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By Mike Holt for EC&M Magazine
Q1. What size grounding electrode conductor is required for a 1200A service supplied with three sets of 600 kcmil conductors per phase?
A1. The grounding electrode conductor, when not run to a ground rod, concrete-encased electrode, or ground ring, must be size in accordance with Table 250.66. Because the equivalent area per phase equals 1,800 kcmil, the grounding electrode conductor is required to be 3/0 AWG.
Q2. Where are hospital grade receptacles required?
A2. Receptacles for inpatient sleeping beds or procedure table beds used in a critical patient care area (patient bed location) must be listed as "hospital grade" [517.18(B)].
"Hospital grade" receptacles aren't required in treatment rooms of clinics, medical and dental offices, or outpatient facilities. This is because these facilities don't have a "patient bed location" as defined in 517.2.
Q3. What is the Code requirement for splicing 14 or 12 AWG copper ground wires? My instructor says that they only need to be twisted together, and some of the local inspectors are allowing this to pass.
A3. Your instructor and inspector are wrong. Section 110.14(B) requires all conductors be spliced by a splicing device identified for the purpose or by exothermic welding. Also equipment grounding (bonding) conductors associated with circuit conductors that are spliced or terminated on equipment within a metal outlet box, must be spliced together or joined to the box with devices suitable for the purpose [250.148(A)].
Note: You don't need to twist the conductors together prior to the installation of a twist-on wire connector.
Q4. The 2005 NEC now requires all 15 and 20A, 125V receptacles located within 6 ft from the dwelling unit laundry sink to be GFCI protected. Does this apply to a single receptacle on a dedicated branch circuit for the washing machine?
A4. Yes. See 210.8(A)(7).
A5. Sure. Receptacles are permitted above a suspended ceiling, but a flexible cord is not [400.8(5)]. Why install a receptacle above a ceiling if the flexible cord is not permitted in this space? Because the receptacle could be used for portable tool and equipment, it just can't be use for cord-and-plug equipment fastened in place.
Q6. Now that the 2005 NEC requires a concrete-encased electrode of the rebar type for the service, is a ground rod still required? Note: Water service to the building is supplied by a nonmetallic raceway.
A6. Nope. The only time a concrete-encased electrode of the rebar type is not required is for existing buildings or structures where the conductive steel reinforcing bars aren't accessible without disturbing the concrete [250.50 Ex]. So in a new building or structure, you must use a concrete-encased electrode of the rebar type installed in accordance with 250.52(A)(3).
However, in existing buildings or structure, you can use a ground rod (or two) as the required grounding electrode. Just be sure to install it in accordance with 250.52(A)(5) and if a single ground rod has a resistance of more than 25 ohms, drive an additional one and bond it to the first ground rod.
Q7. The instructions for the UL listed standby generators I install state: "drive a ground rod and bond it to the frame of the generator enclosure." This generator uses a solidly bonded neutral in the transfer switch, so this generator is not a separately derived system. Why do they say it must be grounded to an approved earth ground?
A7. Probably because the engineer writing the specification for the manual and the engineer at UL who reviews the instructions think the earth serves some safety purpose. I have a standby generator with an unswitched neutral in the transfer switch and I didn't install a ground rod. The only time an earth ground is required by the NEC for a generator is when the generator meets the definition of separately derived system [250.30(A)(3)].
According to Article 100, the generator would only be a separately derived system where there's no direct electrical connection to the utility supply conductors. In other words, the neutral is also switched in the transfer switch.
A8. The equipment grounding (bonding) conductor must be sized in accordance with Table 250.122, based on the ampere rating of the circuit-protection device, but in no case is it required to be larger than the circuit conductors.
For example, a 5 hp, 208V, three-phase motor having a FLC of 16.7A, wired with 12 AWG [430.22(A)], with a 40A short-circuit ground-fault protection device [430.52(C)(1)] would have a 12 AWG equipment grounding (bonding) conductor.
Q9. Can a stranded 12 AWG wire be placed under the screws for receptacles and switches?
A9. Conductor terminations must comply with manufacturer's instructions as required by 110.3(B). For example, if the instructions for the device state "Suitable for 18-2 AWG Solid," then only solid conductors are permitted. If the instructions do not specify 'solid' such as, "Suitable for 18 - 12 AWG," then either solid or stranded conductors can be used with the terminating device.
Q10. Is a splice permitted in a panel?
A10. Yes, splices and taps can be installed in cabinets, cutout boxes, or meter socket enclosures if the splices or taps do not fill the wiring space at any cross section to more than 75 percent.
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