This is a nuanced question with no single, definitive "yes" or "no" answer. The requirement for ground fault protection on the generator's main breaker depends on several factors and requires careful consideration of the NEC (National Electrical Code) and good engineering practices. Here's a breakdown of the key considerations

NEC Requirements (Generally):
NEC 230.95 (Ground-Fault Protection of Equipment)

This section applies to solidly grounded wye electrical services of more than 150 volts to ground but not exceeding 1000 volts phase-to-phase for each service disconnecting means rated 1000 amperes or more. This is what triggers the original ground fault protection at the service switch.



Article 700 (Emergency Systems), 701 (Legally Required Standby Systems), 702 (Optional Standby Systems)

These articles address emergency, legally required standby, and optional standby generators. They may impose additional requirements related to ground fault protection, transfer switches, and coordination, depending on the application of the generator. These articles modify or supplement the general rules in Chapters 1-4 of the NEC.

Coordination/Selective Coordination

The NEC strongly emphasizes selective coordination (selective tripping) of overcurrent protective devices. This means that the device closest to the fault should trip first, minimizing the impact of the fault. This is especially important in emergency and standby systems.

Key Considerations for the Generator Breaker


Is the Generator Part of an Emergency/Standby System (700, 701, 702)? If so, this changes the game. Emergency Systems (700): Likely requires selective coordination. Legally Required Standby Systems (701): Also likely requires selective coordination. Optional Standby Systems (702): Less stringent, but coordination is still good practice.2.

Selective Coordination with the Service Ground Fault Protection

This is the most important consideration. You MUST analyze whether the generator breaker's ground fault protection (if present) will coordinate with the service's ground fault protection.

Scenario A: No Coordination (Generator trips first)

If the generator breaker's ground fault protection is more sensitive or faster than the service's ground fault protection, the generator will trip first in the event of a ground fault anywhere in the system downstream of the service. This is generally undesirable. The service ground fault protection is designed to protect the service equipment and main distribution, and should operate first for downstream faults. Having the generator trip first could disrupt power to essential loads longer than necessary. In this scenario, NOT having ground fault protection on the generator breaker might be better, as it forces the service ground fault protection to clear the fault, ensuring the generator remains available.

Scenario B: Good Coordination (Service trips first)

If the generator breaker's ground fault protection is less sensitive or slower than the service's ground fault protection, the service will trip first for downstream faults, and the generator will only trip for faults specifically within the generator or its directly connected equipment. This is ideal. The generator continues to supply power to its designated loads if the fault is elsewhere in the system.3.

Generator Size and Application

If the generator is small and only supplies a few critical loads, the risk of a ground fault within the generator system may be low enough that ground fault protection is deemed unnecessary IF coordination with the service is assured. If the generator is large and supplies a significant portion of the facility's load, ground fault protection might be considered a best practice, as long as it coordinates properly.4.

Generator Neutral Grounding

The method of grounding the generator neutral also affects the need for and type of ground fault protection.5.

AHJ (Authority Having Jurisdiction)

The local electrical inspector (AHJ) has the final say. They may have specific requirements or interpretations of the NEC. Always consult with the AHJ during the design phase.

In summary, to answer your question directly



Not necessarily. It depends.

Recommendation


Perform a Short Circuit and Coordination Study

This is the ONLY way to determine if ground fault protection is needed on the generator breaker and to ensure proper coordination with the service. This study will model the system's fault currents and protective device characteristics.2.

Consult with a Qualified Electrical Engineer

An engineer experienced in power systems and the NEC can help you design a safe and code-compliant system.3.

Coordinate with the AHJ

Discuss your design with the local electrical inspector to ensure it meets their requirements.

General Guidance



Favor Selective Coordination

The primary goal is to ensure that only the protective device closest to the fault trips, minimizing disruption.

Err on the Side of Safety

If in doubt, consider adding ground fault protection to the generator breaker, but only if it can be coordinated.

Document Your Decision:* Clearly document the rationale behind your decision regarding ground fault protection, including the results of any studies or analyses.Without a short circuit and coordination study, it's impossible to give a definitive answer. Proper engineering is essential to ensure a safe and reliable power system. Flag for review