Electrician's Licensing Practice Exam

What is the proper way to ground a subpanel within the same building?

1. Run a two-wire system

2. Run a four-wire system

3. Use a single ground wire only

4. Connect directly to the ground rod

The correct answer is: Run a four-wire system

A subpanel within the same building must be grounded using a four-wire system, which includes two hot wires, one neutral wire, and one ground wire. This configuration is essential to ensure safety and compliance with electrical codes. The neutral and ground must be kept separate in subpanels to prevent ground faults and ensure that the grounding system functions correctly. By running a four-wire system, the ground wire provides a safe path for fault currents, while the neutral wire carries the return current. This setup minimizes the risk of electric shock and equipment damage, as it prevents neutral currents from flowing through the ground connection, ensuring that the ground wire serves solely for fault protection. In contrast, other options such as a two-wire system do not provide a separate ground, thus compromising safety. Using only a single ground wire or connecting directly to a ground rod is also inadequate as these methods do not provide a reliable return current path and fail to meet the necessary electrical standards required for subpanels. Therefore, a four-wire system is the recognized standard for grounding subpanels to ensure both safety and compliance with electrical codes.