2008 NEC Questions and Answers

NEC Questions & Answers Based on 2008 NEC
May 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 yesterday so you can see how you did.

Q1. What are the requirements when using a cord as a disconnect for appliances and motors?
A1. The requirements are found in 422.33(A) and (B).
(A) Attachment Plugs and Receptacles. A plug and receptacle can serve as the disconnecting means for a cord-and-plug-connected appliance.
(B) Cord-and-Plug-Connected Ranges. The plug and receptacle of a cord-and-plug-connected household electric range can serve as the range disconnecting means, if the plug is accessible from the front of the range by the removal of a drawer.

Q2. What are the conductor fill requirements for signaling circuits?
A2. The number and size of conductors or cables in a raceway are limited in accordance with 300.17. Raceways must be large enough to permit the installation and removal of conductors without damaging conductor insulation. [725.3(A)].

Same Size Conductors. When all conductors in a raceway are the same size and insulation, the number of conductors permitted can be found in Annex C for the raceway type.

Question: How many 18 TFFN fixture wires are permitted to be installed in trade size ½ electrical metallic tubing? Figure 725–6
(a) 22 (b) 26 (c) 30 (d) 40
Answer: (a) 22 conductors [Annex C, Table C.1]

Q3. What are the bonding requirements for service equipment enclosures?
A3. 250.92(A)(2) tells us that service equipment enclosures must be bonded, and 250.92(B)(1) tells us how to do it: Metal enclosures containing service conductors must be bonded together in accordance with 250.92(B) [250.92(A)(2)].

Comment: Metal raceways or metal enclosures containing feeder and branch-circuit conductors are required to be connected to the circuit equipment grounding conductor in accordance with 250.86.

Methods of Bonding. Metal enclosures containing service conductors must be bonded by bonding the metal parts to the service neutral conductor [250.92(B)(1)].

Comments:
• A main bonding jumper is required to bond the service disconnect to the service neutral conductor [250.24(B) and 250.28].
• At service equipment, the service neutral conductor provides the effective ground-fault current path to the power supply [250.24(C)]; therefore, an equipment grounding conductor isn’t required to be installed within PVC conduit containing service-entrance conductors [250.142(A)(1) and 352.60 Ex 2].

Q4. What are the bonding requirements for raceways containing service conductors?
A4. The requirements for raceways containing service conductors are found in 250.92(A) and (B):
Metal raceways containing service conductors must be bonded together in accordance with 250.92(B) [250.92(A)(1)].Comment: Metal raceways or metal enclosures containing feeder and branch-circuit conductors are required to be connected to the circuit equipment grounding conductor in accordance with 250.86.
250.92(B) Methods of Bonding. Metal raceways and metal enclosures containing service conductors must be bonded by one of the following methods:
(1) Neutral Conductor. By bonding the metal parts to the service neutral conductor. Figure 250–137

(2) Threaded Fittings or Entries. By using threaded couplings or threaded entries made up wrenchtight.
(3) Threadless Fittings. By using threadless raceway couplings and connectors made up tight.
(4) Bonding Fittings. When a metal service raceway terminates to an enclosure with a ringed knockout, a listed bonding wedge or bushing with a bonding jumper must be used to bond one end of the service raceway to the service neutral conductor. The bonding jumper used for this purpose must be sized in accordance with Table 250.66, based on the area of the service conductors within the raceway [250.92(B)(4) and 250.102(C)].

Comments:
• When a metal raceway containing service conductors terminates to an enclosure without a ringed knockout, a bonding-type locknut can be used.
• A bonding locknut differs from a standard locknut in that it has a bonding screw with a sharp point that drives into the metal enclosure to ensure a solid connection.
• Bonding one end of a service raceway to the service neutral provides the low-impedance fault current path to the source.

Q5. What are the conductor termination requirements for copper wire?
A5. The general rules for terminations are found in 110.14, and are highlighted as follows:
Conductor terminal and splicing devices must be identified for the conductor material and they must be properly installed and used.

Comments:
• See the definition of “Identified” in Article 100.
• Conductor terminations must comply with the manufacturer’s instructions as required by 110.3(B). For example, if the instructions for the device state “Suitable for 18-12 AWG Stranded,” then only stranded conductors can be used with the terminating device. If the instructions state “Suitable for 18-12 AWG Solid,” then only solid conductors are permitted, and if the instructions state “Suitable for 18-12 AWG,” then either solid or stranded conductors can be used with the terminating device.

FPN: Many terminations and equipment are marked with a tightening torque.

Comment: Conductors must terminate in devices that have been properly tightened in accordance with the manufacturer’s torque specifications included with equipment instructions. Failure to torque terminals can result in excessive heating of terminals or splicing devices (due to a loose connection), which can result in a fire because of a short circuit or ground fault. In addition, this is a violation of 110.3(B), which requires all equipment to be installed in accordance with listing or labeling instructions

110.14(A) Terminations. Conductor terminals must ensure a good connection without damaging the conductors and must be made by pressure connectors (including set screw type) or splices to flexible leads.

Comments:
• See the definition of “Connector, Pressure” in Article 100.
• Grounding conductors and bonding jumpers must be connected by listed pressure connectors, terminal bars, exothermic welding, or other listed means [250.8(A)].

One Wire Per Terminal. Terminals for more than one conductor must be identified for this purpose, either within the equipment instructions or on the terminal itself. Figure 110–23

Comments:
• Split-bolt connectors are commonly listed for only two conductors, although some are listed for three conductors. However, it’s a common industry practice to terminate as many conductors as possible within a split-bolt connector, even though this violates the NEC. Figure 110–24
• Many devices are listed for more than one conductor per terminal. For example, some circuit breakers rated 30A or less can have two conductors under each lug. Grounding and bonding terminals are also listed for more than one conductor under the terminal.

Split-bolt connectors for aluminum-to-aluminum or aluminum-to-copper conductors must be identified as suitable for the application.

Q6. What are the lighting and switch location requirements for dwelling units?
A6. There are more rules than many people think, and they are found in 210.70:
210.70(A) Dwelling Unit Lighting Outlets. Lighting outlets must be installed in:
(1) Habitable Rooms. At least one wall switch-controlled lighting outlet must be installed in every habitable room and bathroom of a dwelling unit.

Comment: See the definition of “Lighting Outlet” in Article 100.

Exception No. 1: In other than kitchens and bathrooms, a receptacle controlled by a wall switch can be used instead of a lighting outlet.

Exception No. 2: Lighting outlets can be controlled by occupancy sensors equipped with a manual override that permits the sensor to function as a wall switch.

Comment: The Code specifies the location of the wall switch-controlled lighting outlet, but it doesn’t specify the switch location. Naturally, you wouldn’t want to install a switch behind a door or other inconvenient location, but the NEC doesn’t require you to relocate the switch to suit the swing of the door. When in doubt as to the best location to place a light switch, consult the job plans or ask the customer.

(2) Other Areas.
(a) Hallways, Stairways and Garages. In dwelling units, not less than one wall switch-controlled lighting outlet must be installed in hallways, stairways, attached garages, and detached garages with electric power.
(b) Exterior Entrances. At least one wall switch-controlled lighting outlet must provide illumination on the exterior side of outdoor entrances or exits of dwelling units with grade-level access.

Comments:
• The NEC doesn’t require a switch adjacent to each outdoor entrance or exit. The Code considers switch location a “design issue” which is beyond the purpose of the NEC [90.1(C)]. For this reason, proposals to mandate switch locations have been rejected.
• A lighting outlet isn’t required to provide illumination on the exterior side of outdoor entrances or exits for a commercial or industrial occupancy.

(c) Stairway. Where the stairway between floor levels has six risers or more, a wall switch must be located at each floor level and at each landing level that includes an entryway to control the illumination for the stairway.

Exception to (a), (b), and (c): Lighting outlets for hallways, stairways, and outdoor entrances can be switched by a remote, central, or automatic control device.

(3) Storage and Equipment Rooms. At least one lighting outlet that contains a switch or is controlled by a wall switch must be installed in attics, underfloor spaces, utility rooms, and basements used for storage or containing equipment that requires servicing. The switch must be located at the usual point of entry to these spaces, and the lighting outlet must be located at or near the equipment that requires servicing.

(B) Guest Rooms or Guest Suites. At least one wall switch-controlled lighting outlet must be installed in every habitable room and bathroom of a guest room or guest suite of hotels, motels, and similar occupancies.

Exception No. 1: In other than bathrooms and kitchens, a receptacle controlled by a wall switch is permitted in lieu of lighting outlets.

Exception No. 2: Lighting outlets can be controlled by occupancy sensors equipped with a manual override that permits the sensor to function as a wall switch.

(C) Other Than Dwelling Units. At least one lighting outlet that contains a switch or is controlled by a wall switch must be installed in attics and underfloor spaces containing equipment that requires servicing. The switch must be located at the usual point of entry to these spaces, and the lighting outlet must be located at or near the equipment requiring servicing.

Comment: A 15A or 20A, 125V receptacle must be installed within 25 ft of HACR equipment [210.63].

Q7. What are the disconnecting means requirements for a water heater?
A7. For appliances rated over 300VA or 1/8 horsepower, a switch or circuit breaker located within sight from the appliance can serve as the appliance disconnecting means. If the switch or circuit breaker is capable of being locked in the open position, it doesn’t need to be within sight. The provision for locking or adding a lock to the disconnecting means must be on the switch or circuit breaker and remain in place with or without the lock installed. A portable locking means doesn’t meet the “locked in the open position” requirement [422.31(B)].

Comment: “Within Sight” is visible and not more than 50 ft from one to the other [Article 100].

Q8. When are hospital grade receptacles required?
A8. Not nearly as often as most people think. Only receptacles for inpatient sleeping beds or procedure table beds used in a critical care area (patient bed location) must be listed as “hospital grade" [517.18(B)].

Comment: “Hospital grade” receptacles aren’t required in treatment rooms of clinics, medical and dental offices, or outpatient facilities because these locations don’t have a “patient bed location” as defined in 517.2.

Q9. What are the requirements when installing 15A, 125V duplex receptacles on a 20A, 120V circuit?
A9. There are many rules, and they are found in 210.21(B), which covers receptacle ratings and loading:
(1) Single Receptacles. A single receptacle on an individual branch circuit must have an ampacity not less than the rating of the overcurrent device.
FPN: A single receptacle has only one contact device on its yoke [Article 100]. This means a duplex receptacle is considered two receptacles.
(2) Multiple Receptacle Loading. Where connected to a branch circuit that supplies two or more receptacles, the total cord-and-plug-connected load must not exceed 80 percent of the receptacle rating.

Comment: A duplex receptacle has two contact devices on the same yoke [Article 100]. This means even one duplex receptacle on a circuit makes that circuit a multioutlet branch circuit.

(3) Multiple Receptacle Rating. Where 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).

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

Q10. What receptacle outlets in a dwelling unit kitchen require GFCI protection and which don’t?
A10. GFCI protection is required for all 15A and 20A, 125V receptacles that serve countertop surfaces in a dwelling unit [210.8(A)(6)].
Comments:
• GFCI protection is required for all receptacles that serve countertop surfaces. But GFCI protection isn’t required for receptacles that serve built-in appliances, such as dishwashers or kitchen waste disposals.
• See 210.52(C) for the location requirements of countertop receptacles.

Q11. What are the GFCI requirements for receptacles in a commercial repair garage?
A11. GFCI protection is required for all 15A and 20A, 125V receptacles used for service and repair operations, such as electrical automotive diagnostic equipment, electric hand tools, portable lighting devices, etc 511.12].

Comment: See the definition of “Ground-Fault Circuit Interrupter” in Article 100.

Q12. What are the support requirements for EMT?
A12. Electrical metallic tubing must be installed as a complete system in accordance with 300.18 [300.10 and 300.12], and it must be securely fastened in place and supported in accordance with 358.30 (A) and (B), or unsupported as permitted in (C).
(A) Securely Fastened. Electrical metallic tubing must generally be securely fastened within 3 ft of every box, cabinet, or termination fitting, and at intervals not exceeding 10 ft. Figure 358–5

Comment: Fastening is required within 3 ft of termination, not within 3 ft of a coupling.

Exception No. 1: When structural members don’t permit the raceway to be secured within 3 ft of a box or termination fitting, an unbroken raceway can be secured within 5 ft of a box or termination fitting. Figure 358–6

(B) Horizontal Runs. Electrical metallic tubing installed horizontally in bored or punched holes in wood or metal framing members, or notches in wooden members, is considered supported, but the raceway must be secured within 3 ft of termination.
(C) Unsupported Raceways. Where oversized concentric or eccentric knockouts are not encountered, electrical metallic tubing is permitted to be unsupported between enclosures where the raceway is unbroken and not more than 18 in. in length. Figure 358–7

Q13. What are the grounding requirements for a generator mounted on a vehicle?
A13. The frame of a vehicle-mounted generator isn’t required to be grounded (connected to the earth) if [250.34(B)]:
(1) The generator frame is bonded to the vehicle frame,
(2) The generator only supplies equipment or receptacles mounted on the vehicle or generator, and
(3) The metal parts of the generator and the receptacle grounding terminal are connected to the generator frame.

Q14. What are the requirements when replacing two-wire receptacles?
A14. Where 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 in accordance with (a), (b), or (c) [406.3(D)(3)]:
(a) Another nongrounding-type receptacle.
(b) A GFCI-type receptacle marked “No Equipment Ground.”
(c) A grounding-type receptacle, if GFCI protected and marked “GFCI Protected” and “No Equipment Ground.”

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. See the definition of “Ground-Fault Circuit Interrupter” for more information.

Caution: The permission to replace nongrounding-type receptacles with GFCI-protected grounding-type receptacles doesn’t apply to new receptacle outlets that extend from an existing outlet box that is not connected to an equipment grounding conductor. Once you add a receptacle outlet (branch-circuit extension), the receptacle must be of the grounding type and it must have its grounding terminal connected to an equipment grounding conductor of a type recognized in 250.118, in accordance with 250.130(C).