Is it true that the grounding wire must be connected to every metal box?

The grounding wire must indeed be connected to every metal box. This is a crucial safety measure designed to protect individuals from electric shock and to ensure that any stray currents have a safe path to ground. Metal boxes can conduct electricity, so if they become energized due to a fault, anyone touching the box could receive a shock. By grounding these boxes, any electrical fault will cause the circuit breaker to trip or blow a fuse, thereby cutting off the electrical supply and minimizing the risk of injury or fire. Grounding also helps to stabilize voltage levels in the electrical system, improving overall safety and performance.

In contrast, not all installations with electrical boxes require grounding. For example, non-metallic boxes, typically used in certain applications, do not necessitate a ground connection because they're constructed from materials that do not conduct electricity. Therefore, understanding that every metal box needs a grounding wire reinforces the importance of proper electrical grounding practices in promoting safety.