Generator Set Rooms & Enclosures

Electrical Room Space Requirements

The space requirements for standby and emergency power systems do not rank at the top of an architect’s design list. Consequently, service personnel can find themselves in tight quarters when these power systems are jammed into areas that meet only minimum safety requirements and don’t take service- ability into account.

Building service equipment must have an advocate early in the design process. It is far easier and less expensive to plan for adequate space in the design phase than to compromise on unit size and retrofit equipment to fit in cramped areas.

Basic Room Requirements

Minimum requirements set for the National Fire Protection Association (NFPA) in the National Electric Code (NEC) is that a person must be able to complete service duties with enclosure doors open and for two people to pass one another. If maintenance must be done at the rear of the cabinet, similar access space must be available.

The NEC also requires 3 to 4 feet (1m to 1.3m) of aisle space between live electrical components of 600 volts or less, depending on whether live components are on one or both sides of the aisle. This requirement holds even if components are protected by safety enclosures or screens.

Installations over 600 volts require even wider aisle space, from 3 feet (1,) to as much as 12 feet (4m) for voltages above 75kV. Service rooms with 1,200 amps or more require two exits in case of fire or arcing. Because transformers vary, make sure minimum wall clearances are met as specified by the manufacturer.

Specific rules and exceptions are spelled out by the NFPA in its recently revised NEC rules.

Gen Set Space Needs

Caterpillar recommends floor space between an engine and parallel wall space or another gen set should not be less than the width of the engine. Overhead, there should be enough space allocated to allow convenient removal of cylinder heads, manifolds, exhaust piping and any other equipment for service. Consider specifying enough room for a chain hoist or overhead crane. Space fore and aft of the engine should allow camshaft removal.

Batteries to start gen sets should be kept as near as possible to the engine to avoid long energy robbing cables. The fuel tank should be located near gen sets to prevent long fuel line runs which can tax fuel pumps. Access to this equipment for service must also be considered in the design phase.

Switchgear Considerations

Controls and switchgear are best housed in a separate air-conditioned room next to the gen set with a window into the engine room. Switchgear that can’t be placed in a separate room should be located to take advantage of incoming air to cool the switchgear.

Consider Remote Options

Many times, building demands for emergency power increase so dramatically that the standby facility out grows the space it was originally allocated. Consider the following remote options.

  • Remote radiators. Radiators mounted on rooftops or inconspicuously at ground level outside can open up floor space and help lower room temperature when gen sets are in operation.
  • Remote switchgear. Switchgear placed in another service area near the gen set room opens floor space and helps keep operators out of high decibel areas when gen sets are in operation.
  • Stand alone packages. Here, the total gen set installation is moved to separate building or a stand alone packed is utilized. Stand alone, self contained units can be equipped with removable wall sections that allow for gen set maintenance and repairs.

Generator Set Enclosures

There’s increasing pressure on every designer to squeeze more usable space out of building in the design phase as well as those already in place and undergoing renovation.

That often puts gen sets in an awkward position: In new building, architects vie for that space for other uses. And in renovation projects, the power upgrade also means that additional standby power is needed, and the larger gen sets and switchgear won’t fit in the original space.

That’s led to the development of outside enclosure for gen sets. Designers are finding that moving gen sets outside takes more tan pouring a slab and putting a steel-sided housing over the structure; it entails many factors that affect gen set operation, safety as well as local code requirements for sound, sight and air quality.

Caterpillar and CAT dealers across North America have addressed site, sound and code requirements for thousands of gen set installations. This experience has led us to develop some innovative practices to enclose gen sets so they do not greatly affect the surrounding area. Following are criteria that must be considered with every gen set enclosure:

Space and System Requirements

The enclosure should offer as much or more space as required by the gen set in a building. In fact, because enclosure square foot cost are lower than in a finished building, you will likely have more funds available for enlarging the enclosure space. EPG Designer as well as AutoCAD drawings available from your CAT dealer cite minimum clearances needed. The enclosure should offer expandable construction, withstand excessive winds, allow full service access to gen set, including the ability to lift the enclosure off the installation.

When selecting a site for the enclosure, consider cfm air requirements for the gen set(s) as well as how exhaust fumes may travel. Pay particular attention to building ventilation inlet locations. Finally, consider the system’s needs for fuel storage, cooling, monitoring and maintenance. Fuel tanks can be built into enclosure bases, and is an option on the drop over enclosure- available from Caterpillar.

Enclosure security is another concern. The enclosure must be lockable and tamper and vandal resistant.

Service Considerations for Gen Set Installation

Gen sets and electrical control equipment often do not get the space considerations required to ensure a proper installation in a building. Or at least it seems that way as architects design new buildings that offer tenants as much usable space possible.

It’s a touch act to balance gen set space needs with other building service functions. But if you keep routine maintenance, future equipment repair needs and expansion considerations in mind, you will be able to offer your client an installation that allows the gen set to perform efficiently and reliably for years to come.

The illustration below shows several factors to consider in engine room design. Here are some other considerations:

The Generator Room

Look down the road to the day extensive gen set repairs may be needed. Even the most reliable gen set, after thousands of hours of operation, will need some internal work. Will there be enough room for engine or generator disassembly? Can the unit be removed without major building alteration? You may want to specify a chain hoist or overhead crane into the room’s design for these heavy chores.

Gen Set Support Systems

Does your room design consider how add-ons such as cogeneration equipment or remote cooling systems may obstruct service of components? A remote radiator with properly routed plumbing can significantly simplify engine service and disassembly. Strategic placement of auxiliary tanks can make service checkpoints ease to find and maintenance quick to complete.

As Environmental Protection Agency (EPA) regulations tighten on underground fuel tanks, consider requirements aimed at making fuel tanks leak proof. Above-ground diesel storage tanks or other fuels (natural gas or propane may be viable alternatives.

Look at how you gen set installation gets its air. It needs a clean, relatively cool and plentiful supply. Massive ducting should be routed with as few bends as possible, and not interfere with service sites on the gen set.


Power demand will likely grow long after clients have moved into the building, so the need for more electrical service is inevitable. Does your plan allow for such growth? Remote gen set switchgear is one option that can open up space in crowded installations.

Sound Attenuation

Controlling noise emissions is the greatest challenge for enclosure designers. Tougher local codes are cracking down on high sound levels. Several methods can be employed to minimize sound transmission: Caterpillar offers sound attenuation packages that can reduce sound levels to 72dB(A) or 85 dB(A) at 50 feet. If you have even lower dB(A) level requirements, we can develop special enclosures that can meet your needs.


Because enclosures often are in the public eye, they should blend in with the surrounding environment. The enclosure should look clean, neat and be maintenance free. For example, CAT Drop over Enclosure are built with 12 gauge coated steel and painted with a 2 mil thick baked polyester powder. All parts are painted before assembly, assuring good coverage and years of corrosion free service.

Code Requirements

Various city, state/provincial and federal codes affect gen set enclosure. Enclosures may be considered temporary to permanent buildings, depending on your zoning code.

Consider sound, sight, and earthquake tolerance requirements. Food and health codes may also impact enclosure location and design.

Proven Technology

Caterpillar and CAT dealers have developed several types of enclosures for various gen set installations. This experience has helped us find out the most efficient, economical way to supply enclosures that meet engineering design and sound attenuation requirements most often requested by customers.

Contact us for a complete overview of our enclosure capability.