In a sub-station, stand on a ____________ that is bonded to the steel structure to ensure that the operator's feet and hands will be at the same potential if things go wrong.

• A. Rubber grid or platform
• B. Ground gradient grid or mat
• C. Wooden grid or platform
• D. Concrete grid or platform

Answer: (B)

The safety idea here is equipotential protection: keep the surface you stand on at the same electrical potential as the surrounding steel structure so that a fault doesn’t create a dangerous voltage difference across your body. A ground gradient grid or mat is conductive and bonded to the station’s grounding system, so the operator’s feet and hands stay at the same potential even if parts of the system energize. That minimizes the risk of shock from touch or step potentials.

Rubber, wood, or concrete are insulators or non-bonded surfaces, which can isolate you from the grounding system and allow voltage differences to develop between your feet and hands during a fault. That’s why they’re not suitable for this purpose.