Under what condition must a generator be grounded as a separately derived system?

A generator must be grounded as a separately derived system when it switches the grounded conductor. This is because grounding is essential for ensuring safety and preventing electrical shock hazards in systems where the grounded (neutral) conductor is switched or disconnected. When the grounded conductor is switched, there is a potential that the neutral may not be connected to ground at all times, which can create an unsafe condition.

Grounding the generator establishes a reference point for the electrical system, helps in the coordination of protective devices, and mitigates the risk of electrical faults. Additionally, grounding helps to manage fault currents safely, directing them to ground rather than allowing them to energize equipment or pose a risk to personnel.

In scenarios where the generator is directly connected to a building’s main service, already has solid grounding through the main system, or is located outdoors, additional grounding of the separately derived system may not be required in the same way. Therefore, the condition that specifically necessitates grounding as a separately derived system involves the switching of the grounded conductor.