Legally required standby generators play a critical role in ensuring safety and continuity in facilities where power loss could result in hazards or regulatory non-compliance. According to the National Electrical Code (NEC) Article 701, these systems are defined as power sources that are legally mandated by a government authority having jurisdiction (AHJ) and must automatically supply electricity to specific non-emergency loads when normal power fails.
The authority having jurisdiction determines what constitutes a legally required standby system based on local building codes. A key technical requirement: these systems must start and supply power within 60 seconds of utility failure.
Testing & Maintenance Requirements
Once installation is complete, testing must be conducted—or witnessed—by the AHJ. Ongoing periodic testing and battery maintenance are also mandatory. You must include provisions for load testing, and a written (or electronic) record of all tests and maintenance activities must be maintained. While the NEC doesn’t specify a retention period for these records, it’s best practice to retain them in line with industry standards and manufacturer recommendations.
For broader guidance, NEC Article 110 outlines general testing obligations that apply across all standby power systems.
Capacity & Load Management
Legally required standby generators must be capable of handling all loads expected to operate simultaneously. While these systems may support both legally required and regular building loads, the generator must shed non-critical loads if it cannot support everything concurrently.
Transfer Switches & Equipment
NEC mandates that all transfer switches used in legally required systems be:
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Automatic
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Electrically operated
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Mechanically held
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Listed for emergency use
While legally required and optional standby loads can share a transfer switch, emergency loads must use a dedicated switch.
If budget allows, including a bypass/isolation feature for your transfer switch is a best practice. This ensures continuous power delivery to critical loads during maintenance or equipment failure.
Signage & Labeling
To comply with NEC standards, place clearly visible signage at the service entrance identifying all on-site emergency power sources and their locations.
Wiring Provisions
Wiring for legally required standby systems may share spaces with general wiring. However, proper labeling and installation methods must still be followed to avoid confusion or code violations.
Alarm & Monitoring Systems
As a baseline, NEC Article 701.6 requires the installation of an audio/visual annunciation system that:
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Indicates when the generator is supplying power
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Alerts operators to system faults (“derangement”)
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Notifies when the battery charger is not functioning
Most generator manufacturers offer integrated alarm and monitoring solutions that exceed NEC minimums, providing better diagnostics and operational reliability. Additionally, ground fault protection indication is also required.
Fuel Storage & Reliability
If you’re using a diesel-powered generator, you must maintain at least two hours’ worth of on-site fuel. For systems driven by a prime mover, dual supplies of both fuel and cooling water must be available. Public utility gas and municipal water supplies alone do not meet NEC reliability standards.
There is an exception: your AHJ may waive these requirements if they determine that the risk of simultaneous utility and fuel supply failure is negligible—but such waivers are rare.
Automatic starting is mandatory, along with a minimum 15-minute re-transfer delay to prevent short-cycle switching during brief utility power returns.
Overcurrent Protection & Selective Coordination
Per NEC Article 701.27, overcurrent protection devices must not be accessible to unauthorized individuals. It’s essential to perform a selective coordination study—led by a qualified professional—during system design. This ensures protective devices are appropriately coordinated with upstream overcurrent protection to minimize outages and comply with NEC requirements.
Final Considerations
Before installation, confirm your contractor understands the differences between legally required and optional standby systems. The generator set (genset) may be identical, but the installation requirements differ significantly under NEC codes.
Also note: outdoor generator units do not require an additional disconnect if the main disconnect is easily accessible and located within 50 feet of the building.
For more insight into standby systems, code compliance, and emergency power solutions, follow Knower Network for expert updates and technical guidance.
