| A. General •350-1. Scope. This article covers the use and installation of flexible metal conduit and associated fittings.
•350-2. Definition. Flexible metal conduit is a raceway of circular cross section made of helically wound, formed, interlocked metal strip.
•350-3. Other Articles. Installations of flexible metal conduit shall comply with the applicable provisions of Article 300.
•350-4. Uses Permitted. Flexible metal conduit shall be listed and shall be permitted to be used in exposed and concealed locations.
•350-5. Uses Not Permitted. Flexible metal conduit shall not be used:
- In wet locations unless the conductors are approved for the specific conditions and the installation is such that liquid is not likely to enter raceways or enclosures to which the conduit is connected.
- In hoistways, other than as permitted in Section 620-21(a)(1).
- In storage-battery rooms.
- In any hazardous (classified) location other than as permitted in Sections 501-4(b) and 504-20.
- Where exposed to materials having a deteriorating effect on the installed conductors, such as oil or gasoline.
- Underground or embedded in poured concrete or aggregate.
- Where subject to physical damage.
B. Installation
•350-10. Size.
(a) Minimum. Flexible metal conduit less than 1/2-in. electrical trade size shall not be used unless permitted in (1) through (5) below for 3/8-in. electrical trade size:
- For enclosing the leads of motors as permitted in Section 430-145(b).
- In lengths not in excess of 6 ft (1.83 m) as part of a listed assembly, or for tap connections to lighting fixtures as permitted in Section 410-67(c), or for utilization equipment.
- For manufactured wiring systems as permitted in Section 604-6(a).
- In hoist-ways, as permitted in Section 620-21(a)(1).
- As part of a listed assembly to connect wired fixture sections as permitted in Section 410-77(c).
(b) Maximum. Flexible metal conduit larger than 4-in. electrical trade size shall not be used.
•350-12. Number of Conductors. The number of conductors permitted in a flexible metal conduit shall not exceed the percentage of fill specified in Table 1, Chapter 9, or as permitted in Table 350-12 for 3/8-in. flexible metal conduit.
•350-14. Grounding. Flexible metal conduit shall be permitted as a grounding means as covered in Section 250-91(b). Where an equipment bonding jumper is required around flexible metal conduit, it shall be installed in accordance with Section 250-79.
Exception: Listed flexible metal conduit shall be permitted as a grounding means if the total length in any ground return path is 6 ft (1.83 m) or less, the conduit is terminated in fittings listed for grounding, and the circuit conductors contained therein are protected by overcurrent devices rated at 20 amperes or less. Where used to connect equipment where flexibility is required, an equipment grounding conductor shall be installed.
•350-16. Bends. There shall not be more than the equivalent of four quarter bends (360 degrees total) between pull points, e.g., conduit bodies and boxes. Bends in the conduit shall be made so that the conduit will not be damaged and the internal diameter of the conduit will not be effectively reduced. The radius of the curve of the inner edge of any field bend shall not be less than shown in Table 346-10.
•350-18. Supports. Flexible metal conduit shall be securely fastened in place by an approved means within 12 in. (305 mm) of each box, cabinet, conduit body, or other conduit termination and shall be supported and secured at intervals not to exceed 4 1/2 ft (1.37 m).
Exception No. 1: Where flexible metal conduit is fished.
Exception No. 2: Lengths not exceeding 3 ft (914 mm) at terminals where flexibility is required.
Exception No. 3: Lengths not exceeding 6 ft (1.83 m) from a fixture terminal connection for tap connections to light fixtures as permitted in Section 410-67(c). Horizontal runs of flexible metal conduit supported by openings through framing members at intervals not greater than 4 1/2 ft (1.37 m) and securely fastened within 12 in. (305 mm) of termination points shall be permitted.
•350-20. Fittings. Fittings used with flexible metal conduit shall be listed. Angle connectors shall not be used for concealed raceway installations.
•350-22. Trimming. All cut ends of flexible metal conduit shall be trimmed or otherwise finished to remove rough edges, except where fittings that thread into the convolutions are used.
•350-24. Splices and Taps. Splices and taps shall be made in accordance with Section 300-15. See Article 370 for rules on the installation and use of boxes and conduit bodies.
Table 350-12. Maximum Number of Insulated Conductors in 3/8-inch Flexible Metal Conduit*
Col. A = With fitting inside conduit
Col. B = With fitting outside conduit
Size
AWG |
Types RFH-2, SF-2 |
Types TF, XHHW, AF, TW |
Types TFN, THHN, THWN |
Types FEP, FEPB, PF, PFG |
|
A |
B |
A |
B |
A |
B |
A |
B |
| 18 |
2 |
3 |
3 |
5 |
5 |
8 |
5 |
8 |
| 16 |
1 |
2 |
3 |
4 |
4 |
6 |
4 |
6 |
| 14 |
1 |
2 |
2 |
3 |
3 |
4 |
3 |
4 |
| 12 |
... |
... |
1 |
2 |
2 |
3 |
2 |
3 |
| 10 |
... |
... |
1 |
1 |
1 |
1 |
1 |
2 |
*In addition, one covered or bare equipment grounding conductor of the same size shall be permitted |
