For a small segment of the population, such as designers and installers, building electrical and mechanical rooms are fun to tour. Although sometimes skilled construction trades make works of art, most buildings exist for people rather than systems. There is a balance between enough MEPFPT square footage to meet the need, but not too much that the utilities over-claim space useful for people. Does the building even require a dedicated electrical room? Beyond an owner’s preference for safety and security, building codes dictate if an isolated electrical space is required. At standard building voltages less than 600V, enclosed equipment can usually be located in public spaces as long as adjustable trip units on circuit breakers are lockable. Instead of dedicated electrical space, a section of or an entire building might be served by wall surface or recessed mounted panels not enclosed in a room.
Life Cycle of an Electrical Room
To right-size an electrical room requires considering the life cycle of the building. It is not uncommon to have aspirations to design 50-year buildings. By charting this path, the team takes on the responsibility of reviewing how the electrical room will change over time, as power electronics typically have a 30-year life span. Owners with aging equipment rely on refurbished parts and veteran technicians. After this period, manufacturers might not support the maintenance of old components. In addition to the manufacturer’s documentation, references such as the National Electrical Contractors Association (NECA), National Electrical Testing Association (NETA), and National Fire Protection Association (NFPA) 70B provide maintenance insights. Reliability-centered maintenance strategies increase system up-time and promote safety.
Is there a plan for how the activity will occur at the future refresh cycle of the electrical system? Downtime might not be an option in the mission-critical and healthcare-type market sectors. Also, the electrical system is not the only building system requiring a refresh cycle, so forward-thinking value-add measured designs include spare conduits, knock-out walls, or similar features.
- Initial Construction: the room design needs to be constructable and be considerate of construction activity
- Normal Operations: electrical rooms are visited to turn power off/on or isolate the system circuits
- Maintenance: regular maintenance activities are required by product listings, laws, insurance, and to avoid unexpected outages
- Renovations: from small to large, as well as planned and unplanned, buildings change over time
Types of Electrical Rooms
There are a few different types of electrical rooms. Less common are energy storage (batteries, capacitors), engine generator rooms, and vaults (required 35kV+); each has further requirements outside the scope of this blog post. Otherwise, for buildings the two basic types of electrical rooms are stated to be “normal power” and “emergency power” rooms. Projects that include lighting inverters over 500VA (NFPA 111) or back-up generation (NFPA 110) might need an emergency electrical room.
Site Considerations
For greenfield and renovation building projects, beyond project-specific characteristics, there are general considerations for locating electrical rooms. The site selection reviews aspects such as flood plain, soil bearing capacities, and seismic conditions. Medium commercial, institutions, and industrial customers first consider locating the service transformers outside or indoors. The total site volume of transformer oil and other environmental considerations are important for large sites (EPA, CFR). If liquid transformers are determined to be located indoors, depending on the type of building construction, they might need to be located away from walls and columns and might influence fire protection strategies. Some projects might be phased over time, energizing new electrical rooms as needed. If the electrical system is to be considered reliable, to support a fire pump, for example, per NFPA, the incoming utility is not overhead but well protected.
Locating Electrical Rooms
The location of the electrical rooms within the building can be easily overlooked on-paper. Installers of systems receive puzzles and hopefully, designers were thoughtful when considering the electrical room locations within the building footprint. Although code-minimum would allow so, best practice avoids combining electrical rooms with mop closets. One of the primary factors for locating electrical rooms is based on the load concentrations. For example, the project will benefit if electrical rooms are located near data centers, auto shops, kitchens, and other spaces with higher power demand. Locations like office cubicle farms have many connections, but the electrical demands are low and rarely exceed capacities.
The picture gallery below shows various floor plan options for potential electrical room locations. This collaboration occurs during the Schematic Design (SD) project phase. Click through using the arrows to view four options for discussion.
- Option A is nice because the room is located near a fixed building component, the stairwell, not subject to future renovations; although, depending on the rest of the floor plan, the staircase wall being blocked for existing circuits from the electrical room might be limiting.
- Option B is not ideal, as two walls, the shaft and elevator, reduce flexibility to exit the room with circuits; note an elevator machine room would also hinder conduit routing, since code prevents passing through them.
- Option C shows the electrical room being adjacent to the technology closet, which is ideal if transformer EMI interference is considered and allowed by relevant standards. Ideally, the rooms stack and avoid significant structural members for easy routing of conduits.
- Option D demonstrates that other larger building systems have corridor routing needs. Although contractors have enhanced software tools to aid coordination, locating the electrical room to reduce installation congestion is preferred.
Electrical Room Construction
Ceiling
Traditionally, to make it easier for installers and to save project cost, since electrical rooms are non-public spaces, they skip the ceiling (open to structure). Although, some modular construction methods are compartmentalizing entire rooms. Having an open ceiling is more flexible for installers. For example, designers of UPS systems and other high demand equipment avoid directing the contractor to install conduits underground; this helps to not derate the cable ampacities, so the open ceilings provide area for conduit routing.
Walls
Sometimes forgotten by the designer as they draft on the computer, equipment clearances need to allow for depth to mount plywood and unistrut. Designers work with architects to situate the walls of the electrical room to avoid large structural members, such as in multi-floor buildings with electrical conduits traveling between floors. The walls of electrical rooms have minimal requirements for fire or smoke ratings. The common driver for rating walls is for emergency electrical rooms or due to transformer type or capacity (kVA).
Doors
Doors. Architectural partners help coordinate the quantity and number of doors. Design staff will highlight when the door swing direction makes a difference or when panic hardware might be needed (NEC).
Floor
Floors for electrical rooms must consider weight when transformers or UPS systems are to be installed. Raised access floors or below floor conduits involve coordination with the equipment shop drawings. A common coordination item involves the sweep of conduit elbows or cables, as limited by code. For example, the code might require a particular burial depth or the radius sweep may influence depth and exact equipment placements in the space. Electrical room floors might also contain code-required curbs for thru-floor busways. Many installations provide equipment pads, although if water concerns are low, eliminating pads saves cost and allows installation flexibility.
Support Systems
As electrical rooms house passive and active heat generating equipment, manufacturers list ventilation guidelines such as keeping a distance away from walls or providing mechanical heat loss solutions (powered cooling or exhaust). Due diligence is required to find the right locations for electrical rooms within a building footprint.
Floor Plan Layout
After locating the area where the electrical room will be in the building, the design team starts making a floor plan layout. As clients prefer to bid projects competitively, design teams write specifications with multiple manufacturers eligible to bid. Thus, layouts of electrical equipment rooms are commonly approached by using the worst case dimensions across all potential manufacturers. Certainly, there are efficiencies possible if the manufacturer of the equipment is known ahead of time.
In addition to fitting the systems into the electrical room, consider if medium voltage or otherwise large junction boxes are needed. A freestanding unistrut system may be constructed to hold equipment, or if thoughtfully done, dry-type transformers might be stacked. Designers and installers should collaborate with owners to ensure a path through the building to remove and replace equipment over the life cycle of the room.
Operations and Maintenance
Owners promote maintenance by posting safety signs and 1-line drawings of the systems in main electrical rooms. These types of considerations are useful during the design, such as if the owner plans on performing Infrared (IR) scanning or needs space to utilize a hot stick. In medium voltage applications a breaker cart and racking operations are also a consideration. Potentially, the electrical room has cam-lock connection points for attaching a load bank or temporary generator. Maintenance and operation team considerations brought forward during the design phase also helps ensure adequate storage in the buildings for cleaning and other supplies. Otherwise, risk the electrical rooms being used as storage.