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Architectural Considerations for the Installation of an Emergency Generator

Posted by: William Stewart on Wednesday, August 31, 2016


The decision to provide an emergency power supply system for your project will necessarily require distinct considerations by the entire project design team. An emergency power supply system (EPSS) consists of a standby engine-generator unit (genset), automatic transfer switch(s) (ATS’s) and associated switchgear (circuit breakers and disconnects). In many instances, such as high rises, health care facilities, public schools and emergency shelters, etc., the code requires life safety and supporting systems connected to on-site back-up power. Furthermore, the building owner must determine the cost effectiveness of back-up electrical power necessary for reliable business operations and/or mitigating any loss of production capacity. Regardless, the implementation of on-site emergency power generation is unique for each application and will require significant planning from the outset of the project design.

If the genset is to be out of doors, a location must meet the code requirements of a minimum five feet (5’) from the building, is aesthetically and odorously acceptable (away from building windows, neighbors, etc.), accessible for maintenance and fueling, secure, and conforms to noise level ordinances. Generally, a packaged genset with a weather enclosure and critical exhaust muffler, on a concrete pad, is sufficient for exterior applications. It is recommended the pad extend beyond, and any screen walls be, a minimum of four feet (4’) from all sides of the genset to allow for maintenance. Additionally, when screened in, openings for louvers, etc. may be necessary to meet the genset manufacturer’s airflow requirements. Finally, a base mounted fuel tank will increase the overall height of the installation, whereas as separate fuel tank will require more yard space.

When the genset is to be located inside the building, additional considerations should be coordinated in the design phases. The room must be fire rated for two hours (2 hrs) and sized as determined by the genset selected (including the 4’ clearances) with openings to the exterior for ventilation and exhaust airflows and a ceiling height to accommodate the unit with base tank (if applicable). Also allow enough headroom for the insulated exhaust/muffler piping and proper unit servicing. Additionally, the genset should be located as close as practical to the main electrical equipment for installed cost considerations, as well as, to facilitate maintenance. Finally, no other equipment or building systems shall be located in this room including piping, ductwork, etc., unless necessary for the proper operation of the genset.

The ATS signals the genset to start upon loss of normal (utility) power and will connect the generator to the designated loads. Depending on the type of installation, two or more ATS’s may be required. Automatic transfer switches can be quite large, taking up considerable floor and wall space. Also, for life safety systems in excess of 1,000A and 120V to ground, the associated life safety switchgear must be separated from the normal switchgear by a one hour (1hr) partition.

The requirements for an emergency power supply system are unique for each installation and require careful planning by the design team. A thorough code review, as well as the owner’s cost benefit analysis, should determine the necessary connected loads. As the EPSS requirements are developed, equipment may be selected and the design team can optimize decisions regarding the location and size of the installations.

Exterior Mounted Genset in Weather Enclosure


Genset Installed Inside the Building Envelope


Exterior Mounted Fuel Tank