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By Mike Holt for EC&M Magazine
Q1. As an engineer, we were taught that good wiring practices meant keeping the phase circuit conductors and control conductors (120V) separated. I agree that in many circumstances that this is an ideal condition, but what does the NEC required?
A1. 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).
Q2. There is an on going practice among electrical contractors in my area to connect a short piece of 14 AWG wire to the 12 AWG in a receptacle box. The purpose of this is to facilitate the use of the push in connectors on the back 15A receptacles on a 20A circuit. When I ask how is this permitted? They cite the fact that the device is rated 15A and therefore this practice is allowed according to the branch-circuit tap rules. Is this true?
A2. No. The minimum size conductor for
a 20A circuit is 12 AWG [240.4(D)] and Table 210.21(B)(3) permits a 15A duplex receptacle
on a 20A circuit.
A3. The electrician's correct on this one. In commercial and industrial occupancies, GFCI protection is only required for receptacles in bathroom, rooftops, and kitchens [210.8(B)].
Q4. Can a GFCI receptacle be installed on an AFCI protected circuit?
A4. The NEC requires all equipment to
be installed and used in accordance with any instructions included in the listing or labeling,
and there are no product restrictions on placing a GFCI receptacle on an AFCI protected
circuit. In addition, neither device should cause any disturbance of the other. So yes
this is permitted.
Q6. 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?
A6. Your design is fine, each receptacle is individually rated 20A, 125V, so there is 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 supplying those receptacles shall be provided at the panelboard where the branch circuits originated [210.7(C)].
Q7. The NEC requires receptacle outlets to be located so that no point measured horizontally along the floor line in any wall space is more than 6 ft from a receptacle outlet. Is there a similar requirement for receptacles in a commercial occupancy?
A7. The NEC does not require receptacles outlets in the wall space of commercial or industrial occupancies. Simply locate receptacles per the plan.
Q8. Can I run a three-phase circuit in the same raceway with a single-phase circuit?
A8. Yes, as long as the conductor insulation is suitable for the maximum circuit voltage applied to any conductor within the raceway [300.3(C)(1)].
Q9. What is the maximum run length permitted for flexible metal conduit?
A9. Except for flexible nonmetallic conduit [356.12(3)], the NEC does not limit the length of any raceway of 0.50 inch trade size or larger.
Q10. Can low-voltage and limited-energy cables be installed within an enclosure with power conductors?
A10. 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 in. separation shall be maintained between the low-voltage and limited-energy conductors and power conductors [725.55(D)].
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