How long of a conduit nipple is allowed to be filled to 60% capacity?

The correct answer relates to the maximum allowable length of a conduit nipple that can be filled to 60% capacity, which is a regulation often referenced in electrical installation standards. In this context, a conduit nipple is a short length of conduit used to connect two other pieces of conduit or to connect conduit to a box or fitting.

The standard guideline for filling conduits is designed to ensure that there is adequate space for the wires within the conduit to avoid overheating and allow for safe operation of electrical systems. The 60% fill rule is commonly applied to maintain proper airflow and cooling in electrical installations.

According to the National Electrical Code (NEC), the maximum length of a conduit nipple (or any conduit for that matter) that can be filled to 60% of its capacity should not exceed 24 inches. This length restriction helps ensure that there is sufficient space for the conductors to be installed safely without overcrowding.

In this case, while other lengths are mentioned, the allowable maximum length of 24 inches aligns with the code requirements, making it the appropriate choice for this question.