Stumped by the Code?
Q. As an engineer, I was taught that good wiring practices meant keeping the phase circuit conductors and control conductors (120V) separated. I agree that in many circumstances that's the ideal condition, but what does the NEC require?
A. The NEC permits Class 1 remote and power supply circuit conductors to occupy the same cable, enclosure, or raceway, but only where the equipment powered is functionally associated with the conductors [725.26(B)(1)] (Fig. 1 below.)
Q. There's an ongoing practice among electrical contractors in my area to connect a short piece of 14 AWG wire to the 12 AWG in a receptacle box to facilitate the use of the push-in connectors on the back of 15A receptacles installed on a 20A circuit. When I ask how this could be permitted, they cite the fact that the device is rated 15A and that therefore the practice is allowed according to the branch-circuit tap rules. Is this true?
A. No. The minimum size conductor for a 20A circuit is 12 AWG [240.4(D)], and a 15A duplex receptacle is permitted on a 20A circuit [Table 210.21(B)(3)]. Also, 210.19(A)(4) Ex. 1(c) doesn't permit 15A tap (14 AWG) conductors for a receptacle outlet on a 20A circuit.
Q. I work in a chemical laboratory and have been trying to get GFCI-protected outlets installed in the vicinity of any apparatus that uses running water (for cooling, for instance). I finally managed to convince my management to do it, but then when the electrician came, he insisted that it isn't necessary. Who's right?
A. The electrician's correct on this one. In commercial and industrial occupancies, GFCI protection is only required for receptacles in bathrooms, rooftops, and kitchens [210.8(B)].
Q. We put out a drawing with a detail showing the removal of the tabs on a 20A, 125V duplex receptacle, thus creating two single 20A devices. A separate 20A circuit supplies each receptacle, but the inspector rejected the installation, citing that it's against the Code. Is the inspector right?
A. Your design is fine. Each receptacle is individually rated 20A, 125V, so there's no problem. But where more than one branch circuit supplies more than one receptacle on the same yoke, a means to simultaneously disconnect the ungrounded conductors that supply those receptacles shall be provided at the panelboard where the branch circuits originated [210.7(C)].
Q. The NEC requires receptacle outlets to be located so no point measured horizontally along the floor line in any wall space is more than 6 feet from a receptacle outlet. Is there a similar requirement for receptacles in a commercial occupancy?
A. The NEC doesn't require receptacle outlets in the wall space of commercial or industrial occupancies. Simply locate receptacles per the plan.
Q. Can low-voltage and limited-energy cables be installed within an enclosure with power conductors?
A. Low-voltage and limited-energy conductors can be installed with power conductors in an enclosure, but only where the power circuit conductors are introduced solely to connect to the low-voltage or limited-energy equipment. In addition, a minimum of 0.25 inches of separation shall be maintained between the low-voltage and limited-energy conductors and power conductors [725.55(D)].
Q. What is the maximum run length permitted for flexible metal conduit?
A. Except for flexible nonmetallic conduit [356.12(3)], the NEC doesn't limit the length of any raceway of 0.5-inch trade size or larger. When using tap conductors in accordance with 410.67(C), the raceway length is limited to 6 feet.
Q. I would like your thoughts on a situation where my inspector is requiring the rebar within a building's footing to be bonded to the service grounding electrode. Sec. 250.50 indicates that if this item is available on the premises, then it's to be bonded so that it's part of the building's grounding electrode system. What if the concrete has already been poured? I remember reading somewhere that the NEC doesn't require the concrete to be chipped out to gain access to the footing steel. It seems that chipping out the footing creates other problems, and other reasonable methods are available to establish an earth ground.
A. Many inspections consider the concrete-encased electrode “available” unless there's no rebar in the foundation or footers. In addition, if it's shown on the drawings but not left accessible by the general contractor (GC), then it's the GC's responsibility to correct this construction error (Fig. 2).
Note: The 2005 NEC is likely to require the footing rebar to be used as part of the grounding electrode system in new buildings or structures.
Q. Two electricians told me that a disconnecting means is required within sight of a transformer if it's installed above a dropped ceiling. My problem with locating a disconnect in this space is the fact that I'd have to work around ductwork and pipes. Are they right?
A. No, a disconnecting means need not be installed within sight of a transformer.
Q. Can a GFCI receptacle be installed on an AFCI-protected circuit?
A. The NEC requires all equipment to be installed and used in accordance with any instructions included in the listing or labeling. There are no product restrictions on placing a GFCI receptacle on an AFCI-protected circuit. In addition, the devices shouldn't disturb each other. So yes, this is permitted.
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