What Should Be Connected to an Emergency Generator in a Commercial Building?

Jahnavi Sajip
Author : Jahnavi Sajip
June 20, 2018
5 Minutes Read

    Commercial buildings are characterized by the continuous presence of a large number of occupants, which means safety should be among the top priorities for the companies that own them. When addressing the topic of backup generators, the NYC Building Code classifies loads into two main categories: emergency loads and standby loads.

    Emergency loads include the equipment and building systems that would create life-threatening conditions if they stop operating. For example, exit signs and staircase lighting are always considered emergency loads, since evacuating a building without them is very difficult

    Standby loads may cause inconvenience or discomfort if they stop operating, but do not create risks like those involved if an emergency load is left without power. Keep in mind, however, that backup power for some standby loads is mandatory, especially loads that simplify troubleshooting during an electric service interruption, or if they are useful for rescue operations during an emergency.

    General Emergency and Standby Power Requirements for Commercial Occupancies in NYC

    Commercial buildings in New York City normally fall under one of the following occupancy classifications:

    • Assembly Groups A-1 through A-5, which include restaurants.
    • Business Group B, which includes office buildings
    • Educational Group E, which includes schools.
    • Institutional Groups I-1 through I-4, which include hospitals.
    • Mercantile Group M, which includes retail.

    The NYC Building Code provides a general list of emergency and standby loads for which backup power is mandatory, but there are additional requirements for the following occupancy groups:

    • Assembly Group A, all subgroups
    • Business Group B and Educational Group E, when the building has occupied floor space less than 75 ft above the lowest fire vehicle access, and a gross floor area above 15,000 ft2 per floor or at least 100,000 ft2 in total.
    • Institutional Group I-3: Correctional centers and mental hospitals
    • Special requirements also apply for covered malls, high-rise buildings and underground locations.

    The following table provides a list of all loads that must be connected to emergency power and standby power in NYC commercial occupancies. Requirements that are specific for some occupancies or building types are provided in the next section.



    1) Exit signs
    2) Means of egress lighting
    3) Elevator controls, cab lights and ventilation

    1) Smoke control systems
    2) Horizontal sliding doors
    3) Membrane structures
    4) Elevators
    5) Smokeproof enclosures
    6) Pressurized elevator shafts

    Emergency and Standby Power: Special Cases

    The NYC Building Code establishes additional requirements for some occupancy groups or building types. They are summarized in the following table, and keep in mind that the general requirements still apply.


    Emergency Power

    Mandatory Standby Power

    Group A

    1) Voice and alarm communication systems.

    None beyond general requirements.

    Group B and E that meet fire vehicle access and floor space conditions

    1) Emergency voice and alarm communication systems. This includes Auxiliary Radio Communication systems (ARCs) used by the Fire Department, even if they were installed voluntarily.

    2) Automatic fire detection systems.

    3) Fire alarms.

    4) Electrical fire pumps (manual, automatic, sprinkler booster pumps).

    1) Stair pressurization systems.

    2) At least three elevators with manual transfer to other elevators as needed.

    3) Fire command center power and lighting.

    Group I-3

    1) Electrical doors and locks.

    None beyond general requirements.

    Covered mall above 50,000 ft2

    None beyond general requirements.

    1) Emergency voice and alarm communication system.

    High-rise (non residential)

    1) Emergency voice and alarm communication systems. This includes Auxiliary Radio Communication systems (ARCs) used by the Fire Department.

    2) Automatic fire detection systems.

    3) Fire alarms.

    4) Electrical fire pumps (manual, automatic, sprinkler booster pumps, etc.).

    1) Fire command center power and lighting.

    2) Stair pressurization systems.


    1) Emergency voice and alarm communication systems. This includes Auxiliary Radio Communication systems (ARCs) used by the Fire Department.

    2) Automatic fire detection systems.

    3) Fire alarms.

    1) Electrical fire pumps.

    2) Stair pressurization systems.

    Optional Standby Power: Additional Requirements

    All loads not included in the tables above are considered optional standby loads, which means the NYC Building Code does not require a backup power system for them, but it can be installed anyway if considered appropriate. It is important to note, however, that the following loads must be added to any optional standby loads when sizing the generator:

    • Fire alarm systems
    • Emergency lighting
    • At least one elevator serving all floors, in buildings with occupied floors more than 75 ft above the lowest fire truck access

    Although these loads are normally covered by emergency or mandatory standby power systems, the code requires them to be counted for any optional standby system as a failsafe measure. In addition, the code allows the fuel supply to be shared among emergency and optional standby generators. Complementary equipment that is needed for generator operation can also be shared among emergency and optional standby units.

    When Is Optional Standby Power Recommended?

    There are many loads in commercial buildings that are not legally required to have standby power. When determining what to connect to an optional standby power system, the best recommendation is working closely with the property owner and using common sense.

    Refrigeration Systems

    When refrigeration systems stop operating, it is only a matter of time before the products and supplies they contain start to degrade. This may not be a critical issue in an office building that only has a few small refrigerators, but can have severe consequences in a restaurant or hospital, where large amount of food or medical supplies require low-temperature storage.

    In these cases, even if a standby power system is not legally required, it is in the best interest of the company to install it. In both cases, omitting the standby power system can have human health consequences. In addition, even if spoiled food or medical supplies are discarded, it represents a financial loss for the company.

    Water Pumping Systems

    The water supply is a key building system, especially when kitchens and bathrooms are present. Therefore, optional standby power is recommended if the building relies on water booster pump; otherwise, an electric service interruption will cut the water supply for upper floors.

    Networking Infrastructure

    Information technologies are key for modern business operations, and they generally represent a small energy expense compared with equipment such as water heaters and HVAC units. Lack of connectivity can disrupt business operations severely, and in hospitals it can even reduce the medical staff’s ability to serve patients.

    Air Conditioning

    Providing optional standby power for air conditioning systems can be expensive, since the required generator capacity is increased significantly. However, there are many cases where the loss of air conditioning can be very disruptive for commercial operations, and the extra cost may be justifiable from the business standpoint. For example, the loss of air conditioning can ward off potential customers in restaurants and retail stores.

    Tags Design | Building Code | new york

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