Wiring Methods and Materials

By Michael Johnston | Oct 15, 2019
Copper wiring.




Part 5 of this series focuses on revisions in Chapter 3 of the 2020 NEC, “Wiring Methods and Materials,” which covers the general requirements for wiring and the requirements specific to each wiring method, such as electrical conduit and tubing, nonmetallic and metallic cables, cable tray, wireways and auxiliary gutters and so forth.

Section 300.3(B)(1) Paralleled Installations

Section 300.3(B)(1) has been revised to require that connections, taps or extensions from paralleled conductors are made in a manner to equalize the current on the parallel arrangement that is being tapped. This revision provides additional clarity for the termination of, and tapping from, paralleled conductors. 310.10(G), formerly 310.10(H), does not address potential inappropriate connections to individual conductors of an overall parallel arrangement.

Section 300.7(A) Sealing

Section 300.7(A) has been revised to correlate with Section 225.27. Products used to seal raceways or sleeves must be identified for the use. Compatibility with the cable/conductor insulation, bare conductor, shields or other component is now required.

Section 300.25 Exit Enclosures (Stair Towers)

New Section 300.25 has been added to Article 300 and addresses the installation of wiring methods in stair towers. Only wiring methods serving equipment in the stair enclosure and permitted by the AHJ are to be installed in the stair enclosure. This new section aligns with existing requirements in NFPA 101, which is the Life Safety Code.

Sections 310.1 Scope, 310.3(A) Minimum Size Conductors, and 310.3(B) Conductor Material

The scope of Article 310 has been revised and is now limited to not more than 2,000 volts (V). Requirements and ampacity tables for conductors over 2,000V have been relocated into a new Article 311, “Medium Voltage Conductors and Cable.” Copper-clad aluminum conductors must meet the material requirements of 310.3(B).

Section 312.8(B) Power Monitoring or Energy Management Equipment

Section 312.12(B) has been arranged into a list format for usability. Section 312.8(B) has been revised to address the equipment installed for both power monitoring and energy management systems. Additional requirements have been added for conductors used exclusively for control or instrumentation circuits.

Section 314.16 Number of Conductors in Outlet, Device, and Junction Boxes and Conduit Bodies

The single volume allowance for equipment grounding conductors (EGC) and equipment bonding jumpers (EBJ) is now limited to just four of these conductors. Having to take a full-size deduction is not practical in many cases. A one-quarter volume allowance based upon the largest EGC or EBJ in the box is added for each EGC or EBJ over four. Editorial revisions have been made in the parent text and in Table 314.16(A).

Section 330.130 Hazardous (Classified) Locations

New Section 330.130 provides construction requirements for type MC-HL cable. Type MC-HL cable is constructed to the UL Product Category (PJPP), Cable for Use in Hazardous Locations. Type MC-HL cable is recognized for limited use in some hazardous-location applications.

Section 334.30 Securing and Supporting

New text in 334.30 mandates that the cable length between the cable entry and the closest cable support shall not exceed 18 inches. This is necessary where loops are left for future modifications. All references to and requirements for Type NMS cable have been deleted throughout Article 334.

Section 336.10 Uses Permitted

Article 336 provides rules for power and control tray cable and Type TC. Only Type TC-ER-JP cable containing both power and control conductors is permitted in one- and two-family dwelling units. Type TC-ER-JP cable installed on the exterior of a dwelling unit must comply with Part II of article 340. Type TC cable is now permitted in hazardous (classified) locations where specifically referenced elsewhere in the NEC.

Sections 342.10(E), 344.10(E) and 358.10(E) Physical Damage and Severe Physical Damage

Physical damage is now specifically addressed in the .10(E) sections for intermediate metal conduit (IMC), rigid metal conduit (RMC) and electrical metallic tubing (EMT). IMC and RMC are permitted to be installed in areas subject to severe physical damage. EMT is permitted to be installed in areas subject to physical damage, but not in areas subject to severe physical damage.

Section 392.30(B) Cables and Conductors and Section 392.44 Expansion Splice Plates

Cable ties used in cable trays must be listed and identified for the application and securement and support. Cable ties for securement and support must be marked with the suffix S, 2S or 21S. Expansion splice plates for cable trays are required where necessary to compensate for thermal expansion and contraction.

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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