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Electrical Contractors

NEC Questions 3/25/2003

By Mike Holt for EC&M Magazine

Q1. Regarding 70V distributed sound systems, when is the wiring of such a system required to be in a raceway? My interpretation, based on Article 725, is that if the amplifier output exceeds 100W, the wiring is classified as a Class 1 Remote-Control and Signaling Circuit it is required to be installed in a Chapter 3 wiring method.

A1. The output wiring method for sound systems shall be as marked on the amplifier [640.9(C)], which is typically "Class 2 Wiring." Class 2 wiring is not required to be installed in a raceway, but it must be installed in accordance with Article 725. However, Class 2 cables installed in air-handling spaces, such as above a suspended ceiling used for environmental air, shall be either plenum rated or they shall be installed in a metal raceway [725.61].

Q2. When can Electrical Nonmetallic Tubing (ENT) be stubbed out in a drop ceiling? The building in question is 3 stories and the ceiling in the hallway is regular T-bar.

A2. ENT is permitted exposed in wall, floors and ceiling (including suspended ceilings) in buildings not exceeding three stories [362.10(1)(a) and 362.10(5).

However, in building exceeding three stories, ENT is only permitted to be installed concealed within walls, floors, and ceilings where the walls, floors, and ceilings that provide a thermal barrier having at least a 15-minute finish rating [362.10(2)].

ENT is permitted above a suspended ceiling in building exceeding three stories if the suspended ceiling provides a thermal barrier having a 15-minute finish rating [362.10(5)].

Exceptions to the two above rules permit ENT exposed in building (including above suspended ceilings) where a fire sprinkler system is installed in the building in accordance with NFPA 13-1999 Standard for the Installation of Sprinkler Systems.

Q3. I was told by an inspector that 3-way or 4-way switches are required in rooms having more than one entry or exit. I haven't been able to document this anywhere in the code.

A3. The NEC does not specify the switch location for room lighting outlets nor does it require 3- or 4-way switches to accommodate more multiple room entries or exits. This is an issue that is left to the designer, not the electrical inspector.

Q4. I understand there is a provision in the Code prohibiting the "daisy-chain" feed-through connections of conductors on receptacles and switches. In other words, all wiring at receptacles and switches must be pigtailed. The intention was that the removal of a wiring device was not to interrupt the continuity of the circuit involved. Is there such a rule?

A4. No, but in multiwire branch circuits, the removal of a wiring device, such as a receptacle, shall not interrupt the continuity for the grounded (neutral) conductor [300.13(B)]. Therefore, the grounded (neutral) conductors shall be spliced together and a pigtail shall be provided for device terminations.

The opening of the ungrounded (hot) or grounded (neutral) conductor of a two-wire circuit during the replacement of a device does not cause a safety hazard, so pigtailing of these conductors is not required by the NEC.

Note: If the continuity of the grounded (neutral) conductor of a multiwire circuit is interrupted (open), there could be a fire and/or destruction to electrical equipment because of over or under voltage.

Q5. Is the branch circuit wiring for smoke detectors located in dwelling unit bedrooms required to be AFCI protected?

A5. All branch circuits supplying 15A or 20A, single-phase, 125V outlets installed in dwelling unit bedrooms shall be AFCI protected by a device that is listed to protect the entire circuit from an arc fault. Therefore, AFCI protection is required for the branch circuit wiring for smoke detector outlets.

Note: The Canadian Electrical Code does not permit the smoke detector to be GFCI or AFCI protected.

Q6. Due to space constrictions, I installed a 45 KVA transformer above a suspended ceiling used for environmental air. The installation is in accordance with the requirements contained in 450.13(B), which specifies that dry-type transformers not exceeding 50 kVA shall be permitted in hollow spaces of buildings not permanently closed in by structure.

The electrical inspector rejected the installation because the transformer was not listed for use in the environment air space (plenum rating). I looked in the UL Green Book and can't find a transformer classification for this condition. Does the NEC require transformers installed in environmental air spaces to be listed for plenum applications?

A6. No, the NEC does not require transformers to be plenum rated or listed for use in an environmental air space, they just need to be in a metal enclosure (ventilated or nonventilated) [300.22(C)(2)]. For more information, review the NEC Handbook comments to 450.13(B), page 578.

Q7. How much working space is required between a 120/208V distribution panel and a 277/480 transformer on the opposite side of the room?

A7. The working space requirement contained in 110.26 only applies to equipment that is likely to require examination, adjustment, servicing, or maintenance while energized [110.26]. This is a judgment call by the Authority Having Jurisdiction (AHJ), I personally would require the working space be a minimum of 4 ft deep by 30 in wide in accordance with 110.26(A)(1) and (A)(2).

Depth 110.26(A)(1). The depth of the working space is measured from the enclosure front and it shall not be less than the following:

Nominal Voltage to Ground Condition 1 Condition 2 Condition 3
0-150 3 ft 3 ft 3 ft
151-600 3 ft 3.5 ft 4 ft

Condition 1 - Exposed live parts on one side and no live or grounded parts on the other side of the working space.

Condition 2 - Exposed live parts on one side and grounded parts on the other side of the working space. For the purpose of this table, concrete, brick, or tile walls are considered as grounded.

Condition 3 - Exposed live parts on both sides of the working space.

Width 110.26 (A)(2). The working space shall be a minimum of 30 in. wide, but in no case less than the width of the equipment. In all cases the working space shall be of sufficient width, depth, and height to permit at least a 90 opening of all equipment doors.

Q8. The majority of information technology circuits (wiring under raised floors of data process equipment rooms) I've come across are not secured in place; they are laid under the raised floor in liquidtight conduit. Is this practice allowed by NEC?

A8. No. Branch circuit conductors within a raised floor shall be securely fastened in place in accordance with 300.11 [645.5(D)(2)]. However, power cables and associated boxes, connectors, plug, and receptacles listed as part of information technology equipment are not required to be secured in place [645.5(E)].

Q9. We have been purchasing power whips made from liquidtight conduit with boxes that are listed for use with information technology equipment. We do this to get away from the requirement that requires the liquidtight to be secured in place. We have not run into any problems yet, but I thought I would run it past you and see what you think.

A9. Because the wiring method is listed as part of information technology equipment, it is not required to be secured in place [645.5(E)].

Note: I didn't know there was such a product listed for this purpose.

Q10. Does the NEC require all receptacles downstream from a GFCI receptacle be marked "GFCI protected"? I thought I read this somewhere in the NEC.

A10. "GFCI Protected" marking is only required where a nongrounding-type receptacle has been replaced with a grounding-type receptacle that is GFCI protected in a location where no grounding means exists in the outlet box. Under this condition, all of the grounding type receptacle shall be marked "GFCI Protected No Equipment Ground."

Note: GFCI protection functions properly on a 2-wire circuit without an equipment grounding conductor.