Ecmweb 22787 Nec Code Quandaries 1118 Pr 0
Ecmweb 22787 Nec Code Quandaries 1118 Pr 0
Ecmweb 22787 Nec Code Quandaries 1118 Pr 0
Ecmweb 22787 Nec Code Quandaries 1118 Pr 0
Ecmweb 22787 Nec Code Quandaries 1118 Pr 0

Stumped by the Code? Requirements for Overcurrent Protection Device Enclosures

Nov. 16, 2018
NEC Code Quandaries

All questions and answers are based on the 2017 NEC.

Underlined text indicates a Code change.

Q. When overcurrent protection device enclosures contain splices, taps, and feed-through conductors, what are the NEC requirements?

A. Cabinets are permitted to contain overcurrent protection devices and other wiring and equipment as provided in Sec. 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 the following conditions are met:

(1) The area of all conductors at any cross section doesn’t exceed 40% 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% of the cross‑sectional area of that space. Note: The 40% and 75% 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 Sec. 110.21(B) must be applied on the cabinet to identify the location of the disconnecting means for the feed‑through conductors (Figure).

(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% of the cross‑sectional area of that space.

Q. What uses are not permitted by the Code for metal wireways?

A. Metal wireways are not permitted [Sec. 376.12]:

(1) Where subject to severe physical damage

(2) Where subject to corrosive environments.

Q. What uses are permitted by the Code for metal wireways?

A. Metal wireways are permitted [Sec. 376.10]:

(1) Exposed.

(2) In any hazardous locations, as permitted by other articles in the Code.

(3) In wet locations where listed for the purpose.

(4) Unbroken through walls, partitions, and floors.

See Sec. 501.10(B), Sec. 502.10(B), and Sec. 504.20 for metal wireways used in hazardous locations.

Q. What does the NEC require when conductors connected in parallel are installed in metal wireways?

A. Where conductors are installed in parallel as permitted in Sec. 310.10(H), the parallel conductor sets must be installed in groups consisting of not more than one conductor per phase or neutral conductor to prevent current imbalance in the paralleled conductors due to inductive reactance. [Sec. 376.20]

Q. What is the maximum size conductor that the Code allows to be installed in a wireway?

A. The maximum size conductor permitted in a wireway isn’t permitted to be larger than that for which the wireway is designed [Sec. 376.21].

About the Author

Mike Holt

Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.

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