Where is FMC not permitted?

Q. What uses does the NEC permit and forbid for flexible metal conduit?

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A. According to 348.10 of the NEC, flexible metal conduit (FMC) is permitted in exposed or concealed locations. On the other hand, the locations where FMC is not permitted are much more specific. As noted in 348.12, FMC shall not be used:

•     In wet locations.
•     In hoistways, other than as permitted in 620.21(A)(1).
•     In storage battery rooms.
•     In any hazardous location, except as permitted by 501.10(B).
•     Exposed to material having a deteriorating effect on the installed conductors.
•     Underground or embedded in poured concrete.
•     If subject to physical damage.

Exception No. 1: Where FMC is fished between access points through concealed spaces in finished buildings or structures and supporting is impracticable.

Exception No. 2: Where flexibility is necessary after installation, lengths from the last point where the raceway is securely fastened shall not exceed the following:

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1. 900 mm (3 ft) for metric designators 16 through 35 (trade sizes 1/2 through 11/4)
2. mm (4 ft) for metric designators 41 through 53 (trade sizes 11/2 through 2)
3. mm (5 ft) for metric designators 63 (trade size 21/2) and larger

Exception No. 3: Lengths not exceeding 1.8 m (6 ft) from a luminaire terminal connection for tap connections to luminaires as permitted in 410.117(C)

Exception No. 4: Lengths not exceeding 1.8 m (6 ft) from the last point where the raceway is securely fastened for connections within an accessible ceiling to a luminaire (s) or other equipment . For the purposes of this exception, listed flexible metal conduit fittings shall be permitted as a means of securement and support.

FMC shall be securely fastened in place by an approved means within 300 mm (12 in.) of each box, cabinet conduit body , or other conduit termination and shall be supported and secured at intervals not to exceed 1.4 m (4ft). Where used, cable ties shall be listed and be identified for securement and support.

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