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Stumped by the Code? NEC Requirements for Installing, Securing, and Supporting FMC

Oct. 11, 2023
Answering your NEC questions

Courtesy of www.MikeHolt.com

All questions and answers are based on the 2023 NEC.

Q:  What are the conditions flexible metal conduit (FMC) can be used and installed?

A: According to Sec. 348.10 of the NEC, FMC is permitted to be installed exposed or concealed.

Q: What is the minimum and maximum FMC trade size permitted?

A: The minimum and maximum FMC trade sizes permitted are found in Sec. 348.20.

(A) Minimum. Trade size ½, except trade size 3⁄8 is permitted for the following applications:

(1) For enclosing the leads of motors.

(2) Not exceeding 6 ft in length: 

a.  For utilization equipment,

b. As part of a listed assembly, or

c. For luminaire tap connections in accordance with Sec. 410.117(C).

(B) Maximum. Trade size 4.

Q: What are the requirements for securing and supporting FMC?

A: Section 348.30 gives the requirements for securing and supporting FMC.

(A) Securely Fastened. FMC must be securely fastened by a means approved by the authority having jurisdiction within 1 ft of termination, and it must be secured and supported at intervals not exceeding 4½ ft (see Figure below).

Where cable ties are to be used to secure and support Type FMC, they must be listed and identified for securing and supporting.

Exception No. 1: Type FMC is not required to be securely fastened or supported where fished between access points through concealed spaces and supporting is impractical.

Exception No. 2: If flexibility is necessary after installation, unsecured lengths from the last point the raceway is securely fastened are not permitted to exceed:

(1) 3 ft for trade sizes ½ through 1¼

(2) 4 ft for trade sizes 1½ through 2

(3) 5 ft for trade sizes 2½ and larger

Exception No. 4: Lengths not exceeding 6 ft from the last point where the raceway is securely fastened can be unsecured within an accessible ceiling for a luminaire(s) or other equipment. Listed fittings are considered a means of securement and support. 

(B) Horizontal Runs. FMC installed horizontally in bored or punched holes in wood or metal framing members, or notches in wooden members, at intervals not more than 4½ ft is considered supported, but the raceway must be secured within 1 ft of terminations.

These materials are provided by Mike Holt Enterprises in Leesburg, Fla. To view Code training materials offered by this company, visit www.mikeholt.com/code.

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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