Under what condition is liquidtight flexible metal conduit allowed to be used as an equipment grounding conductor?

Liquidtight flexible metal conduit (LFMC) is designed to interface with wiring systems in environments that require flexibility, particularly where movement or vibrations are expected. The National Electrical Code (NEC) permits the use of LFMC as an equipment grounding conductor under specific circumstances, and one of those crucial conditions is when flexibility is necessary after installation to accommodate movement or vibration.

In scenarios where machinery or equipment may be in motion, using rigid conductors may lead to strain and potential damage to the grounding system. The flexible nature of LFMC allows it to adapt to these conditions while still providing a safe and effective grounding path. This quality makes option A the most applicable, as it directly links the use of LFMC as an equipment grounding conductor to its inherent flexibility and the need for movement in certain applications.

The other options do not align with the NEC provisions for using LFMC as a grounding conductor. For instance, humidity levels and the number of circuits contained are not the determining factors for employing LFMC in this role. Additionally, while a rigid structure might denote strength, it contradicts the very definition of flexible conduit, which is specifically intended to provide flexibility rather than rigidity.