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Code Quandaries

Jul 1, 2001 12:00 PM, By Mike Holt, NEC Consultant

At EC&M, we know NEC issues are very important to our readers. That's why we've dedicated a monthly department to answering your latest Code questions and concerns. When you find yourself stumped by the Code, just e-mail your question to the author at mike@mikeholt.com for future consideration in Code Quandaries.

Q. Can I connect the 120V receptacles in a store to the same branch-circuit that supplies the lights?

A. Yes. Receptacles and lights can be on the same circuit. Sec. 210-23(a) states that a 15A or 20A branch-circuit can supply lighting units or other utilization equipment, or a combination of both. The rating of one piece of cord-utilization equipment shall not exceed 80% of the branch-circuit ampere rating, and the total rating of utilization equipment fastened in place (other than lighting fixtures) shall not exceed 50% of the branch-circuit ampere rating where lighting units are also supplied.

Q. Is it legal to use nonmetallic sheath cable (NM) or armored cable (AC) in a volunteer fire hall?

A. Yes. You can install both NM and AC cables in accordance with the NEC requirements for the wiring method. See Art. 333 for armored cable and Art. 336 for nonmetallic sheath cable.

Q. Do I need a bonding bushing or bonding locknut for service raceways that enter a standard knockout without concentric and eccentric rings?

A. Yes. Sec. 250-92 specifies you must bond all service raceways that contain unprotected service conductors in accordance with Sec. 250-94. The latter section requires you to ensure the electrical continuity of service raceways by using bonding-type locknuts or bushings. Standard locknuts or bushings shall not be the means for the bonding required by this section. Only one end of a service raceway must be bonded in accordance with the requirements of Sec. 250-94.

Q. What is the maximum cord length for a portable tool?

A. There is no maximum length. According to UL 45 Standard for Portable Electric Tools, the cord length must be a minimum of 6 ft. So, manufacturers can build portable electric tools with a 25-ft to 30-ft cord if they desire.

Q. Can I install a dry-type transformer (45kVA, 480V) above a suspended 2×4 lay-in-grid ceiling?

A. Yes. Sec. 450-13 requires you to make all transformers readily accessible to qualified personnel for inspection and maintenance. But subsection (b) states that dry-type transformers 600V, nominal, or less and not exceeding 50kVA can be located in hollow spaces of buildings not permanently closed in by the structure. Those spaces must meet the ventilation requirements of Sec. 450-9, and they must be separated from combustible materials per Sec. 450-21(a).

Sec. 450-13(b) continues to permit the installation of dry-type transformers rated 600V or less and not exceeding 50kVA in hollow spaces of hung ceiling areas, provided these spaces are fire-resistant, ventilated, and accessible. According to Sec. 300-22(c)(2), you can install transformers in hollow spaces where the space is used for environmental air, provided the transformer is in a metal enclosure (ventilated or nonventilated) and suitable for the ambient air temperature within the hollow space. The requirement of Sec. 450-13(b) applies to transformer installations in “other spaces used for environmental air.”

Q. What are the restrictions on installing electrical wiring and fixtures in trees?

A. The NEC has two rules on this issue.

• Sec. 225-26 states, “vegetation such as trees shall not be used for support of overhead conductor spans.”

• Sec. 410-16(h) states “outdoor lighting fixtures and associated equipment shall be permitted to be supported by trees.”

So you can install outdoor lighting fixtures in and on trees, but the wiring to these fixtures must be run underground.

Q. I'm using interlocked MC cable for the branch-circuit wiring of ceiling fixtures located above 7½ ft in the patient care area of a dental office. The local inspector says I can't use interlocking MC cable because the cable sheath assembly does not qualify as an equipment-ground return path. The MC cable contains an insulated copper equipment-grounding conductor. Is the inspector right?

A. Yes. Sec. 517-13(b) specifies that all branch-circuits serving patient care areas, such as medical offices, must be installed in “a metal raceway or a cable assembly that qualifies as an equipment grounding return path.” According to UL, the outer sheath of an interlocked MC cable assembly is not listed and identified for grounding, therefore it does not qualify as an equipment grounding return path. The fact that MC cable contains an insulated copper equipment grounding conductor does not relieve you from the obligation of installing the circuit conductors in a metal raceway or a cable assembly that qualifies as an equipment grounding return path. Changes to this section in the 2002 NEC will make this issue clearer.

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