NEC Questions and Answers
By Mike Holt for EC&M Magazine
Q1. How far away must a receptacle outlet be from a shower or bathtub?
A2. The NEC does not require 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)].
Q2. Can circuit breakers be installed in a bathroom?
A2. Overcurrent protection devices, such as circuit breakers must not be located in the bathrooms of dwelling units, or guest rooms or 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)].
Q3. What are the bonding requirements for a hydromassage tub motor if the water piping is nonmetallic?
A3. All metal piping systems and grounded metal parts in contact with the circulating water must be bonded together using a solid copper bonding jumper not 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.
Q4. How far away must nonmetallic-sheathed cable (Romex) be from an air conditioning duct that is used to heat the home?
A4. There is no clearance requirement for Type NM Cable from a heating duct.
Q5. Do I need to use hospital grade receptacles in a chiropractor’s examining room?
A5. Hospital grade receptacles aren’t required in treatment rooms of clinics, medical and dental offices, or outpatient facilities [517.18(B)]. This is because these facilities don’t have a “patient bed location” as defined in 517.2.
Q6. Can a dishwasher be hard-wired with NM, MC, or AC cable instead of having it cord and plug connected?
A6. Yes. 422.16(B)(2) states that cords are permitted, not required.
Q7. Is a flexible wiring method required for the connection of a dry-type transformer?
A7. No. Typically in industrial settings, rigid metal conduit is used to protect the primary and secondary wiring.
Q8. I recently saw an advertisement for red conduit that is to be used for emergency circuits. Is this a code requirement?
A8. No. Section 700.9 requires all boxes and enclosures, including transfer switches, generators, and power panels for emergency circuits to be permanently marked as components of an emergency system. But this does not apply to raceways.
Q9. How do I size the circuit protection device for a fire pump motor?
A9. The circuit protective device(s) must be selected or set to carry indefinitely the sum of the locked-rotor current of the fire pump and pressure maintenance pump motor(s), and 100 percent 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)].
Question: What size conductor is required for a 25 hp, 208V, three-phase fire pump motor?
(a) 4 AWG (b) 3 AWG (c) 2 AWG (d) 1 AWG
Answer: (b) 3 AWG
Conductors are sized at 125 percent of the motor’s FLC as listed in Table 430.250
FLC of 25 hp = 74.8A, Table 430.250
Conductor = 74.8A x 1.25
Conductor = 93.5A
3 AWG at 75°C is rated 100A
The fire pump motor circuit protective device size must be set to carry indefinitely the sum of the locked-rotor current of the fire pump motor. According to Table 430.251(B), the locked-rotor current of a 25 hp, 208V, three-phase motor is 404A.
Q10. Can table 310.15(B)(6) be used to size service conductors for a duplex?
A10. Maybe. Table 310.15(B)(6) is only suitable to size 3-wire, single-phase, 120/240V service or feeder conductors (including neutral conductors) that serve as the main power feeder for an individual dwelling unit. So you can size the individual service conductors to each unit using this table, but not the service conductors for both units. Figure 310-15B6 UN310-22B
