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312.8(B) Switch and Overcurrent Device

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Change Summary

  • Power monitoring equipment is now required to be listed for the application when installed in free spaces of cabinets and cutout boxes.
NEC® Text

312.8 Switch and Overcurrent Device Enclosures with Splices, Taps, and Feed-Through Conductors.
The wiring space within enclosures for switches and overcurrent devices shall be permitted for other wiring and equipment subject to limitations for specific equipment as provided in (A) and (B).

(A) Splices, Taps, and Feed-Through Conductors.
The wiring space of enclosures for switches or overcurrent devices shall be permitted for conductors feeding through, spliced, or tapping off to other enclosures, switches, or overcurrent devices where all of the following conditions are met:
(1) The total of all conductors installed at any cross section of the wiring space does not exceed 40 percent of the crosssectional area of that space.
(2) The total area of all conductors, splices, and taps installed at any cross section of the wiring space does not exceed 75 percent of the cross-sectional area of that space.
(3) A warning label complying with 110.21(B) is applied to the enclosure that identifies the closest disconnecting means for any feed-through conductors.
(B) Power Monitoring Equipment. The wiring space of enclosures for switches or overcurrent devices shall be permitted to contain power monitoring equipment where all of the following conditions are met:
(1) The power monitoring equipment is identified as a fieldinstallable accessory as part of the listed equipment, or is a listed kit evaluated for field installation in switch or overcurrent device enclosures.
(2) The total area of all conductors, splices, taps, and equipment at any cross section of the wiring space does not exceed 75 percent of the cross-sectional area of that space.

Copyright© 2016 National Fire Protection Association
(See NEC for complete text)

Expert Analysis

The wiring space within enclosures, such as a panelboard cabinet for switches or overcurrent devices, has been permitted to contain “other wiring and equipment” for a limited percentage (40% and 75%) of the cross-sectional area of the space as far back as the 1971 NEC. To answer the demand for such equipment being installed in a cabinet containing switches or overcurrent devices, the 2017 NEC adopted new text at 312.8(B) to allow power monitoring equipment with specific conditions. This additional text limits the inclusion of devices and equipment in a wiring space to power monitoring equipment that is identified as field-installable accessories as part of the listed equipment, or as a listed kit evaluated for field installation in the specific equipment. This new wording also retains the limit on the amount of space occupied by all conductors, splices, taps, devices, and equipment to the same 75 percent fill requirement previously located at 312.8(2) [now 312.8(A)(2)].

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