Electrical Requirements for Generators per NEC 2020
The National Electrical Code (NEC) 2020 outlines critical requirements for the installation, wiring, and operation of generators to ensure safety and reliability. Below are the key considerations for generator installations:
1. Generator Sizing (NEC 220)
Generators must be properly sized to accommodate the expected load, including both continuous and non-continuous operations, and any motor-driven equipment. Accurate load calculations are essential to ensure the generator can handle peak demand without overloading.
2. Transfer Switch Requirements (NEC 702.4, NEC 445.18)
A transfer switch is required to safely disconnect the generator from the utility supply to prevent backfeeding. The switch, whether manual or automatic, must be rated for the full load served by the generator and designed to isolate the utility during generator operation.
3. Grounding and Bonding (NEC 250)
Proper grounding and bonding are crucial for generator safety. Generators may be classified as separately derived systems, requiring a separate grounding electrode system, or non-separately derived systems, which rely on the existing service grounding. Grounding must be in accordance with NEC 250, providing a low-impedance path to direct fault currents safely to earth.
4. Overcurrent Protection (NEC 445.12)
Generators must be equipped with overcurrent protection devices to safeguard against short circuits and overloads. These devices, including circuit breakers or fuses, must be properly sized based on the generator’s output and connected loads to ensure fault conditions are isolated and contained.
5. Wiring and Conduit (NEC 300, NEC 445.13)
Wiring methods must comply with NEC 300, ensuring conductors are properly sized and insulated for the specific load and environment. Conduits or raceways must be used to protect wiring from physical damage, and conductor sizing must be based on both load and environmental conditions.
6. Generator Disconnect Means (NEC 445.18)
The NEC requires a disconnecting means for generators to provide a safe way to isolate the generator during maintenance or in an emergency. The disconnect must be readily accessible and clearly marked for ease of identification.
7. Location and Ventilation (NEC 445.11, NEC 110.26)
Generators must be installed in locations that provide adequate ventilation to prevent overheating and maintain performance. Clearance requirements around the generator must be adhered to, ensuring sufficient space for air circulation and maintenance. Outdoor generators must be housed in weather-resistant enclosures.
8. Labeling and Signage (NEC 702.7)
Proper signage is required at key points in the installation, including transfer switches, service panels, and the generator itself. These labels must indicate the presence of alternate power sources and provide clear instructions for operating personnel.
9. Size of Generator’s fire pump breaker(NEC 695)
- Generator’s fire pump breaker is between 125% to 250% of the rated amps
- This provides no overloaded protection(>125%)
- NEC 430 limits the maximum size to 250%
Questions should be Considered for Generator System Design:
- What is the total power demand, including continuous and peak loads?
- What type of loads will the generator be serving (Fire pump, elevator, …)?
- Is the electrical system single-phase or three-phase?
- What are the voltage requirements?
- Is future load expansion anticipated?
- What fuel type will be used, Natural gas or diesel?
- What are the local code and NEC 2020 requirements?
- Are there life-safety loads that require specific considerations?
- What type of transfer switch will be integrated, and is it compatible with the generator system?
- What is the desired runtime, and how will fuel storage be managed?
- Will the installation require noise attenuation or weather-proof enclosures?
- Check the Site address for emissions requirements.
- The generator must comply with NFPA 20, ensuring transient voltage does not dip more than 15% during normal fire pump startup with a functioning soft starter
Link to size the generator per GENERAC:
https://pdp.powerdesignpro.com/home
Presentation by GENERAC:
NEC requirement Part 1
Emissions and Sizing Part1
Generator Docking Station:
NEC 700.3(F) requires a permanent way to connect a temporary power source when the main emergency power system is offline for maintenance or testing.
A generator docking station is a device that connects a portable generator to a building’s electrical system.
There are many possible methods to achieve the requirement of 700.3(F). See below for one example.
DOCKING STATION WIRING FOR TWO ATS
DOCKING STATION 600AMP 2 POLE STATION LAY OUT