The basic purpose of a generator is to provide electric power whenever the supply from the local electric utility company suffers an interruption. Depending on the application, a generator can be a luxury item or a critical system that is required by law:

  • In households, the main function of a generator is to provide comfort for occupants: Normally there are no drastic consequences from interrupting the power supply, but it can cause discomfort, especially during nighttime when lighting is needed, or during hot or cold days when HVAC systems are used extensively.
  • In commercial locations, there is actually a financial benefit from owning a generator because it allows business operations to continue even when there is no power supply
  • Finally, there are locations when backup power is critical. For example, if any healthcare facility is left without backup power even for a short amount of time, the consequences can be severe

Backup power systems can be classified into two subtypes, depending on how critical their role is:

  • Emergency power systems are those that provide backup power for building systems that create a safety hazard for humans if they cease to operate. Due to their critical role, emergency power systems are always required by law
  • Standby power systems may be either optional or required by law, depending on local codes. They provide backup power for building systems that may cause discomfort or business disruption if they cease to operate, but where there is no hazard to human life in case of an interruption

In the case of New York City, the requirements for emergency and standby generators are established in Chapter 27 of the 2014 New York City Building Code. In addition, these systems must comply with the two following standards from the National Fire Protection Association (NFPA):

  • NFPA 110 – Standard for Emergency and Standby Power Systems
  • NFPA 111 – Standard on Stored Electrical Energy Emergency and Standby Power Systems

General Requirements

Some requirements in the New York City Building Code apply regardless of whether the generator is used to supply emergency or backup power.

  • The fuel supply on site must be sufficient for the generator to operate at full output for at least six hours.
  • Diesel is the preferred source of fuel for a generator and is code required for all Legally Required Emergency Systems. Diesel fuel is stored on site in either a fuel tank mounted to the base of the generator (sub-base fuel tank) or in a remote tank with a day tank in the generator room.
  • Natural gas from the utility company is allowed as the fuel source in Residential Group R-2 occupancies and for standby power systems, but it requires a cut-off valve to separate the supply from that of other appliances that run on gas.
  • All generators must be listed according to the UL 2200 standard by Underwriters Laboratories
  • Generators and their associated electrical distribution systems must be located in a separate room from the main electrical service equipment. This must be a dedicated room with a fire barrier rated for at least two hours and/or horizontal assemblies according to section 712 of the NYC Building Code
  • Only fuel tanks that will be used for the generator are allowed in the room, and the only piping allowed is that of sprinkler systems, or any piping required by generator cooling systems. Piping associated with other systems may go through the room, but only if it is uninterrupted
  • Multiple generators may share a fuel supply if they will power only emergency loads, or a combination of emergency and optional standby loads
  • All equipment that is powered by fuel combustion, including emergency and standby generators, must be registered with the NYC Department of Environmental Protection
  • Automatic transfer switches and their associated electrical feeders must be located in a separate room from both the main service equipment and the generator. If the ATS is not located at the load, it must have a dedicated room with similar requirements as that used for the generator: a 2-hour fire barrier or horizontal assemblies, and having no piping other than sprinkler systems

When is a Generator Required for Emergency Power?

As mentioned above, emergency generators are legally required for any electrical systems where interruption of the power supply can cause hazards for human life. The NYC Building Code requires emergency power in the following applications:

  • Voice and alarm systems in occupancies classified as Assembly Group A: this includes most locations where groups of people gather for civic, social, religious or similar purposes.
  • All exit signs and means of egress illumination must be provided with emergency power, regardless of location, even those on temporary buildings such as tents. Note that this can be accomplished using battery backup systems for smaller buildings and in certain occupancies.
  • Semiconductor fabrication facilities
  • Any location with toxic, highly toxic or pyrophoric materials must have emergency power, and in the case of hazardous materials it can be either standby or emergency power
  • High-rise and underground buildings must have both emergency and standby power.
  • Doors in occupancies classified as Institutional Group I-3, inhabited by five or more persons who are under restraint due to security reasons, for example prisons and mental healthcare facilities
  • Emergency power is required for specific elevator system components: controls, cab lights, ventilation and any equipment that is necessary for operation

Special Requirements for Occupancy Groups R-1, B and E

All occupancies that are classified as Residential Group R-1 must be equipped with both emergency and standby power, as well Business Group B and Educational Group E that meet the following conditions:

  • Having an occupied floor more than 75 feet above the lowest access for fire trucks
  • An area exceeding 15,000 square feet per floor, or 100,000 square feet in total

The emergency power system in these occupancy groups must be capable of powering exit signs, means of egress illumination, elevator car lighting, voice/alarm communication systems, automatic fire detection systems, fire alarm systems and electrical fire pumps.

When is a Generator required for Standby Power?

Although standby power is optional in many scenarios, the NYC Building Code makes it mandatory in the following cases:

  • Smoke control systems
  • Elevators that are part of an accessible means of egress
  • All components of normal elevator systems for which emergency power is not required
  • Horizontal sliding doors
  • Auxiliary inflation systems in membrane structures
  • Locations where hazardous materials are stored must have either standby or emergency power
  • Any location with organic peroxides
  • Voice and alarm communication systems in covered malls
  • High-rise and underground buildings
  • Airport traffic control towers
  • >
  • Smoke-proof enclosures
  • Pressurized elevator shafts

Special Requirements for Occupancy Groups R-1, B and E

The general requirements for standby power in these locations are the same presented in the section for emergency power. The specific building systems that require standby power are: ventilation systems that are used for smoke control, staircase pressurization systems and the fire command center. At least three elevators at a time must be supplied with standby power, with a manual switch to transfer the power supply to other elevators if needed

Generators Providing Optional Standby Power

As implied by their name, optional standby power systems are those not required by law. However, whenever they are deployed, they must be capable of powering the following systems in addition to their normal load:

  • Emergency lighting
  • Fire alarm systems
  • Elevators, according to the following requirements:
    • In Residential Group R-2 occupancies taller than 125 feet, the optional standby generator must be able to power one elevator that serves all floors. If multiple banks of elevators serve separate floors, one elevator per bank must be powered
    • In any other buildings with occupied floors more than 75 feet above the lowest fire truck access, the optional standby generator must be able to power at least one elevator that serves all floors

Normally, these systems would be powered by emergency or legally-required standby generators, but the optional standby power system must be able to take over the load as an additional safety measure

Concluding Remarks

Code compliance is a very important factor in any project where an electric generator will be installed. In addition to being necessary for the project to be approved during inspections, code compliance ensures safe conditions for all building occupants

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