All questions and answers are based on the 2005 NEC.
Q. What size conductor is required for a 25-hp, 208V, 3-phase fire pump motor (see Figure)?
A. Size conductors at 125% of the motor's full load current (FLC) as listed in Table 430.250. Per this table, the FLC of a 25-hp motor = 74.8A.
Conductor 5 74.8A × 1.25
Conductor 5 93.5A
A 3 AWG at 75°C is rated 100A
Note: The fire pump motor circuit protective device size must be set to carry the sum of the locked-rotor current of the fire pump motor indefinitely. According to Table 430.251(B), the locked-rotor current of a 25-hp, 208V, 3-phase motor is 404A.
Q. How far away must I place a receptacle outlet from a shower or bathtub?
A. The NEC does not require a receptacle to be located any given distance from a shower or bathtub. However, receptacles are not permitted to be installed within or directly over a bathtub or shower stall [406.8(C)].
Q. Can circuit breakers be installed in a bathroom?
A. Overcurrent protection devices, such as circuit breakers, must not be located in the bathrooms of dwelling units or guestrooms/guest suites of hotels or motels [240.24(E)], but they can be installed in commercial or industrial bathrooms. Be aware that a service disconnecting means is not permitted to be located in a bathroom, even in commercial or industrial facilities [230.70(A)(2)].
Q. What are the bonding requirements for a hydromassage tub motor if the water piping is nonmetallic?
A. All metal piping systems and grounded metal parts in contact with the circulating water must be bonded together using a solid copper bonding jumper no smaller than 8 AWG [680.74] to form an equipotential plane. If the water piping is plastic, this rule doesn't apply, and no bonding is required. Whether the piping is metallic or nonmetallic, the equipment grounding (bonding) conductor of the branch circuit feeding the hydromassage tub is providing the path for fault current.
Q. How far away must nonmetallic-sheathed cable (Romex) be placed from an air conditioning duct that is used to heat the home?
A. There is no clearance requirement for Type NM cable from a heating duct.
Q. Do I need to use hospital-grade receptacles in the treatment rooms of a chiropractor, medical, or dental examining room?
A. No. Hospital-grade receptacles are only required at “patient bed” locations [517.18] as defined in 517.2, which is “The location of an inpatient sleeping bed; or the bed or procedure table used in a critical patient care area.”
The treatment rooms of clinics, medical and dental, or outpatient facilities would not be considered a patient bed location, so hospital-grade receptacle are not required.
Caution: If the manufacturer of medical equipment requires that the equipment only be connected to a hospital-grade receptacle, then 110.3(B) requires the installation of hospital-grade receptacles in any clinic that uses this equipment.
Q. Can a dishwasher be hard-wired with NM, MC, or AC cable instead of having it cord and plug connected?
A. Yes. Per 422.16(B)(2), cords are permitted but not required.
Q. Is a flexible wiring method required for the connection of a dry-type transformer?
A. No. Typically in industrial settings, rigid metal conduit is used to protect the primary and secondary wiring.
Q. How do I size the circuit protection device for a fire pump motor?
A. The circuit protective device(s) must be selected or set to carry the sum of the locked-rotor current of the fire pump and pressure maintenance pump motor(s) indefinitely — and 100% of the ampere rating of the fire pump's accessory equipment. The requirement to carry the locked-rotor currents indefinitely does not apply to fire pump motor conductors [695.4(B)(1)].
Q. Must the offsets at outlet boxes be counted toward the total amount of bends between pull boxes for EMT?
A. Yes. To reduce the stress and friction on the conductor insulation, the total amount of bends between pull points must not exceed 360° [358.26]. This includes all bends — even the small ones at the outlet boxes.
Q. Can I put two wires under a single terminal?
A. The answer is generally no. However, two conductors can be placed under the same terminal, if the terminal is identified for this purpose, either within the equipment instructions or on the terminal itself [110.14(A)]. Careful, each grounded (neutral) conductor within a panelboard, must terminate to an individual terminal [408.41].
Q. Can I install Type NM cable inside a raceway that is located in a dry location?
A. Yes, but the cable must be protected from abrasion by a fitting installed on the end of the raceway [300.15(C) and 334.30].
Q. Does the NEC address the height of wiring devices, such as receptacles and light switches, in commercial buildings?
A. There is no mounting height requirement for receptacles noted, but all light switches must be located so they can be operated from a readily accessible location. The maximum height of the operating handle can't be more than 6 feet, 7 inches in the ON position [404.8(A)]. Commercial occupancies may require the devices to be accessible to disabled persons in accordance with the American Disabilities Act.
Q. What are the NEC requirements on grounding gas piping?
A. Gas piping can't be used as a grounding electrode [250.52(B)(1)]; however, it must be bonded if it is likely to be become energized [250.104(B)]. The equipment grounding (bonding) conductor for the circuit that may energize the piping can serve as the bonding means. So effectively, this means that no action is actually required by the electrical installer in this case.
Q. Can power conductors for an intercom system be mixed in the same raceway with the audio output conductors?
A. No. 640.9(C) requires that audio output circuits utilizing Class 2 or Class 3 wiring methods not be placed in any enclosure, raceway, or cable with conductors of electric light, power, Class 1, and nonpower-limited fire alarm circuits [725.55].
Q. What type of wiring method must I use for 24V lighting supplied by a 1.5 kVA transformer?
A. Low-voltage lighting of less than 100VA can be wired in accordance with the requirements of a Class 2 circuit [725.52]. However, low-voltage lighting over 100 VA is no longer considered a Class 2 circuit and must be wired with a Chapter 3 wiring method (pipe, wire, and/or cable) in accordance with 300.3.