Circuits for electric cranes operating over combustible fibers in Class III locations shall not be ___.

Circuits for electric cranes operating over combustible fibers in Class III locations shall not be ___.

• A. spliced
• B. run in raceways
• C. THHN conductors
• D. grounded

Answer: (D)

In Class III locations, the risk comes from easily ignitable fibers that can ignite from electrical activity such as arcs or sparks. Keeping crane circuits ungrounded reduces the energy that could be released at a fault near those fibers, lowering the chance of ignition. Grounding would create a direct path to earth for fault current, which could produce a spark or heat near the fibers, so the circuits are kept ungrounded and designed with insulation and protective raceways to contain any fault energy. This approach aligns with using protected conductors like THHN in raceways, while splices and conductor routing are handled in accordance with enclosure and protection requirements; the key point here is that grounding is what's avoided.

In Class III locations, the risk comes from easily ignitable fibers that can ignite from electrical activity such as arcs or sparks. Keeping crane circuits ungrounded reduces the energy that could be released at a fault near those fibers, lowering the chance of ignition. Grounding would create a direct path to earth for fault current, which could produce a spark or heat near the fibers, so the circuits are kept ungrounded and designed with insulation and protective raceways to contain any fault energy. This approach aligns with using protected conductors like THHN in raceways, while splices and conductor routing are handled in accordance with enclosure and protection requirements; the key point here is that grounding is what's avoided.