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Electrical Room Design Requirements and Considerations



When designing main electrical and sub electrical rooms, there are many factors that need to be considered. Space is always the main concern, but equipment location, foreign equipment, and future needs are all also important. The following will explain different considerations when an electrical room is laid out and how the electrical design engineer can best coordinate with architects, as well as mechanical, plumbing, and fire protection engineers.


Working Space vs Dedicated Space

One of the main confusions when it comes to electrical equipment is the difference between working space and dedicated space. According to NEC 110.26, working space (also referred to as ‘clearance’) applies to the protection of the worker, and dedicated equipment space applies to the space reserved for future access to electrical equipment and to protection of the equipment from intrusion by nonelectrical systems. In laymen’s terms, working space is typically viewed as the space in front of a piece of electrical equipment, while dedicated space is the space above the equipment.


Depth of Working Space

The working space depth refers to the distance in front of electrical equipment that is required to be clear. This value depends on the equipment voltage as well as several conditions. Table 1 and its accompanying condition definitions show the depths for different situations.

Working space shall not be required in the back if rear access is not needed to work on the equipment. If rear access is required, then a minimum of 30” of horizontal working space shall be provided.


Condition 1: Exposed live parts on one side of working space and no live or grounded parts on the other side of working space (wood and drywall are good example of non-grounded parts)

Condition 2: Exposed live parts on one side of working space and grounded parts on other side of working space (concrete, brick or tile walls considered to be grounded)

Condition 3: Exposed live parts on both sides of working space (panelboard is an example of an exposed live part)


Width of Working Space

The width of the working space in front of the electrical equipment is the width of the electrical equipment or a minimum of 30in; whichever is greater. For example, most panels in a sub electrical room are about 18” wide. This means that their working space width would be 30” since this is the minimum required by the NEC. If a piece of equipment is larger than 30” (think main switchboard or large distribution panel) then the width of the working space would be equal to the width of the equipment. The 30” measurement can be made from either the left or right edge of the equipment and can overlap other electrical equipment clearances, refer to Figures 1 and 2 below.




Figure 1: Equipment clearances measure from left edge, center, and right edge



Figure 2: Overlapping of working space




Height of Working Space

The working space shall extend from the floor, grade, or platform to a height 6’6” or the height of the equipment, whichever is greater. Other equipment associated with the installation installed above or below (meter, wire troughs, etc.) are permitted to extend 6” into the working space, but no more.


Figure 3: Height of working space



Electrical Room Coordination

When large electrical equipment (1200A or more and larger than 6ft) is located within an electrical room, there shall be an entrance to and egress from the working space 6’6” wide at each end of the room. So, any time there is this size equipment in an electrical room, there must be two doors. But, of course, the NEC has plenty of exceptions throughout its 1200+ pages and this requirement is no different. A single entrance shall be permitted if there is unobstructed egress (see Figure 5) or there is extra working space which is defined as double clearance. So, if your equipment requires 4ft of working space clearance in front, but is located in a room with 8ft clearance, then the room only requires a single egress door.









Figure 4: Double entrance and egress illustration




Figure 5: Unobstructed egress


Personnel doors that are less than 25’ from the nearest edge of the working space shall open in the direction of egress and be equipped with listed panic hardware if the room contains electrical equipment rated 800A or above. You will typically see this condition in main electrical rooms and sub electrical rooms that require large distribution panels.

The dedicated equipment space above electrical panels, switchboards, switchgear, and motor control centers shall be free of foreign systems. This space is equal to the width of the equipment and extending from the floor to a height of 6ft above the equipment or to the structural ceiling, whichever is lower. Foreign systems are defined as sprinkler pipes, ceilings, ducts, etc. Suspended ceilings with removable panels are permitted to be within the dedicated equipment space. The space above the dedicated equipment space is permitted to have foreign systems if they are provided with protection to avoid damage to the electrical equipment from leaks, breaks, or condensation of the foreign system. Sprinkler piping is the one exception to this rule. It can enter the dedicated space if it is provided with the aforementioned protection.



Figure 6: Example of dedicated equipment space



As an architect, mechanical engineer, or plumbing designer, the next time you encounter an electrical room refer to this article. It can be a quick guide as to how your equipment is permitted to be installed within the vicinity of electrical equipment. For an architect designing a building or space, it can be a good reference as to how big you need to design a main electrical or sub electrical room. It will also tell you whether you need multiple egress paths or additional equipment for your doors.

Feel free to reach out with any questions or comments! Wilde Engineering is here to help!

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