination type [210.12(A)]. Figure 210-12A0 01
Author’s Comment: The 120V circuit limitation means AFCI protection isn’t required for equipment rated 230V, such as a baseboard heater or room air conditioner. For more information, visit www.MikeHolt.com, click on the “Search” link, and search for “AFCI.”
Note 3: See 760.41(B) and 760.121(B) for power-supply requirements for fire alarm systems.
Author’s Comment: Smoke alarms connected to a 15A or 20A circuit of a dwelling unit must be AFCI protected if the smoke alarm is located in one of the areas specified In 210.12(B). The exemption from AFCI protection for the “fire alarm circuit” contained in 760.41(B) and 760.121(B) doesn’t apply to the single- or multiple-station smoke alarm circuit typically installed in dwelling unit bedroom areas. This is because a smoke alarm circuit isn’t a fire alarm circuit as defined in NFPA 72, National Fire Alarm Code. Unlike single- or multiple-station smoke alarms, fire alarm systems are managed by a fire alarm control panel. Figure 210-12A0 02 N3
Ex 1: AFCI protection can be of the branch circuit type located at the first outlet if the circuit conductors are installed in RMC, IMC, EMT, or Type MC or steel armored Type AC cable meeting the requirements of 250.118, and the AFCI device is contained in a metal outlet or junction box.
Ex 3: AFCI protection can be omitted for a branch-circuit to a fire alarm system in accordance with 760.41(B) and 760.121(B), if the circuit conductors are installed in RMC, IMC, EMT, or steel sheath Type AC cable that qualifies as an equipment grounding conductor in accordance with 250.118.
Q8. Is it always necessary to install equipment grounding conductors in each parallel feeder from a generator to the transfer switch?
A8. If circuit conductors are installed in parallel in separate raceways as permitted by 310.4, an equipment grounding conductor must be installed for each parallel conductor set, Figure 250-s122F0 01.
Where conductors are installed in parallel in the same raceway or cable tray, a single equipment grounding conductor is permitted [250.122(F)]. Figure 250-s122F0 02
Each equipment grounding conductor must be sized in accordance with Table 250.122, based on the rating of the circuit overcurrent device, but it’s not required to be larger than the circuit conductors [250.122(A)].
Q9. Is it acceptable to install a GFCI receptacle in a dwelling unit bathroom, and feed from the load side of the GFCI receptacle to a duplex receptacle in a second bathroom?
A9. Yes. One 20A, 120V branch circuit must be provided for the receptacle outlets required by 210.52(D) for a dwelling unit bathroom. This 20A bathroom receptacle circuit must not serve any other outlet, such as bathroom lighting outlets or receptacles in other rooms, but it can feed the receptacle outlets in multiple bathrooms, which can be fed on the load side of a GFCI receptacle from the first bathroom [210.8(A)(1) and 210.11(C)(3)]. Figure 210–32
Author’s Comment: A 15A, 125V receptacle is rated for 20A feed-through, so it can be used for this purpose [210.21(B)(3)].
Ex: A single 20A, 120V branch circuit is permitted to supply all of the outlets in a single bathroom, as long as no single load fastened in place is rated more than 10A [210.23(A)]. Figure 210–33
Question: Can a luminaire, ceiling fan, or bath fan be connected to the 20A, 120V branch circuit that supplies one bathroom?
Answer: Yes.
Q10. Can a receptacle outlet be installed above a suspended ceiling to feed cord-connected equipment such as a projector by feeding the cord through the ceiling?
A10. No, flexible cords must not be run through holes in walls, structural ceilings, suspended or dropped ceilings, or floors [400.8(2)]. Figure 400–5
Q11. Is the electrical wiring system used to feed ceiling fixtures allowed to be supported by the ceiling support wires?
A11. 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 300–33
Author’s Comment: Outlet boxes [314.23(D)] and luminaires can be secured to the suspended-ceiling grid if securely fastened to the ceiling-framing members by mechanical means such as bolts, screws, or rivets, or by the use of clips or other securing means identified for use with the type of ceiling-framing member(s) used [410.36(B)].
Q12. Are 20A rated duplex receptacles required when installed on a 20A, 120V branch circuit?
A12. No. If connected to a branch circuit that supplies two or more receptacles, receptacles must have an ampere rating in accordance with the values listed in Table 210.21(B)(3), which allows the use of either 15A or 20A rated receptacles on a 20A branch circuit. Figure 210–44
Table 210.21(B)(3) Receptacle Ratings |
Circuit Rating |
Receptacle Rating |
15A |
15A |
20A |
15A or 20A |
30A |
30A |
40A |
40A or 50A |
50A |
50A |
Q13. Does the Code requirement for bonding of pool water in Section 680.26(C) apply to above ground nonconductive pools?
A13 Yes, The requirement for bonding of pool water in Section 680.26(C) states that pool water must have an electrical connection to one or more of the bonded parts described in 680.26(B). If none of the bonded parts is in direct connection with the pool water, the pool water must be in direct contact with an approved corrosion-resistant conductive surface that exposes not less than 9 sq in. of surface area to the pool water at all times. The conductive surface should be located where it’s not exposed to physical damage or dislodgement during usual pool activities, and it must be bonded in accordance with 680.26(B).
