Article 250-Grounding and Bonding
Article 312-Cabinets, Cutout Boxes, and Meter Socket Enclosures
Article 314- Outlet, Device, Pull, and Junction Boxes; Conduit Bodies; Fittings; and Handhold Enclosures
Article 350-Liquidtight Flexible Metal Conduit: Type LFMC
Article 410-Luminaires (Lighting Fixtures), Lampholders, and Lamps
Article 590-Temporary Installations
Article 700-Emergency Systems
Exits and emergency lighting
Q: Does the National Electrical Code permit the installation of four-tube fluorescent luminaries (lighting fixtures) to be used for exit and emergency lighting? One ballast in each luminaire would be connected to an emergency branch circuit and the other ballast would be connected to a branch circuit supplied by the normal source. There would be two branch circuits in each luminaire: one from the normal power and the other from the emergency system. Does the NEC permit an emergency circuit and a normal source circuit in the same luminaire?
A: There is nothing in the NEC that would prevent such an installation; however, approval by the authority having jurisdiction is required by 700.3. Although emergency-system wiring must be installed independent of all other wiring, Item 2 of 700.9(B) allows normal and emergency wiring to be together in luminaries (lighting fixtures).
The two lamps energized during emergencies must provide adequate illumination for people to safely leave the building or structure. The second paragraph of 700.16 relates to this requirement and reads like this: “Emergency lighting systems shall be designed and installed so that the failure of any individual lighting element, such as the burning out of a light bulb, cannot leave in total darkness any space that requires emergency illumination.”
There are also requirements in 410.73(E)(3) and (4) for ballasts that are used for emergency lighting. “(3) Exit Fixtures. A ballast in a fluorescent exit luminaire (fixture) shall not have thermal protection.” And “(4) Egress luminaries (Fixtures). A ballast in a fluorescent luminaire (fixture) that is used for egress lighting and energized only during a failure of the normal supply shall not have thermal protection.”
Conductors in safety switches
Q: Does the NEC permit conductors to pass through safety switches? Are splices in conductors permitted in safety switches that contain fuses?
A: The answer to both questions is yes, provided that any unspliced conductors passing through the switch plus any other conductors in the switch do not fill the wiring space to more than 40 percent or more than 75 percent where splices or taps are made in the wiring space. Part (B) of 404.3 indicates that switch enclosures cannot be used as junction boxes, auxiliary gutters or raceways for conductors feeding through or tapping off to other switches or overcurrent devices unless the enclosure complies with 312.8. And 312.8 reads like this: “Enclosures for switches or overcurrent devices shall not be used as junction boxes, auxiliary gutters, or raceways for conductors feeding through or tapping off to other switches or overcurrent devices, unless adequate space for this purpose is provided. The conductors shall not fill the wiring space at any cross section to more than 40 percent of the cross-sectional area of the space, and the conductors, splices and taps shall not fill the wiring space at any cross section to more than 75 percent of the cross-sectional area of that space.”
Liquidtight flexible metal conduit
Q: Does the National Electrical Code permit liquidtight flexible metal conduit to be unsupported or not secured for a maximum length of six feet where used as a fixture “whip” to supply fluorescent fixtures in an accessible ceiling?
A: Yes it does. A new exception No. 4 to 350.30(A) allows this. It reads as follows: “Lengths not exceeding 1.8m (6 ft) from the last point where the raceway is securely fastened for connections within an accessible ceiling to luminaire(s) [lighting fixture(s)] or other equipment.” This exception does not appear in the 2002 edition of the NEC, and therefore, is not acceptable if the 2002 edition is still being enforced in your jurisdiction.
Exception No. 3 to 350.30(A) appears in both editions and allows six feet of LFMC to be unsupported and not secured where it is used to supply tap conductors to luminaries (lighting fixtures) that require high-temperature-rated supply conductors and has limited application. It is also questionable whether this wiring method is suitable for the high temperatures encountered around some recessed lighting fixtures.
Supplementary grounding electrodes
Q: Our electrical contracting firm does electrical work in three different jurisdictions. Two of these require at least two ground rods to supplement the buried metal waterpipe that is used for the service-grounding electrode, while the other jurisdiction requires only one ground rod to supplement the waterpipe electrode. Which jurisdiction is correct? Does the NEC require two ground rods to supplement the waterpipe ground?
A: There are at least two possible answers to this question. The first is that the jurisdiction requiring a single ground rod is enforcing the 1996 edition of the National Electrical Code and the other jurisdictions are enforcing the 1999 or later editions of the NEC. In the 1996 edition, only one ground rod was required to supplement the metal waterpipe. In 1999 and later editions of the Code, at least two ground rods were required where a single rod did not have a resistance of 25 ohms or less.
Another possible answer for the jurisdiction that requires only one ground rod is the resistance of one ground rod is less than 25 ohms.
I would ask the AHJ who accepts one ground rod for the reason for doing so. If the answer is they enforce the 1996 edition of the NEC, ask when a later edition will be adopted and enforced, or drive two ground rods at every service where buried metal waterpipe is used as the grounding electrode.
Type MC cable terminations
Q: Is it necessary to use anti-short bushings on Type MC cable terminations where insulated throat connectors are used at all terminations?
A: The answer is no. In fact, anti-short bushings, although furnished in a bag with each coil of MC cable, are not required to be used by the cable manufacturer or the National Electrical Code. Manufacturers provide them and recommend that they be used to enhance safety. Insulated throat connectors are also not required but they do a better job of protecting conductor insulation from abrasion at the point where the armor is removed.
It is good practice to use the anti-short bushings provided by the cable manufacturer or to use proper-size insulated throat connectors (properly installed), but neither one is required by the NEC.
Device box barriers in snap switches
Q: Part (D) of 314.28 requires permanent barriers in boxes that contain two or more snap switches operating at 277 volts from different phases of a four-wire, 480-volt system. These barriers are required to be permanently installed. Does “permanent” mean screwed in place, welded, etc.?
A: You are correct in your statement that the word “permanent” appears in 314.28(D) and 404.8(B) in the 2002 edition of the NEC. However, the permanent barrier mentioned in 314.28(D) is used to separate one box into two boxes for determining the box size for conductor sizes and dimensions of junction and pull boxes.
The requirement in 404.8(B) deals with two or more snap switches installed in a single box. It also applies where the voltage between adjacent switches exceeds 300. This part (B) requires snap switches connected to different phases of a 480Y/277- volt system to be separated by a barrier.
In the 2002 edition, the barrier between adjacent switches had to be permanently installed. In the 2005 edition, the word permanently is removed, and this language is used “... or unless they are installed in enclosures equipped with identified, securely installed barriers between adjacent devices.” The underlined words replace “permanently.”
At least one manufacturer has a listed divider that slides into place between grooves in the outlet box. The revised wording allows the use of this barrier.
Eight-foot ground rod
Q: Does the NEC permit sawing an 8-foot ground rod in half, and driving the halves below the surface of the earth where solid rock is encountered? The two 4-foot sections are then bonded together with a 6 AWG copper conductor and connected to the neutral bus in the service panel.
A: The ground rod cannot be cut in half. At least eight feet of a continuous length must be installed. There are remedies in 250.53(G) for burying a ground rod where rock is encountered. The rod can be driven at an angle not to exceed 45 degrees from vertical or, when rock is near the surface and the 45-degree angle cannot be met, a trench at least 30 inches deep is permitted for burying the ground rod.
Use of type NM-B cable
Q: Is Type NM-B cable permitted for temporary wiring in a 12-story office building under construction?
A: Yes, Type NM cable is permitted for temporary wiring during construction. The article for Temporary Installations is 590 in the 2005 edition. It has been moved from Article 527 in the 2002 issue. Wiring methods for feeders and branch circuits are covered by 590.4(B) and (C). The last sentence in each of these parts is identical for feeders and branch circuits and reads this way: “Type NM and Type NMC cables shall be permitted to be used in any dwelling, building, or structure without any height limitation, or limitation by building construction type and without concealment within walls, floors, or ceilings.” EC
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.