Article 110—Requirements for Electrical Installations
Article 240—Overcurrent Protection
Article 310—Conductors for General Wiring
Article 410—Lighting Fixtures, Lampholders, Lamps, and Receptacles
Article 424—Fixed Electric Space-Heating Equipment
Article 430—Motors, Motor Circuits, and Controllers
Article 517––Grounding in Patient Care Areas
Electrically heated bathroom floors
Q: Ground fault circuit interrupter (GFCI) protection is required where electrically heated floors are installed in bathrooms, hydromassage bath tub, spa, and hot tub locations where these locations have conductive floor coverings. Would you provide some examples of conductive floor coverings?
A: This requirement appears in Section 424-44(g) and has the title: “Ground-Fault Circuit-Interrupter Protection for Conductive Heated Floors of Bathrooms, Hydromassage Bathtub, Spa, and Hot Tub Locations.” It requires GFCI protection of the electric floor heating system where the floor has a conductive covering.
Some examples are concrete, terrazzo, vinyl tile and vinyl sheet material containing conductive particles, and asphalt tile.
Actually, it’s not a bad idea to provide GFCI protection for all electrically heated floors in these locations because of the intermittent presence of water on the floor, and people with bare feet are usually in these areas.
There were two proposals to revise Section 424-44(g). One suggested removing “conductive” and “conductive floor coverings,” and the other added a sentence to describe conductive floor coverings. Code Making Panel 20 decided to delete the reference to “conductive floor coverings.” In the 2002 National Electrical Code (NEC), this revision will require GFCI protection for all electrically heated floors that are installed in these locations.
Transfer switches for on-site generators
Q: Do any rules in “Article 230—Services” allow transfer switches to be connected ahead of the service disconnecting means for a one-family dwelling or small commercial building with a standby generator? If the answer is “yes,” does the transfer switch become the service disconnecting means? Should the transfer switch contain overcurrent protective devices, and be marked “suitable for use as service equipment?”
A: Although Section 230-83 with the title “Transfer Equipment” was removed from the 1999 edition of the NEC, I believe that one or more of the five items mentioned in Section 230-82 allow a transfer switch as part of the service equipment.
Where a transfer switch is connected on the supply side of the service overcurrent protection and disconnecting means, it must be marked, “Suitable for Use as Service Equipment.” Because a transfer switch used in this manner does not have to be readily accessible, it may be installed more than 6 feet 7 inches above the ground, floor, or working platform.
The transfer switch is not the service disconnecting means, and usually does not contain fuses or a circuit breaker. If fuses or a circuit breaker are included in the transfer switch enclosure, Section 240-24(a) requires that the overcurrent devices be readily accessible.
Molded case switch used as motor disconnect
Q: I have to install the wiring and equipment for a three-phase 230-volt, 5-horsepower motor with a full-load current of 14.8 amperes. The length of the branch circuit is less than 50 feet. Is No. 14 copper wire with Type THWN insulation acceptable for this circuit? Can a 15-ampere molded case switch be used for the motor disconnect? Where can I find the horsepower rating for this switch?
A: For motor circuit conductor ampacity, Section 430-6 requires that the full-load current shown in Table 430-150 be used, and Section 430-22 requires that this current be multiplied by 125 percent to obtain the minimum motor branch circuit conductor ampacity.
The Table value of full-load current for a three-phase, 230-volt, 5-horsepower induction motor is 15.2 amperes. Multiplying this figure by 1.25 results in a minimum motor branch circuit conductor ampacity of 19. According to Table 310-16, No. 14 copper wire with 60 degrees Celsius or 75 degrees Celsius insulation has an ampacity of 20, and Section 240-3(g) allows the overcurrent protection to be determined by the requirements in Section 430-52. Therefore, No. 14 copper conductors may be used for the motor branch circuit.
Section 430-52 indicates that the motor branch circuit short-circuit and ground fault protection is selected from Table 430-152. This table allows dual-element time-delay fuses to be sized at 175 percent of motor full-load current, or 250 percent of motor full-load current for an inverse-time circuit breaker.
The calculations show that 30-ampere dual-element time-delay fuses or a 40-ampere, three-pole, inverse-time circuit breaker satisfy this Section.
Molded case switches are generally circuit breaker enclosures without current sensing elements. They look like circuit breakers and fit in circuit breaker panelboards.
All listed molded case switches are tested for interrupting rating at six times their current rating. Therefore, all list molded case switches are acceptable as motor disconnects, provided that they have an ampere rating that is at least 115 percent of the full-load current of the motor. This means that a 20-ampere molded case switch is required for the 5-horsepower motor mentioned in the question. The Code references for these requirements are Sections 430-109 and 430-110.
Parking lot lighting poles
Q: Do outdoor metal poles that are 20 feet long have to be listed by a recognized independent testing laboratory or can an electrical inspector determine if the poles meet the requirements in the NEC? The poles are aluminum and will be used at a supermarket parking lot.
A: I am not aware of any recognized independent testing laboratory that “lists” metal poles for support of lighting fixtures. However, Underwriters Laboratories Inc. has a classification-marking program for luminaire poles under guide (IEUR).
Poles are inspected for suitability of the enclosure for supply conductors, provision of equipment bonding or grounding means, and access to the interior wiring. They are not tested for wind loading or mechanical strength.
A qualified electrical inspector should be able to accept or reject an aluminum lighting pole without third-party certification, since there are rules in the NEC that cover the subject. The inspector should look at and feel the inside of the pole to make sure it is smooth and free of sharp edges that could damage conductor insulation; measure the opening for the handhole, making sure that it is at least 2 inches by 4 inches and provided with a raintight cover; and look for a grounding terminator lug that is accessible from the handhole.
I believe there is enough information in Section 410-15(b) for an experienced inspector to evaluate a lighting fixture pole for compliance with the NEC without certification by an independent testing laboratory.
Surface-mounted fluorescent fixtures
Q: Is 1½ inches of space required between a fluorescent fixture with class P ballasts and a low-density cellulose fiberboard ceiling? Can the spacing requirements be ignored because the ballasts are thermally protected? Is plywood, particle board, or paneling considered to be low-density cellulose fiberboard?
A: The requirement for 1½ inch spacing applies to all surface-mounted fixtures that contain ballasts including those ballasts that have thermal protection. The requirement is in Section 410-76(b), and includes a Fine Print Note that explains what is meant by the term “low-density cellulose fiberboard.”
Plywood, wood particle board, wood panels, and gypsum board are not low-density cellulose fiberboard. Therefore, fluorescent fixtures can be secured directly to, or be in contact with, these materials.
One example of low-density cellulose fiberboard is acoustic ceiling tile that is manufactured from bagasse, which is what remains of sugar cane after the juice is extracted. This product was often called celotex.
The long Fine Print Note following Section 410-76(b) provides guidance in determining whether a building material is low-density cellulose fiberboard or not.
Where derating is necessary because there are more than three current-carrying conductors in the same cable assembly, the 90 degrees Celsius ampacity for Type THHN insulation can be used, but the corrected ampacity cannot exceed the value shown in the 75 degrees Celsius column of Table 310-16. Also, conductor terminations must comply with the rules in Section 110-14(c).
Redundant Grounding in Patient Care Areas
Q: A wall-mounted fluorescent lighting fixture is installed 7 feet above the floor in a patient care room of a hospital. The fixture is supplied by electrical metallic tubing with an insulated equipment grounding conductor. From the junction box in back of the fixture interlocked metal tape type MC cable with an equipment grounding conductor is run to a wall switch that is about 8 feet from the edge of the patient bed. Is this installation Code compliant?
A: Yes, the installation satisfies Exception No. 3 to Section 517-13(a). This exception does not require redundant grounding for lighting fixtures located more than 7½ feet above the floor and switches located outside of the patient vicinity.
The phrase “patient vicinity” is defined in Section 517-3. Part of this definition describes the space within a room that extends not less than 6 feet beyond the perimeter of the bed in its normal location.
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at (504) 254-2132.