NEC Questions and Answers – Based on the 2011 NEC
October 2011 - Part 2 of 2
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. If plastic pipe is used for the main water line, then it changes to copper after entering the dwelling, must the metal pipe be bonded to the electrical system?
A1. To remove dangerous voltage on metal parts from a ground fault, electrically conductive metal water piping systems, metal sprinkler piping, metal gas piping, as well as exposed structural steel members likely to become energized, must be connected to an effective ground-fault current path [250.4(A)(4)].
The metal water piping system must be bonded as required in (A)(1), (A)(2), or (A)(3). The bonding jumper must be copper where within 18 in. of the earth [250.64(A)], securely fastened to the surface on which it’s mounted [250.64(B)], and adequately protected if exposed to physical damage [250.64(B)]. In addition, all points of attachment must be accessible [250.104(A)].
(1) Building/Structure Supplied by a Service. The metal water piping system, including the metal sprinkler water piping system of a building/structure supplied with service conductors must be bonded to the:
- Service equipment enclosure,
- Service neutral conductor,
- Grounding electrode conductor of sufficient size, or
- Grounding electrode system.
The metal water piping system bonding jumper must be sized in accordance with Table 250.66, based on the cross-sectional area of the ungrounded service conductors.
Question: What size bonding jumper is required for the metal water piping system if the 300 kcmil service conductors are paralleled in two raceways?
(a) 6 AWG (b) 4 AWG (c) 2 AWG (d) 1/0 AWG
Answer: (d) 1/0 AWG, based on 600 kcmil conductors, in accordance with Table 250.66
Q2. Is the refrigerator in a dwelling unit kitchen allowed to be fed by the small-appliance circuit?
A2. The two or more 20A, 120V small-appliance branch circuits serving the kitchen, pantry, breakfast room, and dining room area of a dwelling unit [210.11(C)(1)] must serve all wall, floor and countertop receptacle outlets [210.52(C)], and the receptacle outlet for refrigeration equipment [210.52(B)(1)].
Ex 2: The receptacle outlet for refrigeration equipment can be supplied from an individual branch circuit rated 15A or greater.
Q3. Is a 15A or 20A, 125V receptacle allowed to plug in a television or other appliance above a bath tub?
A3. Receptacles must not be installed within or directly over a bathtub or shower stall [406.9(C)].
Q4. Does the Code limit the types of conductors and cables that are allowed to be installed inside raceways outdoors aboveground?
A4. Insulated conductors and cables installed in raceways in aboveground wet locations must be listed for use in wet locations according to 310.10(C) [300.9].
Q5. Does the NEC allow a dishwasher and disposal to be on the same dedicated circuit?
A5. An individual branch circuit is permitted to supply any load for which it’s rated, but in no case is the load permitted to exceed the branch-circuit ampere rating [210.23].
A 15A or 20A branch circuit is permitted to supply lighting, equipment, or any combination of both [210.23(A)].
Q6. Where are the securing and supporting requirements for Type NM cable?
A6. Staples, straps, cable ties, hangers, or similar fittings must secure Type NM cable in a manner that won’t damage the cable. Type NM cable must be secured within 12 in. of every box, cabinet, enclosure, or termination fitting, except as permitted by 314.17(C) Ex or 312.5(C) Ex, and at intervals not exceeding 4¼ ft [334.30].
Two-wire (flat) Type NM cable isn’t permitted to be stapled on edge.
Type NM cable installed in a raceway isn’t required to be secured within the raceway.
Type NM cable installed horizontally in bored or punched holes in wood or metal framing members, or notches in wooden members is considered secured and supported, but the cable must be secured within 1 ft of termination [334.30(A)].
Note: See 314.17(C) for support where nonmetallic boxes are used.
Type NM cable can be unsupported in the following situations [334.30(B)]:
- If Type NM cable is fished between concealed access points in finished buildings or structures, and support is impracticable.
- Not more than 4½ ft of unsupported cable is permitted from the last point of support within an accessible ceiling for the connection of luminaires or equipment.
Q7. What is the maximum size grounding electrode conductor required for a ground rod type of electrode?
A7. If the grounding electrode conductor is connected to a ground rod as permitted in 250.52(A)(5), that portion of the grounding electrode conductor that’s the sole connection to the ground rod isn’t required to be larger than 6 AWG copper [250.66(A)].
Q8. How many services are allowed to serve a building or structure?
A8. A building/structure can only be served by one service drop or service lateral, except as permitted by 230.2(A) through (D) [230.2].
Service laterals 1/0 AWG and larger run to the same location and connected together at their supply end, but not connected together at their load end, are considered to be a single service.
Special Conditions. Additional services are permitted for the following [230.2(A)]:
- Fire pumps
- Emergency systems
- Legally required standby systems
- Optional standby power
- Parallel power production systems
- Systems designed for connection to multiple sources of supply for the purpose of enhanced reliability.
Special Occupancies. By special permission, additional services are permitted for [230.2(B)]:
- Multiple-occupancy buildings where there’s no available space for supply equipment accessible to all occupants, or
- A building or other structure so large that two or more supplies are necessary.
Capacity Requirements. Additional services are permitted [230.2(C)]:
- If the capacity requirements exceed 2,000A, or
- If the load requirements of a single-phase installation exceed the utility’s capacity, or
- By special permission.
Different Characteristics. Additional services are permitted for different voltages, frequencies, or phases, or for different uses, such as for different electricity rate schedules [230.2(D)].
Q9. Is it allowable to cover over a junction box with building finish such as sheetrock?
A9. Boxes, conduit bodies, and handhole enclosures must be installed so that the wiring is accessible without removing any part of the building, sidewalks, paving, or earth [314.29].
Ex: Listed boxes and handhole enclosures can be buried if covered by gravel, light aggregate, or noncohesive granulated soil, and their location is effectively identified and accessible for excavation.
Q10. Is a surface extension allowed from an outlet box?
A10. Surface extensions can only be made from an extension ring mounted over a flush-mounted box [314.22].
Ex: A surface extension can be made from the cover of a flush-mounted box if the cover is designed so it’s unlikely to fall off if the mounting screws become loose. The surface extension wiring method must be flexible to permit the removal of the cover and provide access to the box interior, and equipment grounding continuity must be independent of the connection between the box and the cover.
For more NEC Practice purchase Mike Holt's NEC Practice Questions book, Based on the 2011 NEC. www.MikeHolt.com/NEC
