Let's further explore the considerations of Distribution Pathways and Local/Branch Equipment Rooms when designing MEP spaces.
Distribution Pathways
Distribution pathways are needed for interconnecting all the electrical equipment and end-user devices, and the pathways will affect where rooms are located. Conduits can be routed above the equipment, below ground, or in the ceiling space of the floor below, though overhead conduits need space within the rooms to leave the equipment and transition to the desired route going to other parts of the building (see picture below). The routing of the feeders and how they enter/exit the distribution equipment must be evaluated during design and reconfirmed during the shop drawing review, as this will impact how the equipment is constructed and affect its physical size.
Conduit pathways need to be considered when designing electrical rooms to ensure proper clearances are met and that the distribution is efficient.
Below grade conduit routing needs to be coordinated with other utilities and footing/foundation elements. The restrictions that these place on the routing may impact the layout of the equipment in the room and the size of the space needed. Similarly, beams on the floor above or below the equipment may require an offset of conduit or shifting of the equipment to allow for the conduit installation to effectively occur.
Horizontal pathways can define the placement of electrical rooms, as other building elements may impede these routes and affect installation. Structural beams and large ductwork can become obstacles, especially in tandem with high ceilings. Large-volume spaces like gymnasiums and atriums require extra care as to how conduit will be routed across or around these areas, especially when the entering/exiting pathway would be lower in elevation than the ceiling.
Vertical risers are typically accommodated in either one of two ways—through shafts (pull boxes may be required depending on the height of the building and conduit layout) or stacked electrical closets. Stacked closets allow for the busway or conduits that distribute power throughout the building to be run through these spaces for a more efficient and less expensive installation. If these closets are constructed with 2-hour-rated partitions, the stacked rooms can provide the code-required circuit protection for EPSS feeders and fire alarm circuits without having to rely on more costly wiring methods.
Local/branch Equipment Rooms
A third space type, the local/branch equipment room, is often referred to as an electrical closet (see picture below). Distribution panels, branch circuit panels, and low-voltage transformers are typically located in these spaces and directly serve the end-user loads: lighting, receptacles, and small equipment. Lighting control system panels and devices (and other electrical system devices) are sometimes also located in these rooms. Given the amount of change that occurs in buildings over their lifespan, extra wall space should always be provided in these rooms for future equipment.
The electrical closet is arranged to meet multiple requirements. First, all code clearances have been met. Additionally, it provides a vertical pathway for feeders extending up through the building.
In multistory buildings, these spaces should be stacked. The placement of electrical closets within a building’s footprint is often an item of much debate and discussion with the rest of the design team. The NEC has set restrictions on piping and ductwork routed through these rooms (i.e., dedicated spaces). Conduit needs to be routed out of the room to the floor or area served; minimizing branch circuit lengths help avoid excessive voltage drop and reduce distribution costs. These rooms should be located as close to the center of the area served, with conduits routed out in all directions.
Avoid specific adjacency to other building elements. Often, closets are targeted for location next to mechanical shafts, but the need to get duct-work and/or piping out of these becomes challenging and conflicts with the electrical equipment’s dedicated space. Similarly, locations next to stairs or elevator shafts present other challenges and limit the routing of conduits out of the electrical rooms. Locating electrical rooms next to these, especially if placed between, should be carefully evaluated to ensure there is enough space and flexibility for conduits.
Additional Space Needs
Outside of working- and dedicated-space needs, there are many special considerations for electrical rooms that depend on building programs as well as exterior spaces that will directly impact how the electrical systems are designed. The needs and expectations associated with an office building are very different from that of a data center or hospital with regard to the electrical distribution systems. Redundancy and resiliency are essential for mission critical-type facilities. Flooding due to natural disasters is a key element in determining equipment placement. These equipment should be located above the anticipated flood levels. This ensures ongoing continued operations during and after an event.
Mission critical and safety-critical installations require added redundancy to ensure the continuity of business operations. Redundancy of systems requires more space, as the equipment is separated into different rooms in different parts of the building. Having panels that are part of a redundant distribution arrangement (A and B sources) located adjacent or in close proximity to each other in the same electrical room greatly minimizes the value that the intended redundancy offers. The redundant equipment should be located in separately rated spaces, with the A sources and distribution located apart from the B sources and distribution.
Additional clearance requirements include allowing for future equipment to be moved into a room or allowing for the eventual replacement of that same equipment. While code may only require 3 or 4 ft of clearance in front of a piece of equipment, the physical dimension of the equipment could be larger. Because of this, the only way to effectively remove and reinstall a replacement is to leave an area that is larger than the footprint of the equipment.
Getting equipment from the exterior of a building to its final location may not always be a concern during the initial building construction, but it will certainly be an issue during later time periods of equipment modifications, additions, or replacement. The entire pathway from the building exterior, including doorways, may need to be enlarged due to the height or width of the equipment. If the equipment is located on a floor level that is below- or abovegrade, then area wells, reinforced floors, and a pathway or removable sections of the exterior wall assembly may be required.
Buildings are expected to have a life well beyond the initial install, and yet future growth and conduit installation are rarely considered. This automatically infers change, which will likely come in the form of added equipment and conduit. Initial planning and system design should account for this by including spare breakers, additional distribution sections, and oversized-conduit rack supports.
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SMA connects IT, Facilities and Design. For the Data Center Design Consideration, please visit
(1) Site Selection,
(2) Space Planning,
(3) Cooling,
(4) Redundancy,
(5) Fire Suppression,
(6) Meet Me Rooms,
(7) UPS Selection,
(8) Raised Floor,
(9) Code & Standards,
(10) Transformers and Harmonic Distortion,
(11) Multi-mode UPS Systems, and
(12) Electrical Rooms (I) and (II)
All topics focus on key components and provide technical advice and recommendations for designing a data center and critical facilities.
