NEC Questions and Answers, Based on the 2008 NEC
November 2009 – Part 1
By Mike Holt for EC&M Magazine
Here’s the follow up to Friday’s newsletter. This includes all of the answers to the questions sent, so you can see how you did.
Q1. We are told that we must GFCI protect our drinking fountain, but the receptacle is buried behind the unit. Do we really have to do this?
A1. All electric drinking fountains must be GFCI-protected [422.52], but if you are really concerned about accessibility, it you can always use a GFCI breaker for the protection.
Q2. What are the NEC requirements when replacing 15A or 20A, 125V receptacles?
A2. See 406.4(D) as follows:
Grounding-Type Receptacles. Where an equipment grounding conductor exists, grounding-type receptacles must replace nongrounding-type receptacles, and the receptacle’s grounding terminal must be connected to an equipment grounding conductor in accordance with 406.4(C) or 250.130(C).
Nongrounding-Type Receptacles. 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 one of the following:
- Another nongrounding-type receptacle.
- A GFCI-type receptacle marked “No Equipment Ground.”
- A grounding-type receptacle, if GFCI protected and marked “GFCI Protected” and “No Equipment Ground.”
Author’s 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’s 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).
GFCI Protection Required. When existing receptacles are replaced in locations where GFCI protection is currently required, the replacement receptacles must be GFCI protected. This includes the replacement of receptacles in dwelling unit bathrooms, garages, outdoors, crawl spaces, unfinished basements, kitchen countertops, rooftops, or within 6 ft of laundry, utility, and wet bar sinks. See 210.8 in this textbook for specific GFCI-protection requirements.
Q3. When are tamper resistant receptacles required?
A3. The rule for tamper resistant receptacles applies only to dwelling units. All 15A and 20A, 125V receptacles required in the following areas of a dwelling unit [210.52] must be listed as tamper resistant [406.11]:
• Wall Space—210.52(A)
• Small-Appliance Circuit—210.52(B)
• Countertop Space—210.52(C)
• Bathroom Area—210.52(D)
• Outdoors—210.52(E)
• Laundry Area—210.52(F)
• Garage and Outbuildings—210.52(G)
• Hallways—210.52(H)
Q4. What are the bonding requirements for transformers?
A4. Please review 250.30(A) as follows:
System Bonding Jumper. A system bonding jumper must be installed at the same location where the grounding electrode conductor terminates to the neutral terminal of the separately derived system; either at the separately derived system or the system disconnecting means, but not at both locations [250.30(A)(5)].
Installed at the Source. The system bonding jumper must connect the neutral conductor to the equipment grounding conductor of the metal transformer case.
• Installed at the First Disconnecting Means. The system bonding jumper must connect the neutral conductor to the equipment grounding conductor of the metal disconnecting means enclosure.
Author’s Comment: A system bonding jumper is a conductor, screw, or strap that bonds the metal parts of a separately derived system to a system neutral point [250.2] and it’s sized to Table 250.66 in accordance with 250.28(D).
DANGER: During a ground fault, metal parts of electrical equipment, as well as metal piping and structural steel, will become and remain energized providing the potential for electric shock and fire if the system bonding jumper isn’t installed.
Supply Side Bonding Jumper. If the separately derived system and the first disconnecting means are located in separate enclosures, a supply side equipment bonding jumper must be run to the secondary system disconnecting means. Where the supply side equipment grounding conductor is of the wire type, it must be sized in accordance with Table 250.66, based on the area of the largest ungrounded secondary conductor in the raceway or cable. This conductor is not required to be larger than the derived circuit conductors.
Question: What size supply-side bonding jumper is required for flexible metal conduit containing 300 kcmil secondary conductors?
(a) 3 AWG (b) 2 AWG (c) 1 AWG (d) 1/0 AWG
Answer: (b) 2 AWG [Table 250.66]
System Bonding at Disconnect. Where the system bonding jumper is installed at the disconnecting means instead of at the source, the following requirements apply:
- Sizing for Single Raceway. Because the secondary neutral conductor serves as the effective ground-fault current path for ground-fault current, it must be routed with the secondary conductors and sized not smaller than specified in Table 250.66, based on the area of the secondary conductors.
- Parallel Conductors. If the secondary conductors are installed in parallel, the secondary neutral conductor in each raceway or cable must be sized not smaller than specified in Table 250.66, based on the area of the largest ungrounded conductor in the raceway or cable. In no case is the neutral conductor permitted to be smaller than 1/0 AWG [310.10(H)].
Author’s Comment: Where the system bonding jumper is installed at the disconnecting means instead of at the source, an equipment bonding conductor must connect the metal parts of the separately derived system to the neutral conductor at the disconnecting means in accordance with 250.30(A)(2).
Q5. I need to run a feeder to a pool house panel, what are the wiring methods required for this installation?
A5. The requirements are contained in 680.25 as follows:
(A) Wiring Methods. Feeder conductors to panelboards containing permanently installed pool, outdoor spa, or outdoor hot tub equipment circuits must be installed in rigid metal conduit, intermediate metal conduit, liquidtight flexible nonmetallic conduit, or PVC conduit. Electrical metallic tubing is permitted where installed on or within a building, and electrical nonmetallic tubing is permitted where installed within a building.
Ex: Branch circuits for permanently installed pool, outdoor spa, or outdoor hot tub equipment can originate from an existing panelboard where the existing feeder contains an equipment grounding conductor within the outer sheath of a cable.
(B) Equipment Grounding Conductor. An insulated copper or aluminum equipment grounding conductor must be installed with the feeder conductors between the grounding terminal of the pool, outdoor spa, or outdoor hot tub equipment panelboard and the grounding terminal of the applicable service equipment.
(1) Size. This feeder equipment grounding conductor must be sized according to 250.122, but not smaller than 12 AWG.
(2) Separate Buildings. Where a feeder is run to a separate building or structure to supply permanently installed swimming pool, outdoor spa, or outdoor hot tub equipment, an insulated equipment grounding conductor must be installed with the feeder conductors to the disconnecting means at the separate building or structure [250.32(B)].
Q6. What are the grounding requirements for satellite dishes?
A6. The grounding of satellite dishes are contained in 810.21.
Author’s Comment: Grounding the lead-in antenna cables and the mast help prevent voltage surges caused by static discharge or nearby lightning strikes from reaching the center conductor of the lead-in coaxial cable. Because the satellite dish sits outdoors, wind creates a static charge on the antenna as well as on the cable attached to it. This charge can build up on both the antenna and the cable until it jumps across an air space, often passing through the electronics inside the low noise block down converter feedhorn (LNBF) or receiver. Connecting the coaxial cable and dish to the building grounding electrode system (grounding) helps to dissipate this static charge.
Nothing can prevent damage from a direct lightning strike,, but grounding with proper surge protection can help reduce damage to the satellite dish and other equipment from nearby lightning strikes.
(A) Material. The grounding conductor to the electrode [810.21(F)] must be copper or other corrosion-resistant conductive material, stranded or solid.
(B) Insulation. Insulated, covered or bare.
(C) Supports. The grounding conductor must be securely fastened in place.
(D) Mechanical Protection. The grounding conductor must be mechanically protected where subject to physical damage, and where run in a metal raceway both ends of the raceway must be bonded to the grounding conductor.
Author’s Comment: Installing the grounding conductor in PVC conduit is a better practice.
(E) Run in Straight Line. The grounding conductor must be run in as straight a line as practicable.
Author’s Comment: Lightning doesn’t like to travel around corners or through loops, which is why the grounding conductor must be run as straight as practicable.
(F) Electrode. The grounding electrode conductor must terminate in accordance with (1), (2), or (3).
(1) Buildings or Structures With an Intersystem Bonding Termination. The grounding conductor for the antenna mast and antenna discharge unit must terminate to the intersystem bonding terminal [Article 100 and 250.94].
Author’s Comment: Bonding all systems to the intersystem bonding termination helps reduce induced potential (voltage) differences between the power and the radio and television systems during lightning events.
(2) In Buildings or Structures Without Intersystem Bonding Termination. The grounding conductor for the antenna mast and antenna discharge unit must terminate to the nearest accessible location on the following:
(1) Building or structure grounding electrode system [250.50].
(2) Interior metal water piping system, within 5 ft from its point of entrance [250.52(A)(1)].
(3) Accessible means external to the building, as covered in 250.94.
(4) Nonflexible metallic service raceway.
(5) Service equipment enclosure.
(6) Grounding electrode conductor or the grounding electrode conductor metal enclosure.
(3) In Buildings or Structures Without a Grounding Means. The grounding conductor for the antenna mast and antenna discharge unit must terminate to the nearest accessible location on the following:
(1) Any individual electrodes described in 250.52
(2) Structural steel grounded in accordance with 250.52(A)(2)
(G) Inside or Outside Building. The grounding conductor can be run either inside or outside the building.
(H) Size. The grounding conductor must not be smaller than 10 AWG copper or 17 AWG copper-clad steel or bronze.
Author’s Comment: Copper-clad steel or bronze wire (17 AWG) is often molded into the jacket of the coaxial cable to simplify the grounding of the satellite dish by eliminating the need to run a separate grounding conductor to the dish [810.21(F)(2)].
(J) Bonding of Electrodes. Where a ground rod is installed to serve as the grounding electrode for the radio and television equipment, it must be connected to the building’s power grounding electrode system with a minimum 6 AWG conductor.
(K) Electrode Connection. Termination of the grounding conductor must be by exothermic welding, listed lugs, listed pressure connectors, or listed clamps. Grounding fittings that are concrete-encased or buried in the earth must be listed for direct burial [250.70].
Q7. A conduit contains six current-carrying 10 AWG THHN conductors on a roof for a photovoltaic system, where the ambient temperature 94ºF and the ambient temperature add is 60ºF in accordance with Table 310.15(B)(2)(c). How do I determine the conductor ampacity for this condition of use?
A7. When conductors are installed in an ambient temperature other than 78°F to 86°F, ampacities listed in Table 310.16 must be corrected in accordance with the multipliers listed in Table 310.16. Where the number of current-carrying conductors in a raceway or cable exceeds three, the allowable ampacity of each conductor, as listed in Table 310.16, must be adjusted in accordance with the adjustment factors contained in Table 310.15(B)(2)(a) and 310.15(B)(2)(c). When both of these conditions exist, you must do both calculations, but you can start with the 90°C ampacity for the calculations [110.14(C)(1)].
Table 310.16 ampacity if 10 AWG THHN is 40A
Ambient Temperature Correction [Table 310.16] = .58, based on 154ºF
Conductor Bundle Adjustment [310.15(B)(2)(a)] = 0.80, six current-carrying conductors
Adjusted Ampacity = 40A x .58 x 0.80
Adjusted Ampacity = 18.56 or 19A
Q8. We got written up for having our underground conduits too close together. I know you can’t bundle cables together, but I didn’t think this applied to raceways too. Does it?
A8. Actually it does, 310.15(B)(2)(b) states that spacing between conduits, tubing, or raceways must be maintained, although the code doesn’t say what the spacing is, or how to adjust when the spacing is not maintained. Hopefully the next Code cycle will have better language for this rule…
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