What Are Emergency Standby Generators?
Emergency standby generators are legally required systems classified as “emergency” by the governing authority in a jurisdiction. According to NEC Article 700.2, these generators are designed to automatically supply power and illumination essential for human safety within 10 seconds of a power outage. The local Authority Having Jurisdiction (AHJ) can classify any generator as an emergency generator as needed.
Emergency systems are crucial for maintaining power to life-supporting equipment, fire detection and alarm systems, elevators, fire pumps, public safety communication systems, and other essential operations (NEC Article 700.1).
Testing and Maintenance Requirements
The AHJ mandates testing and inspection after installation. Additionally, periodic testing and maintenance of battery systems are required to ensure compliance.
Key maintenance requirements include:
- Testing all emergency lighting and power systems under full load conditions.
- Keeping written or electronic records of maintenance and test results.
- Following manufacturer recommendations for testing and maintenance, as the NEC does not specify detailed requirements.
For additional guidance, NEC Article 110 outlines general testing requirements for all standby power supply systems.
Generator Capacity Considerations
Emergency standby generators must have the capacity to handle all designated emergency loads. While these generators can supply power to an entire facility, non-emergency loads must be shed if capacity is insufficient to support all loads during an emergency.
Transfer Equipment for Emergency Generators
Transfer switches for emergency generators must be:
- Automatic
- Listed and approved for emergency use
- Mechanically held
- Authorized by the AHJ
When an emergency generator serves both emergency and non-emergency loads, multiple transfer switches must be used. One switch must be exclusively designated for emergency loads. Note that meter-mounted switches are not permitted for emergency use.
Signage and Labeling Requirements
A sign must be installed at the service entrance, indicating the type and location of all on-site emergency power sources.
Surge Protection
To protect emergency power systems from voltage surges, a listed surge protection device is required for all emergency system panel boards and switchboards.
Emergency Circuit Wiring Standards
To prevent accidental disconnections or failures, emergency circuit wiring must remain separate from normal system wiring (with limited exceptions). Emergency power system enclosures and boxes must be permanently labeled for identification.
Signal and Alert Systems
Emergency standby systems require audio and visual alerts to indicate:
- Emergency source failure
- Battery operation status
- Non-functioning battery charger
- Ground fault conditions
Fuel Storage and Supply
- Diesel Generators: Must have at least a two-hour fuel supply on-site at all times.
- Prime Mover-Driven Systems: Require dual fuel and water supply if water is used in the cooling system. Public utility natural gas and municipal water supply alone are not considered reliable for emergency power systems.
- The AHJ may grant exceptions if there is minimal risk of simultaneous power and fuel supply failure.
For prime mover applications, automatic starting capabilities are required, along with a minimum 15-minute retransfer delay to prevent short-term utility power fluctuations from causing unnecessary switchovers.
Additional Compliance Considerations
- The AHJ must approve all installed equipment, favoring listed equipment over unlisted alternatives.
- Outdoor generator sets do not require an additional disconnect switch if the main disconnect is within 50 feet and easily accessible.
- Emergency generators do not require ground fault protection but must have indicators to detect ground faults.
- A temporary emergency power source is required if the standby generator is out of service for an extended period.
Final Thoughts
This article provides an overview of NEC Article 700 regulations for emergency standby generators. For complete compliance requirements, refer to NEC 2020 Article 700. Ensuring your generator meets these standards is crucial for maintaining safety and reliability in critical situations.
