Flexible Metal Conduit (FMC)

Flexible Metal Conduit — the trade name is Greenfield — is a spiral-wound metal tube you can bend by hand. It's the standard way to make the final flexible connection to a light fixture, transformer or motor, and to snake wiring through spaces where a rigid raceway can't turn.

FMC has limits: it can serve as an equipment-grounding path only in short lengths with listed fittings and limited overcurrent, so a separate ground wire is often required. It also isn't for wet locations — that's what liquidtight is for — and lengths and support are restricted to keep it from sagging and straining.

When it applies

Flexible metal conduit, Greenfield, is the spiral-wound metal raceway you bend by hand for the last connection where rigid pipe cannot flex, motor whips, transformers, recessed fixtures. It absorbs a little vibration and lets you make an offset without a bender.

Common mistakes

• Relying on the FMC itself as the equipment grounding path beyond the short lengths and conditions the code allows, past that you need a separate EGC pulled inside.
• Overtightening or ignoring the minimum bend radius so the interlock kinks and pinches the conductors.
• Using plain FMC in wet or damp locations where liquidtight belongs instead.

In the field

On motor connections I pull a green wire inside the flex almost every time. The listing lets you skip it in short runs, but on a vibrating machine the interlocked ground works loose, and I would rather trust a bonded conductor than a spring of metal.