Electric service for grounding-electrode conductors
Q: The electric utility in our area requires the installation of a ground rod and grounding-electrode conductor in the meter socket. Is it acceptable to ground the grounded-circuit conductor (neutral) in the service-disconnect enclosure? The grounding electrodes to be connected at this point are the underground metal water pipe and the building slab reinforcing steel. This voltage is 208Y/120, three-phase.
A: Although the National Electrical Code (NEC) is not specific on this subject, there is nothing wrong with this requirement by the serving utility as far as the NEC is concerned. Part (A)(1) of 250.24 allows the grounding-electrode conductor to be connected at any accessible point from the load end of the service drop or service lateral, including the neutral bus in the service-disconnecting means. A single- ground rod may not meet the maximum resistance of 25 ohms, but the ground rod is not required by the NEC.
The grounding-electrode conductor connected to the buried metal water pipe, the concrete-encased electrode and the grounded-circuit conductor bus in the service disconnect satisfies the requirements in the NEC.
Although grounding the neutral at two different locations results in current flow through the earth, this is permitted by 250.142(A). Where the service-entrance conductors between the meter base and service disconnect are in a metal raceway, the conduit is in parallel with the neutral and carries current because the neutral bus in the meter base is fastened to the meter enclosure. This provides a parallel path for neutral current between the service disconnect and meter socket. Therefore, grounding the neutral in the meter socket by connection of a ground rod to this neutral terminal does not cause objectionable current flow mentioned in 250.6.
Overcurrent protection for busbars
Q: Field installed copper busbars are installed in a wireway. The busbars are each ½- by 2-inch copper protected by a 1,000-ampere three-pole circuit breaker. Is the overcurrent protection correct for these busbars? Should the installation comply with Article 366—Auxiliary Gutters, Article 368—Busways, or Article 376—Metal Wireways?
A: Article 366—Auxiliary Gutters should be used to inspect this installation. Although some products are marked “wireway” or “auxiliary gutter” and are listed under UL 870 “Wireways, Auxiliary Gutters and Associated Fittings,” there are some differences in Articles 366 and 376.
Auxiliary gutters are permitted to supplement wiring spaces at meter centers, distribution centers, switchboards and similar points of wiring systems and may enclose conductors or busbars. They are limited to 30 feet beyond the equipment that the gutter supplements. Metal wireways are not permitted to contain bare conductors (busbars) but the length of the wireway is not limited. Busways are defined as grounded metal enclosures containing factory-mounted, bare or insulated conductors, which are usually copper or aluminum bars, rods or tubes.
The ampacity of a bare copper bar in a sheet metal auxiliary gutter is 1,000 amperes per square inch. Therefore, the 1,000-ampere, three-pole circuit breaker satisfies 366.23.
Washer and dryer in bathroom
Q: Is a ground-fault circuit interrupter (GFCI) protected duplex receptacle required for a washer and gas dryer located in the bathroom of an apartment? The receptacle is on the wall behind the appliances. The receptacle meets the requirement of exception No. 2 for garages, which does not require a GFCI-protected receptacle. Can this exception be applied to the laundry appliances in the bathroom?
A: No. Exception No. 2 for garages cannot be stretched to include bathrooms. The first item in 210.8(A) applies to all 15- and 20-ampere, 125-volt, single-phase receptacles installed in bathrooms in dwelling units. There are no exceptions.
This requirement should not result in increased cost because 210.11(C)(3) requires a 20-ampere branch circuit for the bathroom, and 210.11(C)(2) requires a 20-ampere circuit for the laundry. Both have to be GFCI protected because 210.8(A)(1) requires GFCI protection for the receptacle installed within three feet of the outside edge of the washbasin.
HACR-type circuit breakers
Q: Our jurisdiction has adopted the 2005 edition of the National Electrical Code. I have to wire a 7.5-ton air conditioner. Part of the nameplate data is 208-volt, three-phase, maximum 60-ampere HACR circuit breaker. Is it necessary to install a HACR type circuit breaker for this unit?
A: A change in the 2005 edition of the NEC eliminated the requirement for an inverse time circuit breaker listed for group installation. This was the HACR type. Where several motors or loads are connected to a single branch circuit, Item 3 of 430.53(C)(3) now reads: “Each circuit breaker is listed and is of the inverse time type.” Notice that the words “listed for group installation” no longer appear. Therefore, a 60-ampere standard listed inverse time circuit breaker without HACR marking may be used.
Q: Are the examples of assembly occupancies listed in 518.2(A) considered to be assembly occupancies even though they cannot accommodate 100 people?
A: Although the occupancies listed in 518.2(A) may be classified as assembly occupancies in the Life Safety Code—NFPA 101, they are not considered as assembly occupancies by the NEC if they cannot accommodate 100 people. If less than 100, any of the wiring methods permitted in Chapter 3 of the NEC may be used.
Direct burial ground clamps
Q: Is a ground clamp that is marked “suitable for direct burial” permitted for installation in poured concrete?
A: This sentence appears in 250.70: “Ground clamps shall be listed for the materials of the grounding electrode and the grounding electrode conductor, and where used on pipe, rod or other buried electrodes, shall also be listed for direct soil burial or concrete encasement.” Therefore, a ground clamp marked “suitable for direct burial” is also suitable for installation in concrete.
The General Information for Electrical Equipment Directory (White Book) published by Underwriters Laboratories Inc. (UL) provides this information under the title: “Grounding and Bonding Equipment (KDER)—Ground clamps and other connectors suitable for use where buried in earth or embedded in concrete are marked for such use. The marking may be abbreviated DB for ‘direct burial’.”
Institutional kitchens and GFCI
Q: GFCI protection is required for all 125-volt, single-phase, 15- and 20-ampere receptacles installed in commercial and institutional kitchens with a sink and permanent facilities for food preparation and cooking. Does an area with a sink, refrigerator and built-in microwave oven in a nursing home require GFCI-protected receptacles?
A: Part (2) of 210.8(B) requires GFCI protection of 15- and 20-ampere, 125-volt, single-phase receptacles where permanent facilities for cooking are provided, which leaves the decision to the electrical inspector.
The question that must be answered: Does a built-in microwave oven qualify as a permanent facility for cooking? In my opinion it does, but the phrase “permanent facilities for cooking” is not defined, and the local electrical inspector should be consulted for his interpretation.
Q; Does a nonfused switch used as a disconnect for an outdoor air conditioning unit require working space that complies with 110.26?
A: Working space is required around all electrical equipment that is likely to require examination, servicing or maintenance while energized. Since it can reasonably be assumed that voltage measurements will be taken at this switch during troubleshooting, the required working space mentioned in 110.26(A)(1), Table 110.26(A)(1), and other parts of 110.26 must be provided.
Transfer switch for generator
Q: Are panelboards with interlocked main circuit breakers acceptable as transfer switches for optional standby generators?
A: Requirements for Optional Standby Systems are covered in Article 702, and 702.4 requires that all equipment must be designed and installed to prevent inadvertent interconnection of normal and alternate power sources in any operation of the transfer switch.
Some panelboard manufacturers produce panelboards that are suitable for this application. The 2005 edition of the General Information for Electrical Equipment Directory published by the UL provides guidance for selection of a manual transfer switch. Under the title Panelboards (QUEY) is this sentence: “Some panelboards constructed with interlocked main switching and overcurrent protective devices, have been investigated for use in optional standby systems in accordance with Article 702 of the NEC and are marked ‘Suitable for Use in accordance with Article 702 of the National Electrical Code ANSI/NFPA 70,’ or if provided within kit form, ‘Suitable for Use in accordance with Article 702 of the National Electrical Code ANSI/NFPA 70 when provided with interlock kit Cat No. __.’”
Optional standby generator size
Q: Does Article 702 of the NEC permit the connection of a 7.5 kVA, 120/240-volt single-phase generator to an automatic transfer switch that is also connected to a 100-ampere normal feeder that supplies a panelboard in a single-family dwelling?
A No. The transfer from the normal source to the generator will result in overloading of the generator and cause the generator overcurrent device to open. A manual transfer switch may be substituted for the automatic transfer switch with the occupant selecting the loads to be energized at one time. This is the most practical and economical method of connecting the generator to the premise wiring system. EC
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.