All parts of metal cable tray must be bonded together and?

• A. Bonded
• B. Isolated
• C. Insulated
• D. Grounded

Answer: (D)

The important idea is that metallic cable trays must be kept at the same electrical potential and tied to the earth so a fault has a safe path to clear quickly. Bonding all metal parts together prevents voltage differences between sections or between the tray and other metalwork. Grounding then provides the actual low-impedance connection to earth through the equipment grounding conductor, so if insulation fails and the tray becomes energized, fault current flows to ground and overcurrent protection can trip.

If the tray were isolated or insulated, there would be no reliable fault path, which could leave the tray energized and pose a shock hazard. Bonding without grounding wouldn’t establish a true earth reference, so a fault could still cause dangerous conditions. Grounding completes the safety setup by giving a clear path to earth.