Ecmweb 17510 Nec Code Quandaries Dec 2017 Pr
Ecmweb 17510 Nec Code Quandaries Dec 2017 Pr
Ecmweb 17510 Nec Code Quandaries Dec 2017 Pr
Ecmweb 17510 Nec Code Quandaries Dec 2017 Pr
Ecmweb 17510 Nec Code Quandaries Dec 2017 Pr

Stumped by the Code? Rules for Supporting and Securing Metal-Clad (Type MC) Cable

Dec. 22, 2017
Your most pressing National Electrical Code (NEC) questions answered

All questions and answers are based on the 2017 NEC.

Underlined text indicates a Code change.

Q. What are the NEC requirements for supporting and securing metal-clad (Type MC) cable?

A. Type MC cable must be supported and secured by staples, cable ties listed and identified for securing and supporting; straps, hangers, or similar fittings; or other approved means designed and installed so as not to damage the cable [330.30(A)].

Secured is “fastened” such as with a strap or tie wrap; supported is “held” such as with a hanger or through a hole in a stud, joist, or rafter.

Type MC cable with four or fewer conductors sized no larger than 10 AWG, must be secured within 12 in. of every outlet box, junction box, cabinet, or fitting and at intervals not exceeding 6 ft [330.30(B)].

Listed Type MC cable with ungrounded conductors 250kcmil and larger can be secured at 10-ft intervals when installed vertically.

Type MC cable must be supported at intervals not exceeding 6 ft. Cables installed horizontally through wooden or metal framing members are considered secured and supported if such support doesn’t exceed 6-ft intervals [330.30(C)].

Type MC cable can be unsupported and unsecured where [330.30(D)]:

 (1) Fished through concealed spaces in a finished building and support is impractical.

 (2) Not more than 6 ft long from the last point of cable support to the point of connection to a luminaire or electrical equipment within an accessible ceiling. For the purposes of this section, Type MC cable fittings are permitted as a means of cable support (Figure). 

 (3) Not more than 3 ft from the last point where it’s securely fastened to provide flexibility for equipment that requires movement after installation, or to connect equipment where flexibility is necessary to minimize the transmission of vibration from the equipment.

Q. What are the NEC requirements for supporting and securing nonmetallic-sheathed (Type NM) cable?

A. Nonmetallic-sheathed cable must be supported and secured by staples, straps, cable ties listed and identified for securing and supporting; hangers, or similar fittings, at intervals not exceeding 4½ ft and within 12 in. of the cable entry into enclosures or fittings [334.30].

Two-wire (flat) Type NM cable isn’t permitted to be stapled on edge.

Type NM cable installed within a raceway isn’t required to be secured within the raceway.

Type NM cable installed horizontally in bored or punched holes in wood or metal framing members, or notches in wooden members is considered secured and supported if the distance doesn’t exceed 4½ ft. Type NM cable must also be secured within 1 ft of termination [334.30(A)].

Informational Note: See Sec. 314.17(C) for support where nonmetallic boxes are used.

Unsupported Type NM cable is permitted for the following situations [334.30(B)]:

 (1) Where Type NM cable is fished between concealed access points in finished buildings and support is impracticable.

 (2) Not more than 4½ ft of unsupported cable is permitted from the last point of support within an accessible ceiling for the connection of luminaires or equipment in one-, two-, or multi-family dwellings.

 Type NM cable isn’t permitted as a wiring method above accessible ceilings, except in dwellings [334.12(A)(2)].

Holt is the owner of Mike Holt Enterprises, Inc. in Leesburg, Fla. He can be reached at www.mikeholt.com.
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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