Which transformer secondary is required to be grounded?

The requirement for grounding transformer secondaries is critical for ensuring safety and functionality in electrical systems. When it is stated that all transformer secondaries should be grounded, it refers to the need for proper grounding to protect against electrical faults and to stabilize the system.

Grounding the 120 to 12 volt AC transformer installed outside is essential because it minimizes the risk of electric shock and mitigates the effects of lightning strikes or surges, especially considering that outdoor installations are more susceptible to environmental factors.

For the 480 to 120/240 VAC, 1Ø, 3-wire system supplying a panelboard, grounding is equally important. It provides a path for fault currents, helping to prevent dangerous voltage levels from appearing on exposed conductive parts, which could be hazardous to users.

In the case of the 480 to 120 VAC for a motor control circuit, grounding serves to protect control circuits and motors from insulation failures and random fault currents, ensuring reliable operation and user safety.

In summary, grounding transformer secondaries is a fundamental practice across various applications to enhance safety, improve equipment performance, and comply with electrical codes and standards.