NEC Questions Based on the 2008 NEC Code

April Part 2

 

Here is 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.

 

By Mike Holt, for EC&M Magazine

 

Q1. How far away can a meter be from the service disconnect?

A1. The NEC doesn’t have a minimum or maximum length for service conductors between meter equipment and service disconnect, so there are no distance requirements for the proximity of the meter to the service equipment. If the meter is located outside and the service equipment is located inside, the service disconnecting means must be placed at a readily accessible location nearest the point of service conductor entry [230.70(A)(1)].

 

Warning: Because service-entrance conductors don’t have short-circuit or ground-fault protection, their length must be limited when installed inside a building. Some local jurisdictions have a specific requirement as to the maximum length permitted within a building.

 

Q2. How many receptacles can be installed on a general-purpose branch circuit?

A2. The NEC doesn’t limit the number of GFCI-protected receptacle outlets on a general-purpose branch circuit in a dwelling unit [220.14(J)], but for other than dwelling units, the NEC limit is 13 receptacle outlets each at 180VA per mounting strap [220.14(I).

Circuit VA = Volts x Amperes

Circuit VA = 120V x 20A

Circuit VA = 2,400 VA

Number of Receptacles = 2,400 VA/180 VA

Number of Receptacles = 13

 

Q3. How many 12 AWG conductors can I install in a 1” EMT conduit?

A3. EMT must be large enough to permit the installation and removal of conductors without damaging the conductor insulation [358.22], and this is accomplished by complying with conductor fill limitations of Table 1 of Chapter 9. Since all of the conductors are the same size, Annex C, Table C.1 can be used to determine the number of conductors; twenty-six conductors.

 

Although the NEC permits twenty-six 12 THHN conductors in trade size 1 EMT, 310.15(B)(2)(a) requires the ampacity of the conductors to be adjusted when installing more than three current-carrying conductors in the raceway.

 

Q4. Can the lights in a dwelling unit bathroom be on the same circuit as the bathroom receptacles?

A4. According to 210.11(C)(3) 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. However, the exception to this rule allows a single 20A, 120V branch circuit to supply all outlets in a single bathroom, as long as no single load fastened in place is rated more than 10A [210.23(A)].

 

Q5. After driving two ground rods, we still can’t get the ground resistance to be 25 ohms or less. What do we do?

A5. The NEC does not require that you achieve a 25 ohm ground resistance if you have two ground rods, so just go home and call it a day. The rule is that when the grounding electrode system consists of a single ground rod having a contact resistance to the earth of over 25 ohms, it must be augmented with an additional electrode located not less than 6 ft away [250.56].

Q6. What are the NEC requirements when using Type MC or NM cable as the feed and switch-leg for a single-pole switch?

A6. The white conductor within the cable must be used to supply the power to the switch and it must be permanently reidentified at each location where the conductor is visible to indicate its use as an ungrounded conductor [200.7(C)(2)]. The black conductor is to be used as the switch leg to the luminaire.

 

Q7. What are the rules for terminating more than one conductor on a terminal??

A7. The general requirement is that all terminals are rated for the termination of only one conductor. Terminals suitable for more than one conductor must be identified for this purpose, either within the equipment instructions or on the terminal itself [110.14(A)]. Some circuit breakers which are rated 30A or less are listed for the termination of two conductors and this information is contained in the product instructions.

 

Q8. What are the GFCI protection requirements for 15A and 20A, 125V receptacles?

A8. GFCI protection is required for all 15A and 20A, 125V receptacles located in the following dwelling unit locations [210.8(A)]:

(1) Bathroom Area. GFCI protection is required for all 15A and 20A, 125V receptacles in the bathroom area of a dwelling unit.

(2) Garages and Accessory Buildings. GFCI protection is required for all 15A and 20A, 125V receptacles in garages, and in grade-level portions of accessory buildings used for storage or work areas of a dwelling unit.

(3) Outdoors. All 15A and 20A, 125V receptacles located outdoors of dwelling units, including receptacles installed under the eaves of roofs, must be GFCI protected.

Exception to (3): GFCI protection isn’t required for a fixed electric snow-melting or deicing equipment receptacle supplied by a dedicated branch circuit, if the receptacle isn’t readily accessible and the equipment or receptacle has ground-fault protection of equipment (GFPE) [426.28].

(4) Crawl Spaces. All 15A and 20A, 125V receptacles installed in crawl spaces at or below grade of a dwelling unit must be GFCI protected.

(5) Unfinished Basements. GFCI protection is required for all 15A and 20A, 125V receptacles located in the unfinished portion of a basement not intended as a habitable room and limited to storage and work areas.

Exception: A receptacle supplying only a permanently installed fire alarm or burglar alarm system is not required to be GFCI protected [760.41(B) and 760.121(B)].

(6) Kitchen Countertop Surfaces. GFCI protection is required for all 15A and 20A, 125V receptacles that serve countertop surfaces in a dwelling unit.

(7) Laundry, Utility, and Wet Bar Sinks. GFCI protection is required for all 15A and 20A, 125V receptacles located within an arc measurement of 6 ft from the sink.

(8) Boathouses. GFCI protection is required for all 15A and 20A, 125V receptacles located in a dwelling unit boathouse.

GFCI protection is required for all 15A and 20A, 125V receptacles installed in the following nondwelling locations:

(1) Bathrooms. All 15A and 20A, 125V receptacles installed in commercial or industrial bathrooms must be GFCI protected.

(2) Kitchens. All 15A and 20A, 125V receptacles installed in an area with a sink and permanent facilities for food preparation and cooking [Article 100], even those that don’t supply the countertop surface , must be GFCI protected.

(3) Rooftops. All 15A and 20A, 125V receptacles installed on rooftops must be GFCI protected.

(4) Outdoors. All 15A and 20A, 125V receptacles installed outdoors must be GFCI protected.

Exception No. 1 to (3) and (4): Exception: GFCI protection isn’t required for a fixed electric snow-melting or deicing equipment receptacle supplied by a dedicated branch circuit, if the receptacle isn’t readily accessible and the equipment or receptacle has ground-fault protection of equipment (GFPE) [426.28].

(5) Sinks. All 15A and 20A, 125V receptacles installed within 6 ft of the outside edge of a sink must be GFCI protected.

 

Additional GFCI protection requirements are contained in Article 590 for temporary wiring as well as Article 680 for pools, spas and hot tubs, fountains, and hydromassage bathtubs.

 

Q9. What are the separation requirements when installing signaling and communications cables in cable trays with Type MC and TC cables?

A9. None. However, if the power conductors are installed as individual conductors, then a separation of 2 in. or a barrier required, in accordance with:

Coaxial Cables, 820.133(A)(1)(b) Ex 1

Class 2 and 3 Cables, 725.136(B) and 725.136(I)

Communications Cables, 800.133(A)(2) Ex 1

Fire Alarm Cables, 760.136(G)

Optical Fiber Cables, 770.133(B)

Intrinsically Safe Systems Cables, 504.30(A)(2) Ex 1

Radio and Television Cables, 810.18(B) Ex 1

 

Q10. What are working space requirements for telecommunications equipment?

A10. The working space requirement for power equipment contained in 110.26(A) do not apply to communications equipment [90.3], however the telecommunications equipment cannot be located in the required workspace for power equipment

 

Q11. Can a receptacle for a LCD projector that is cord-and-plug-connected be located above a suspended ceiling?

A11. No, cords are not permitted to be run through holes in structural or suspended/dropped ceilings [400.8(2)] and they are also not allowed to be concealed by walls, floors, or ceilings, or located above suspended or dropped ceilings [400.8(5)].

 

Q12. What are the cable fill limitations when installing telecom cable in a raceway?

A12. Where communications cables are installed in a Chapter 3 raceway, the raceway must be installed in accordance with Chapter 3, except for the raceway fill requirements, which do not apply [800.110].