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Figure 01
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For EC&M Magazine
By Mike Holt, NEC® Consultant
Here's the follow-up to yesterday's newsletter.
This includes the answers to the questions sent, so you can see how you did.
Note: The answers to these questions are based on the 2017 NEC.
Underlined text indicates a change in the rule for the 2017 NEC.
Q1. When overcurrent protection device enclosures contain splices, taps, and feed-through conductors, what are the NEC requirements?
A1. Cabinets are permitted to contain overcurrent protection devices and other wiring and equipment as provided in 312.8(A) and (B).
(A) Splices, Taps, and Feed Through Conductors. The wiring space within cabinets can be used for conductors feeding through, spliced, or tapping where all of the following conditions are met:
(1) The area of all conductors at any cross section doesn't exceed 40 percent of the cross sectional area of the space.
(2) The area of conductors, splices, and taps installed at any cross section doesn't exceed 75 percent of the cross sectional area of that space. Š
Author's Comment:
The 40 and 75 percent requirement applies to all conductors, all splices, and all taps within the cross-sectional area, not just the added conductors, splice(s), or tap(s).
(3) A permanently affixed warning label having sufficient durability to withstand the environment involved and comply with 110.21(B), must be applied on the cabinet to identify the location of the disconnecting means for the feed through conductors. Figure 01
(B) Power Monitoring Equipment. The wiring space within cabinets can contain power monitoring equipment where all of the following conditions are met:
(1) The power monitoring equipment is identified as a field installable accessory as part of listed equipment, or a listed kit for field installation in the overcurrent protection device enclosures.
(2) The area of all conductors, splices, taps, and equipment at any cross section doesn't exceed 75 percent of the cross sectional area of that space.
Q2. What is the Code rule regarding the installation of surface extensions from a box or box cover?
A2. Surface extensions can only be made from an extension ring installed over a box [314.22]. Š
Ex: A surface extension can be made from the cover of a box if the cover is designed so it's unlikely to fall off if the mounting screws become loose. The surface extension wiring method must be flexible to permit the removal of the cover and provide access to the box interior, and equipment grounding continuity must be independent of the connection between the box and the cover.
Q3. What are the Code rules for allowable support means of boxes and conduit bodies?
A3. Boxes can be fastened to any surface that provides adequate support [314.23(A)].
Boxes can be supported from any structural member, or they can be supported from grade by a metal, plastic, or wood brace [314.23(B)]. Š
Nails or screws used as a fastening means, must secure boxes by using outside brackets or by using mounting holes in the back or in a single side of the box, or pass through the interior within 14 in. of the back or ends of the box. Screws aren't permitted to pass through the box unless the exposed threads in the box are protected using approved means to avoid abrasion of conductor insulation. Mounting holes made in the field to support boxes must be approved by the authority having jurisdiction [314.23(B)(1)].
Metal braces no less than 0.02 in. thick and wood braces not less than a nominal 1 in. × 2 in. can support a box [314.23(B)(2)].
Boxes can be secured to a finished surface (drywall or plaster walls, or ceilings) by clamps, anchors, or fittings identified for the purpose [314.23(C)]. Š
Outlet boxes 100 cu in. or less can be supported to the structural or supporting elements of a suspended ceiling, if securely fastened by any of the following methods [314.23(D)]:
(1) Ceiling Framing Members. An outlet box can be secured to suspended ceiling framing members by bolts, screws, rivets, clips, or other means identified for the suspended ceiling framing member(s). Š
Author's Comment:
• If framing members of suspended ceiling systems are used to support luminaires, they must be securely fastened to each other and must be securely attached to the building structure at appropriate intervals. In addition, luminaires must be attached to the suspended ceiling framing members with screws, bolts, rivets, or clips listed and identified for such use [410.36(B)].
(2) Independent Support Wires. Outlet boxes can be secured with identified fittings to the ceiling support wires. If independent support wires are used for outlet box support, they must be taunt and secured at both ends [300.11(B)]. Š
Author's Comment:
• See 300.11(B) on the use of independent support wires to support raceways and cables.
Raceway”Supported Boxes and Conduit Bodies Without Devices or Luminaires. Two intermediate metal or rigid metal conduits, threaded wrenchtight into the enclosure, can be used to support an outlet box that doesn't contain a device or luminaire, if each raceway is supported within 36 in. of the box or within 18 in. of the box if all conduit entries are on the same side [314.23(E)]. Š
Ex: Conduit bodies are permitted to be supported by any of the following wiring methods: Š
(1) Intermediate metal conduit, Type IMC©
(2) Rigid metal conduit, Type RMC
(3) Rigid polyvinyl chloride conduit, Type PVC
(4) Reinforced thermosetting resin conduit, Type RTRC
(5) Electrical metallic tubing, Type EMT
Raceways”Boxes and Conduit Bodies with Devices or Luminaires. Two intermediate metal or rigid metal conduits, threaded wrenchtight into the enclosure, can be used to support an outlet box containing devices or luminaires, if each raceway is supported within 18 in. of the box [314.23(F)].
Pendant Boxes containing a hub can be supported from a flexible cord connected to fittings that prevent tension from being transmitted to joints or terminals [314.23(H)(1) and 400.10].
Q4. What does the NEC require regarding outlet boxes intended to support ceiling paddle fans?
A4. Outlet boxes for a ceiling paddle fan must be listed and marked as suitable for the purpose, and must not support a fan weighing more than 70 lb. Outlet boxes for a ceiling paddle fan that weighs more than 35 lb must include the maximum weight to be supported in the required marking [314.27(C)]. Š
Author's Comment:
• If the maximum weight isn't marked on the box, and the fan weighs over 35 lb, it must be supported independently of the outlet box. Ceiling paddle fans over 70 lb must be supported independently of the outlet box. Š
Where spare, separately switched, ungrounded conductors are provided to a ceiling mounted outlet box, in a location acceptable for a ceiling suspended (paddle) fan in one family, two family, or multifamily dwellings, the outlet box or outlet box system must be listed for the support of a ceiling suspended (paddle) fan. Š
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