Article 100—Definitions; Article 210—Branch Circuits; Article 250—Grounding and Bonding; Article 334—Nonmetallic-Sheathed Cable: Types NM, NMC, NMS; Article 422—Appliances; Article 680—Swimming Pools, Fountains, and Similar Installations; The 2007 Guide Information for Electrical Equipment Directory (White Book) also is mentioned.
Multiwire branch-circuit disconnects
Where three-phase, 120/208-volt branch circuits supply receptacles and lighting in a drugstore, are handle ties or common trip circuit breakers required for these multiwire branch circuits?
It depends on which edition of the National Electrical Code (NEC) is being enforced in your jurisdiction. The answer is no if you are operating under the 2005 edition of the NEC. However, a disconnecting means must be provided internal or external to fluorescent luminaires that contain double-ended lamps and can be serviced in place. This disconnecting means must open both conductors, and the line side conductors must be guarded (see 410.73(G) in the 2005 edition).
A change in the 2008 edition of the NEC in 210.4(B) requires handle ties or multipole circuit breakers on all multiwire branch circuits. The change reads: “210.4(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.”
A number of proposals were submitted to require simultaneous disconnection of all ungrounded branch-circuit conductors from the source for multiwire branch circuits. The substantiation for one included an electrocution of an electrician on a multiwire branch circuit when the neutral conductors were separated and one ungrounded conductor was deenergized.
Deep fryer disconnect
Is a “within sight” disconnect switch required for a 6,000-watt, 240-volt, single-phase deep fryer? The unit is cord-and-plug connected.
The cord-and-plug connection must be accessible if it is to serve as a disconnecting means for the appliance. This permission is granted by 422.33(A). If the cord-and-plug connection is not accessible, a disconnecting means must be provided within sight (visible and not more than 50 feet from the deep fryer), or the disconnecting means must be capable of being locked in the off position. The provisions for adding a lock must be installed at the disconnect and remain in place regardless of whether a lock is installed. This requirement is in 422.31(B).
Nonmetallic sheathed cable use
Is 18 inches of nonmetallic sheathed cable acceptable as a wiring method from a junction box to a garbage disposer where the non-metallic sheathed cable is taped to the drainpipe on the sink for support?
Hardware suitable for securing and supporting nonmetallic sheathed cable is mentioned in 334.30, and tape is not mentioned. Support hardware includes staples, cable ties, straps, hangers and similar fittings.
Also, the cable is probably subject to physical damage and may be exposed to excessive temperatures when hot water is discharged from the sink. Because of these requirements and possibilities of other problems, the answer is no, nonmetallic sheathed cable cannot be taped to the drain pipe.
Two appliances on a branch circuit
Does the NEC permit the installation of a dishwasher and garbage disposer on the same 20-ampere branch circuit?
The answer depends on the ampere ratings of each appliance. Where each appliance has a full load current of 10 amperes or less, they both can be supplied by a 20-ampere branch circuit. This is permitted by 210.23(B)(2), which allows two appliances fastened in place to be supplied by a 20-ampere branch circuit where the full-load current of each does not exceed 50 percent of the branch circuit rating.
Where the size of the service-drop conductors is increased because of voltage drop, is it necessary to increase the size of the grounding-electrode conductor at the service?
No, the grounding-electrode conductor does not have to be increased in size because the service-drop conductors were increased in size to reduce voltage drop.
Service-drop conductors are described in Article 100—Definitions as: “The overhead service conductors from the last pole or other aerial support to and including the splices, if any, connecting to the service-entrance at the building or other structure.” The definition of service-entrance conductors is: “Service-Entrance Conductors, Overhead System. The service conductors between the terminals of the service equipment and a point usually outside the building, clear of building walls, where joined by tap or splice to the service drop.”
Notice that the title for the table 250.66 “Grounding Electrode Conductor for Alternating Current Systems” contains one column with the title “Size of Largest Ungrounded Service-Entrance Conductor or Equivalent Area for Parallel Conductors.” Since the term “service-entrance” is used, the grounding--electrode conductor does not have to be increased where only the service-drop conductors are increased.
What was the reason for removing the ground-fault circuit interrupter exceptions to 210.8(A)(2)?
A few proposals were submitted to revise 210.8 for the 2008 edition of the NEC. Some that Code-Making Panel Number 2 accepted removed the exceptions to 210.8(A)(2) and 210.8(A)(5). The exceptions to 210.8(A)(2) that eliminated receptacles that are not readily accessible and receptacles that supplied appliances located within dedicated space were removed. These same two exceptions also were removed from 210.8(A)(5), which covered receptacles in unfinished basements. More than one proposal to delete the exceptions were made, and the Code-Making Panel accepted several to arrive at the final language that appears in the 2008 edition. Here is the substantiation that was submitted by one of the proposers whose proposal was accepted: “Substantiation. The change in 210.8(A)(7) in the 2005 edition has created a contradiction. If a laundry or utility sink is present in a garage or basement and a clothes washer receptacle is within 6 feet of that sink, it now requires GFCI protection. The existing exceptions are no longer necessary. The present generation of GFCI devices do not have the problems of ‘nuisance tripping’ that plagued the earlier devices.”
Other proposals that recommended removal of the exceptions pointed out that the product standard for cord-and-plug-connected electrical equipment was changed to a maximum of 0.5 milliampere of leakage current. For an appliance to trip a GFCI, leakage current would have to increase 8 to 12 times the permitted leakage current of the products. It also was pointed out that the appliance surface is the shock hazard, not the receptacle.
Bonding service raceway
Is it necessary to bond both ends of electrical metallic tubing that connects the meter socket to the service-disconnecting means? The voltage is 208Y/120, three-phase.
Bonding of the electrical metallic tubing is required by 250.92(B). Four methods are listed. Other sections that require bonding of the metal raceway are 250.4 and 250.8. One end of the electrical metallic tubing has to be bonded to ensure a low-impedance ground-fault current path.
20A branch-circuits receptacles
I have a job to install two 20-ampere duplex receptacles on a 25-ampere branch circuit for two lottery vending machines. The lottery commission has supplied the above information and has suggested 10 AWG copper branch circuit conductors. Will this be a -Code-compliant installation?
No. It will not. Either the receptacles will have to have a 30-ampere rating, or the overcurrent protective device will have to be changed to 20 amperes. But before making any changes, talk to someone with the lottery commission to get the ampere ratings of the lottery machines.
A 25-ampere multioutlet branch circuit is not listed in 210.23 and 210.24, but a 20-ampere receptacle should not be installed on a circuit protected by a 25-ampere overcurrent device. Tables 210.21(B)(3) and 210.24 list 30-ampere receptacles as the minimum ampere rating for these devices on 30-ampere branch circuits.
If the lottery vending machines have full load currents that do not exceed 16 amperes, the conductor size can be changed to 12 AWG copper and overcurrent protection reduced to 20 amperes. If the full load current exceeds 16 amperes, receptacles will have to be increased to 30 amperes.
Underground wiring near pool
Does the Code permit underground wiring not associated with an in-ground swimming pool within 5 feet of the pool wall?
Generally all underground wiring must be located at least 5 feet from the walls of a swimming pool if it does not supply loads associated with the pool. However, where limitations do not allow 5 feet of clearance from the pool, complete raceway systems are allowed. Wiring methods are limited to rigid metal conduit, intermediate metal conduit or nonmetallic raceways. Metal raceways must be corrosion-resistant and suitable for the location. The minimum burial depth for this wiring is 6 inches for rigid metal conduit and intermediate metal conduit and 18 inches for nonmetallic conduit.
Ground rod diameter
Does the Code allow 0.5-inch diameter by 8-feet-long grounding electrodes for electric services?
Yes. The minimum diameter of a ground rod is 0.5 inch. This size is permitted by 250.52(A)(5)(8) and reads, “Grounding electrodes of stainless steel and copper or zinc coated steel shall be at least 15.87 mm (five-eighths in.) in diameter, unless listed and not less than 12.70 mm (0.5 in.) in diameter.”
According to 2007 edition of the White Book, “Ground rods are solid copper, solid stainless steel, copper-jacketed steel, stainless-steel jacketed, galvanized steel, and chemically charged. They are not less than 0.5 inch diameter and not less than 8 ft. long and capable of being driven to a depth of 8 ft.”
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.