Article 110 Requirements for Electrical Installations
Article 230 Services
Article 406 Receptacles, Cord Connectors and Attachment Plugs (Caps)
Article 408 Switchboards and Panelboards
Article 410 Luminaires (Lighting Fixtures), Lampholders and Lamps
Article 440 Air-Conditioning and Refrigeration Equipment
Article 450 Transformers and Transformer Vaults
Q: I have a 400-ampere, 480Y/277-volt service switchboard that is 6½ feet wide, 6 feet tall and 2 feet deep that is to be installed in an electric equipment room in a two-story office building. What are the requirements for working space and exit doors in this equipment room?
A: First of all, the service equipment must be readily accessible. This requirement appears in 230.70(A)(1). And a definition for “Accessible, Readily” appears in Article 100.
Clear spaces around electrical equipment are given in 110.21. Working space is required by 110.26(A) and depends on what is on the other side of the working space. Table 110.26(A)(1) shows minimum clear space required for three different conditions. These spaces vary from 3 to 4 feet. Three feet of space is required where there are no exposed live parts or grounded surfaces on the other side of the work space, and 3½ feet is required where there are grounded surfaces (concrete, brick, etc.) on the other side of the work space. A minimum of 4 feet is required where exposed live parts are on both sides of the work space.
No working space is required at the sides or in back of the switchboard if there are no connections, renewable or adjustable parts that must be serviced from the sides or back.
The width of the working space must be at least the width of the switchboard. This requirement is in 110.26(A)(2).
The minimum headroom for the working space is 6½ feet or the height of the electrical equipment if it is more than 6½ feet high.
Working space and the switchboard must have illumination to comply with part D of 110.26. One entrance that is at least 2 feet wide by 6½ feet high must be provided. (See 110.26(C)(1).)
Space above the switchboard must not contain any foreign piping or ducts. This unobstructed space extends for a height of 6 feet, or to the structural ceiling, to allow for the installation of conduit, cable, bus duct and other wiring methods from the switchboard. Any foreign piping containing liquids installed above this space must be provided with drip pans to prevent leaks or breaks in the piping from damaging the electrical equipment.
Sealing for temperature changes
Q: Are seal-offs required in conduits that supply lighting and blower motors in commercial walk-in coolers in restaurants?
A: Yes, the raceway must be filled with an approved material to prevent the passage of warm air to the cold section of the raceway. This requirement was changed in the 2002 edition of the National Electrical Code (NEC) to include raceways that run from the interior to the exterior of buildings where condensation is a problem. The raceway can be filled with Duct Seal to prevent air circulation. An explosion-proof seal is not required.
Responsibility for doors to electrical equipment rooms
Q: Is it the electrical inspector’s responsibility to see to it that proper doors and door hardware are provided for electrical equipment rooms that have switchgear rated above 2,000 amperes and more than 6 feet wide? Since carpenters install doors, it is my opinion that doors are the building inspector’s responsibility.
A: Requirements for the size, location, swing and hardware for doors that lead into and out of electrical equipment rooms appear in the NEC. Therefore, the person responsible for enforcement of the NEC must make sure that the doors comply with 110.26(C)(1) or (2). This is an item that should be checked by the electrical plan reviewer. Any deviation from the NEC requirements should be pointed out to the engineer/architect at this time for corrective action.
Specific requirements for doors to electrical switchgear rooms are that they be at least 2 feet wide by 6½ feet high and located at each end of the working space. (under some conditions only one door is required.) The door(s) must open in the line of egress, and be equipped with panic bars, pressure plates or other devices that allow the door to unlatch and open under simple pressure.
If the electrical plan checker does a thorough job during the plan review process, there should be no problem with doors and door hardware on the construction site.
Q: I have a job to wire some free-standing portable showcases for a department store. I planned to install receptacles at the ends of each case and plug them together with short cords, but was told that was not acceptable. Are cord- and plug-connected showcases prohibited by the NEC?
A: Cord-connected showcases are permitted by the NEC, but they cannot be wired as you propose. There are stringent and detailed requirements for wiring of moveable showcases in 410.29. Here are some of them. Flexible cords must be hard-service type with an ampacity that is equal to or greater than the ampere rating of the branch circuit overcurrent device protecting the permanent receptacle that supplies the showcase. Locking-type connectors must be used to couple the showcases together. Receptacles, connectors and attachment plugs must be listed, grounding type and rated 15 or 20 amperes. Flexible cord under the showcases must be secured and protected from mechanical damage and the wiring has to be designed to limit the space between showcases to 2 inches. The full length of cord from the first showcase to the supply receptacle cannot be more than 12 inches. There are a few other restrictions that apply to wiring and electrical equipment associated with portable showcases, but I have mentioned those that are most important. You should completely understand the requirements in 410.29 before doing the work.
The proposed method of connecting the showcases also violates 406.6. This part (B) does not permit attachment plugs at both ends of a length of flexible cord. The first sentence of this part says: “Attachment plugs shall be installed so that their prongs, blades, or pins are not energized unless inserted into an energized receptacle.”
Panelboard overcurrent protection
Q: A 225-ampere, three-phase, four-wire, 208Y/120-volt panelboard contains the following three-pole and one-pole circuit breakers: 6—15-ampere, three-pole cbs for three-phase motors; 4—20-ampere, three-pole cbs for three-phase motors; 2—40-ampere, three-pole cbs for three-phase motors; 2—20-ampere, one-pole cbs for lighting. This panelboard is served from a 75-kVA, three-phase, 480-volt transformer. Overcurrent protection for the transformer is provided by 125-ampere, time-dela4y fuses. According to Table 450.3(B), overcurrent protection for the transformer secondary is not required, but I am not sure about the panelboard. Is overcurrent protection for the panelboard required?
A: Your statement that secondary overcurrent protection for the secondary windings of the transformer is not required is correct because transformer primary overcurrent protection of 125-amperes meets the requirement for overcurrent protection of the primary only. Here is the calculation: Primary current = transformer kVA * 1,000 ÷ by 480 * the square root of 3. This results in a full-load current of 90.3 amperes. Table 450.3(B) allows primary overcurrent protection to be 125 percent of primary current with permission to increase to the next-larger standard size of fuse or circuit breaker where the calculated current does not match a standard size shown in 240.6. Multiplying 90.3 amperes by 1.25 results in a current of about 113 amperes. The next standard size above 113 is 125. Therefore, overcurrent protection for the secondary is not required.
Panelboards are classified as “Lighting and Appliance Panelboards” or as “Power Panelboards” in 408.14. The panelboard described in this question fits the definition of a “Power Panelboard”: “A power panelboard is one having 10 percent or fewer of its overcurrent devices protecting lighting and appliance branch circuits.” A lighting and appliance branch circuit is defined as a branch circuit that has a connection to the neutral bus and overcurrent protection not greater than 30 amperes.
Part (B) of 408.16 requires a single overcurrent device for protection of this panelboard. The ampere rating of the overcurrent device cannot be greater than the ampere rating of the panelboard. This overcurrent device can be located in the panelboard or on the supply side of the panelboard.
Air-conditioning disconnecting means
Q: Is a circuit breaker not marked “HACR” permitted as the disconnecting means for an outside air-conditioning condensing unit?
A: If the data plate on the condensing unit specifies Fuses or an “HACR-Type Circuit Breaker”, one of these types of overcurrent protection must be in the branch circuit. Assuming that an HACR circuit breaker is permitted, this type may be installed in the panelboard that supplies the outdoor condensing unit, and a circuit breaker without the HACR designation may be located at the unit and serve as the disconnecting means required by 440.14. A molded case switch or a nonfused switch with a proper horsepower rating could also serve as the required disconnect mentioned in 440.14, but somewhere in the branch circuit, a properly rated and marked HACR- type circuit breaker or a switch and fuses must be provided. EC
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.254.2132.