An equipotential zone is suitable for use with which types of vehicles?

An equipotential zone is a safety measure utilized in environments where electrical hazards may be present, often seen in substation operations. The purpose of creating such a zone is to equalize the electric potential, thereby minimizing the risk of electric shock to personnel and vehicles.

Given this context, vehicles that operate in or around these areas need to be specifically designed or used considering these safety features. Trucks and digger derricks are both types of vehicles that can operate near electrical hazards; however, the design and operation of vehicles are crucial in maintain safety in equipotential zones.

The correct understanding is that such zones are not suitable for standard operation of either trucks or digger derricks without specific adaptations, training, or procedures that ensure safety. Therefore, if the options provided indicate no vehicle type is suitable for operation in conventional senses, then asserting that none are appropriate aligns with the safety and operational standards expected in these contexts. Hence, the option that indicates none of the above is suitable is justified given the safety regulations.