Article 110 Requirements for Electrical Installations; Article 210 Branch Circuits; Article 230 Services; Article 250 Grounding and Bonding; Article 310 Conductors for General Wiring; Article 338 Service Entrance Cable: Types SE and USE; Article 680 Swimming Pools, Fountains, and Similar Installations; Parts of the 2008 edition of the Guide Information for Electrical Equipment, published by Underwriters Laboratories Inc., also are mentioned.
Grounding conductor protection
Does a grounding-electrode conductor require installation in a metal raceway where it passes through a bored hole in a wood floor joist on its way to the metal water pipe under the building?
Where subject to physical damage, a grounding-electrode conductor smaller than 4 AWG must be protected. A 6 AWG could be protected from damage by the way it is installed along a building surface. Otherwise, it requires physical protection by installation as prescribed in 250.64(B). A grounding-electrode conductor smaller than 6 AWG, requires protection by installation in rigid metal conduit, intermediate metal conduit, electrical metallic tubing, rigid nonmetallic conduit or cable armor. Aluminum is not allowed when within 18 inches of the earth under the building.
Ferrous metal raceways enclosing the grounding-electrode conductor must be continuous or made continuous from the service enclosure to the metal water pipe by installing bonding jumpers at all points where the raceway is not continuous. This may be accomplished with bonding jumpers installed between the grounding-electrode conductor and cabinets, enclosures or raceways.
The grounding-electrode conductor connection to the metal water pipe also must be accessible. These requirements are in 250.64 and 250.68 of the National Electrical Code (NEC).
Wiring combination-type AFCIs
I plan to install some arc-fault circuit interrupters (AFCIs) downstream from the distribution panel in three existing residences. Fuses protect the existing service panelboards. I plan to use steel armored cable, Type AC, from the panelboard to the AFCIs as permitted by the Exception to 210.12(B). What wiring methods are permitted to extend the branch circuits to receptacles, luminaires and other appliances that will be protected by the AFCIs?
The wiring method permitted on the load side of the AFCIs is not specified. Therefore, any wiring method permitted by the NEC is acceptable. If the existing wiring method does not include an equipment-grounding conductor, the absence of this conductor will not have any adverse effect on the operation of the AFCI.
Steel-jacketed armored cable is acceptable by the exception from the panelboard to the AFCI device but does not have to be used beyond it. The existing wiring, if Code-compliant, is acceptable from the AFCI to the loads on the branch circuit.
Is there a benefit to using 90°C insulated conductors over 75°C insulation since the maximum temperature marked on panelboards, luminaires and receptacles is 60°C or 75°C?
Yes, there is an advantage to using 90°C insulated conductors where derating is required by Tables 310.15(B)(2)(a), 310.15(B)(2)(c) or other parts of the NEC.
Let’s assume we have two sets of three-wire, three-phase circuits in a single raceway. Table 310.15(B)(2)(a) requires these conductors to be derated because there are six current-carrying conductors. We will use 3/0 AWG copper conductors for this example.
Temperature limitations for conductor terminations are given in 110.14(C). Part (b) in (C)(1) of this section covers terminations for circuits over 100 amperes, and a part reads: “Termination provisions of equipment for circuits rated over 100 amperes or marked for conductors larger than 1 AWG shall be used only for one of the following: (1) Conductors rated 75°C (167°F), (2) Conductors with higher temperature ratings provided the ampacity of such conductors does not exceed the 75°C (167°F) ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors.”
The ampacity of 3/0 AWG copper conductors with 90°C insulation as shown in Table 310.16 is 225. These conductors must be derated to 80 percent of this value (0.80 × 225 = 180). If 75°C insulation is used, the derated ampacity is 160 (0.80 × 200). Since 180 amperes is less than the 75°C ampacity of the 3/0 AWG copper conductors, the corrected ampacity of the conductors is 180, a gain of 20 amperes over the 75°C temperature.
The increased current that the conductors can carry increases the voltage drop, and the fine print note following 310.15(A)(1) points this out.
Size of ground rods
Does the NEC permit 1⁄2-inch ground rods for the grounding electrode on a 200-ampere service?
Yes, ground rods may be used on any size service, feeder or branch circuit. The minimum length permitted by Section 250.52 (A)(5) is 8 feet. The minimum diameter of the rod is ? inch unless the rod is listed; then a ½-inch diameter is acceptable.
The Underwriters Laboratories Inc. (UL) directory of Guide Information for Electrical Equipment published in April 2008 contains this information on ½-inch diameter ground rods: “Ground rods are solid copper, solid stainless steel, copper-jacketed steel, stainless steel jacketed, galvanized, and chemically charged. They are not less than 0.5-inch diameter and not less than 8 feet long and capable of being driven to a depth of 8 feet. If other than circular, they have a periphery not less than 1.6-inch and a minimum thickness of not less than three-eighth-inch.
“Ground rods are marked with the rod length, the manufacturers name and catalog number within 12-inches of the top of the rod.”
Lighting in a utility room
An electric furnace and water heater are installed in a small utility room. Overhead ducts and pipes make it impossible to install a ceiling luminaire in this room. Can the luminaire be located just outside of the utility room, or can the hall light provide proper illumination for the utility room?
Acceptance of a luminaire outside of the utility room is a judgment call for the electrical inspector. Is there any space on a wall in the utility room? If there is space on the ceiling to mount an outlet box, a pendant lampholder or wall-mounted luminaire controlled by a wall switch meets the requirements of Section 210.70(A)(3). A receptacle also is required in an accessible location for servicing the heating equipment. This requirement is in Section 210.63.
Recessed luminaires in fire-rated ceiling
How are recessed luminaires identified for installation in a fire-rated ceiling?
Recessed luminaires that are suitable to installation in a fire-rated ceiling are listed as suitable for installation with the NEC and are classified for installation in a fire-rated ceiling. They have a listing mark and classification mark. The classification mark indicates the luminaire has been tested for fire resistance. The standards used by UL are ANSI/UL263 “Fire Tests of Building Construction and Materials” and ANSI/UL 1598 “Luminaires.”
Cable with a bare neutral
Can service entrance cable with a bare neutral be used for a 150-ampere service for a one-family dwelling?
Service-entrance cable that has a flame-retardant, moisture-resistant covering is suitable for use as service-entrance conductors. A bare neutral also is acceptable. An uninsulated conductor is permitted for use as a grounded conductor (may be a neutral) where used as service-entrance conductors. This is permitted by the exception in Section 338.10(B)(2).
A bare grounded-service conductor also is permitted for overhead service conductors by the exception to Section 230.22. Since service-entrance cable is available with a reduced size bare conductor, it is necessary to ensure the bare grounded conductor has adequate ampacity for the calculated load. Section 338.120 points out the service-entrance cable may have a bare conductor that is smaller than the insulated conductors. The minimum size bare conductor cannot be smaller than shown in Table 250.66 and is based on the size of the ungrounded conductors in the cable assembly.
Steel-encapsulated pool bonding
How does a swimming pool contractor bond the structure where the concrete reinforcing rods are all encapsulated?
The answer is in 680.26 and is quite long and rewritten in the 2008 edition of the NEC. Part (B) of this section requires 8 AWG bare copper conductors to be bonded to each other at crossing points. This wire mesh must conform to the contour of the pool and the pool deck. This mesh must be arranged in a 12-by-12-inch configuration with tolerance of not more than 4 inches. On the bottom of the pool, this mesh must be no more than 6 inches below the contour of the pool shell.
A copper wire mesh also is required around the exterior of the pool that extends out 3 feet beyond the inside walls of the pool. This grid must be attached to the pool grid in at least four places, placed uniformly around the pool.
Part (B)(2)(b) of Section 680.26 provides an alternate method for bonding where the reinforcing steel is encapsulated.
All metal forming shells for underwater lighting fixtures must be bonded.
All metal fittings are greater than 4 inches in any dimension and that penetrate the pool structure are required to be bonded. All metal raceways and metallic equipment must be bonded to the pool-bonding system. However, it is not necessary to bond a double-insulated water pump, but an 8 AWG copper wire must be provided above ground where the pump is located to provide bonding of a replacement pump that is not double-insulated.
For a complete understanding of all of the requirements for bonding of swimming pools, carefully read Section 680.26.
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. Questions can be sent to firstname.lastname@example.org.