2017 NEC: Conductors, Switches, Receptacles—Significant Changes in the 2017 NEC, Part 5

By Michael Johnston | Dec 15, 2016




This article reviews changes in Chapter 3, Wiring and Methods and Materials, and Chapter 4, Equipment for General Use, in the 2017 edition of the National Electrical Code (NEC).
 Visit for this full series.

336.10 Uses Permitted

New list item (9) in 336.10 permits type TC-ER cable containing both power and control conductors to be used in one- and two-family dwelling units. In these installations, type TC-ER cable must be additionally marked “JP” to identify it as suitable for pulling through structural members. An exception permits the use of TC-ER cable for generators and associated equipment without the need to apply ampacity correction factors in accordance with 334.80 or 340.80.

338.10(B) Branch Circuits 
and Feeders

Type SE cable with ungrounded conductor sizes 10 AWG and smaller, installed in thermal insulation, is limited to ampacity rating at 60°C. Larger SE cable installed in thermal insulation is no longer limited to an ampacity in the 60°C and can be applied at 75°C rating.

358.10 Uses Permitted

Section 358.10 has been revised for clarity and consistency with other .10 sections covering uses permitted for raceways. Permissive applications for EMT in 358.12 are relocated in 358.10 for clarity. Section 358.10(B) now addresses stainless steel EMT for corrosive environments.

366.20, 368.20, 376.20 and 378.20 Conductors Connected in Parallel

New requirements for conductors connected in parallel are added in the .20 section of articles 366, 368, 376 and 378. Alternating current (AC) circuits connected in parallel must have conductors installed in groups consisting of not more than one conductor per phase, neutral or grounded conductor. The intention is to prevent current imbalance that can create heat and subsequent failure in the paralleled conductors due to inductive reactance.

392.22(A) Number of Multiconductor Cables, Rated 2000 Volts or Less, in Cable Trays

Each section of cable tray containing dividers must be treated individually with respect to fill calculations. A ladder-type tray that is divided with power on one side and control on the other side may now have the fill calculated by both 392.22(A)(1) and (A)(2) permitting a 50 percent fill calculation on the signal side of the tray.

Article 400—Flexible Cords 
and Cables

404.2(C) Switches Controlling Lighting Loads

The reference to “habitable room” has been deleted. Bathrooms, hallways, stairways and rooms suitable for human habitation require the grounded conductor to be installed. A reference to the applicable building code has been included. The section parent text has been modified for clarity, for multiple switch locations. New text requires connection to switch devices (where required) beginning Jan. 1, 2020. New Section 404.22 has been added and correlates with this section.

404.22 Electronic Lighting 
Control Switches

All electronic lighting control switches are required to be listed. As of Jan. 1, 2020, electronic lighting control switches (with exceptions) will not be permitted to introduce current on the equipment-grounding conductor during normal operation. Manufacturers will only make devices that place current on the equipment-grounding conductor during normal operation for replacement/retrofit.

406.2 Outlet Box Hood

Section 406.2 now contains a definition for “Outlet Box Hood” that applies where the term is used within Article 406. The hood does not serve to complete the electrical enclosure; it reduces the risk of water coming in contact with electrical components. Outlet box hoods are commonly known as a “bubble cover” or “in-use cover.”

406.3(F) Receptacles with 
USB Charger

New 406.3(F), Receptacles with USB Charger, permits these devices to be installed if they are listed and constructed so the Class 2 circuitry is integral with the receptacle. These devices are listed to ANSI/UL 498.

406.12 Tamper-Resistant Receptacles

Section 406.12 now addresses all 125- and 250V, nonlocking-type, 15- and 20-ampere receptacles. New occupancies have been added to the receptacle tamper-resistant requirements: Preschools and elementary education; business offices; corridors; waiting rooms and the like in clinics, medical and dental offices and outpatient facilities; assembly occupancies described in Section 518.2; and dormitories.

For more information and to view all of the proposed revisions, please visit

About The Author

A man, Mike Johnston, in front of a gray background.

Michael Johnston

NECA Executive Director of Codes and Standards

JOHNSTON is NECA’s executive director of codes and standards. He is a member of the NEC Correlating Committee, NFPA Standards Council, IBEW, UL Electrical Council and NFPA’s Electrical Section. Reach him at [email protected].






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