Under what condition is AC cable (BX) permitted to be unsupported?

The correct answer is based on specific regulations regarding the installation of AC cable (often referred to as BX or armored cable). According to the National Electrical Code (NEC), AC cables can be unsupported provided they do not exceed a certain length, which is typically 2 feet or less. This rule is in place to ensure that the cable is adequately supported and protected from damage that could result from sagging or tension that may occur over longer spans.

When AC cables are longer than 2 feet, they must be properly secured and supported at specified intervals to maintain safety and functionality. Supporting cables correctly helps prevent stress on the connections and reduces the risk of mechanical damage or electrical failure.

Given this context, lengths of 2 feet or less allow for the flexibility of installation without the need for additional support, adhering to safety standards while facilitating easier installation.