Addressing Electrical Space Requirements in Modular Energy Plant Design

“Sure, we have plenty of space….”

Often times that is the response we receive when we have to add equipment to an existing, or nearly complete design.  While there may be physical space for the equipment in question, the space requirements imposed by the National Electrical Code or other regulations around electrical equipment often make a seemingly ample-sized space just too small.  Some reasons for regulatory requirements for space around electrical and other equipment include: means of egress from an enclosed space in the event of a fire, door swing clearance for protection of personnel, electrical working clearances for the protection of electrical workers, fire safety equipment access (such as fire extinguishers), and equipment operational space where manual manipulation of equipment is necessary for operations personnel.

“But all that space around the equipment is just wasted…”

Electrical installations, as with many other systems, are often forced into smaller and smaller spaces due to real estate, cost, or practicality reasons.  This is evidenced in any large city that can noElectrical Controls for Modular Energy Plant longer increase its physical footprint and must build upward; or make more efficient use of the existing space available.  Likewise with modular packaged systems, there is a practical size limit to how large the footprint may be.  Ingenuity and efficiency in design must be drawn upon during execution of these solutions and electrical design is no different than other disciplines in the design process.

There are many choices an electrical engineer must make with regard to minimizing equipment layout space in order to achieve the most efficient orientation of equipment within a modular unit.  While our business focuses heavily on modular Turbine Inlet Air Chiller (TIAC), data center cooling and District Cooling systems, these same design choices can be beneficial in many electrical applications.    Different configurations can be employed to achieve space efficiency and the benefits of several configurations are discussed here.

Front Access Equipment

Many manufacturers offer equipment, such as switchgear or Motor Control Centers (MCCs), with a front-access-only feature.  This feature allows all maintenance and service operations to be performed from the front of the equipment, eliminating the necessity of rear access, and therefore the requirement for working space behind the equipment.  Opting for front access equipment allows placement against a wall within the electrical room and reduces overall space requirements compared with center-of-room placement of equipment because clearance behind the equipment is no longer required.  The advantage of this solution is that valuable space savings can be achieved by reducing the overall footprint of the electrical room, and thus, the whole modular solution.

Shared Clearance Layouts

Another option made available with front access equipment is a shared clearance layout.  With this configuration, electrical clear space efficiency can be realized by placing electrical equipment on opposing walls of the electrical room, facing each other.  The NEC clear space requirements for electrical equipment facing each other is not additive.  That is, if the equipment clearance requirement for each individual assembly is three (3) feet, placing them facing each other does not increase the clearance requirement to six (6) feet.  It is generally significantly less than the additive distance because the NEC recognizes the impracticality of both assemblies being serviced simultaneously.  Sharing clearance with other reserved spaces, such as means of egress, door swings, or fire protection equipment are some additional options for reducing overall electrical room footprint, as long as the NEC (or any other local) requirements are observed.

Back-to-Back Configurations

Many times it is not practical to split electrical distribution equipment into smaller units and locate them along the walls facing each other due to feeder or shipping split considerations.  In these cases, a back-to-back configuration of the equipment may allow for equipment to be located in a shorter room than an in-line layout or allow for the colocation of the electrical gear on the same module base as the equipment being served by the electrical gear.  While the electrical room will still need to be wide enough to allow clearance for both fronts of the electrical equipment, a shorter lineup of equipment can be achieved.  This arrangement may also allow for the electrical distribution gear to be located on the same module as the equipment being served; allowing for factory wiring of the electrical loads.

Rear Access HatchesElectrical Controls for Modular Energy Plant

There are occasions where rear access equipment is the best choice for an installation; but there just isn’t enough space for the required electrical clearance behind the equipment.  One option that may be available to the engineer (and it lends itself very well to modular design) is the locating of the rear access equipment against an exterior wall.  The exterior wall behind the electrical equipment is provisioned with removable access hatches to allow access to the rear of the equipment for maintaining and servicing the gear.  Where this design is incorporated, clear space must be provided outside of the module, and the hatches must be at least as large as the panels or doors on the back of the electrical equipment being accessed.

Stacked Configuration

For quite some time, manufacturers of large distribution equipment have been taking advantage of space savings by stacking devices within their gear.  MCCs use a modular, stacked configuration in order to maximize floor space.  Medium voltage switchgear manufacturers offer motor control switchgear lineups utilizing “two-high” configurations.  And, in the modular design atmosphere, some types of equipment are small enough that they may be mounted in an over-under orientation without violating code requirements.  Some types of equipment which are often found in this orientation include: small transformers, lighting panelboards, receptacles, junction boxes, or lighting controls.

Being creative with the layout of equipment, both large and small, can have a significant impact on electrical room space requirements.  With a limited footprint requirement for a modular TIAC or modular utility plant solution, keeping the electrical system reserved space small to make way for the larger process equipment is a necessary move.  Small can still meet code clearance requirements if proper attention is placed on the design.

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