Flexible vs. Traditional

Traditional conduit-and-wire busway systems have always dominated engineering specs. But more and more, flex-busway systems are being installed for certain types of facilities, thanks to a number of benefits. Specifically, flex-busway fulfills the flexibility and power density requirements for server/computer rooms, manufacturing plants and assembly facilities.

By David Pickett, P.E., Senior Vice President, Interface Engineering, Inc., Portland, Ore. March 1, 2004

Traditional conduit-and-wire busway systems have always dominated engineering specs. But more and more, flex-busway systems are being installed for certain types of facilities, thanks to a number of benefits. Specifically, flex-busway fulfills the flexibility and power density requirements for server/computer rooms, manufacturing plants and assembly facilities.

These systems range from 60 amps to 225 amps, in contrast to traditional busways, which typically range from 225 amps to 5,000 amps. Depending on the vendor, flex-busway systems have either a continuous slot for plug-in units or plug-in access points available on 12-in. centers. Compare this with traditional plug-in busway systems, which have plug-in access on 24-in. centers.

A wide range of accessories is also available from the flex-busway manufacturers for the plug-in units, including factory-made cord drops with user-specified NEMA receptacle configurations. The use of plug-in cord drops provides a great deal of flexibility in the system. The smaller amperages available, the high density of plug-in access points and the wide range of factory accessories are three advantages to replacing traditional wiring methods with flex-busway in high-density power applications.

When compared to a conduit-and-wire system, one major advantage of flex-busway systems is labor cost. While it’s true that the material costs for conduit-and-wire can be less, the labor cost is much higher. These costs include conduit installation, box installation, wire pulling and receptacle installation. And as the density of connected loads increases, the labor costs for conduit-and-wire systems increases dramatically. One of the biggest labor-saving items with flex-busways are the factory plug-in cord drops, which eliminate the field labor required to install branch circuiting. Utilizing these plug-in cord drops also provides for future savings as equipment is moved or added.

In fact, additions and relocations for cord drops are fast and simple with flex-busway systems. For example, if equipment is re-located, the cord drop can easily be unplugged from the flex-busway and moved along with the equipment. And adding new equipment is as easy as plugging in a spare cord drop. Changes are made in a matter of minutes—without any power shutdowns. In contrast, with conduit-and-wire, the same kinds of changes and additions would require a significant amount of labor. This could include adding conduit, adding breakers to panelboards, routing homeruns to panelboard, pulling wire, adding support for cord drop, and finally, wiring the cord drop. What’s more, the initial installation of the flex-busway is normally less expensive, depending on the number and density of cord drops. The higher the density, the more economical it becomes.

For example, as mentioned at the outset, an excellent application for flex-busways is in server/computer rooms. These facilities have a very high density of receptacles and power. A typical design requires two receptacles at each rack. Racks are approximately 24 in. wide. These receptacles are traditionally fed by conduit and wire running below a raised floor or overhead. To support this high density of circuits, additional panelboards are needed for the breakers. Maintenance or additions in this type of system require removal of raised floor panels and potentially shutting down the branch panels to install new circuits or receptacles. Using flex-busway in this application would greatly reduce the labor time for the initial installation and also reduce costs for future maintenance. Also, adding new cord drops can be done without shutting power off, thereby avoiding downtime for computer network systems.

Another benefit of using flex-busway is that since the overcurrent protection for the receptacles at the racks is distributed along the busway, panelboards can be reduced. This saves more labor, floor space and material costs.

Working it out

But while there are many points in flex-busway’s favor, there are coordination issues that cannot be ignored when applying this technology to server/computer rooms. The first is making sure that end users approve of the appearance of overhead busway. It’s not uncommon for IT professionals to desire their server/computer rooms to have a “clean” appearance.

Another issue is coordinating with signal cable tray routing. However, this is not always a negative. Consider utilizing the same structural support system of the cable tray to support flex-busway. This also saves on time and materials. Other types of equipment that flex-busway must be coordinated with include HVAC ductwork, lighting systems and fire-protection systems.

In cases where there are workstations with small tools or equipment that require plug-in type of loads of 60 amps and smaller, flex-busway is the power distribution method of choice.

In addition to computer rooms, other popular applications for flex-busway are assembly and manufacturing facilities. This is especially the case for spaces that are not using heavy machinery. If heavy machinery is being used, traditional busway is the better application because it can handle larger single-point loads.

One trend that most electrical engineers have on their minds these days is sustainability. Here, too, flex-busways help solve a problem. Because of the difficulty of reconfiguring conduit-and-wire systems in order to meet the needs of a remodeled space, the original wiring system is normally scrapped and new materials are installed.

Flex-busway, in contrast, is much more likely to be reconfigured or salvaged. If the space is just being reconfigured for the same use, it is easy to relocate the flex-busway to the new layout of the space. In the event that the space is being changed to a different use and busway will no longer be applicable, then the busway system can be easily removed and salvaged for reuse in another location.

When selecting a flex-busway system, be aware that there are differences between manufacturers. Things that need to be considered are housing material, bus material, bus configurations, voltage availability, dimensions, accessories and the variety of plug-in unit options. One major difference to be aware of is plug-in access points, as most manufacturers only have plug-in access points on 12-in. centers, which are actually staggered on 24-in. centers on both sides of the busway. These access points are located on the sides of the flex-busway, which can complicate the layout of the equipment. A couple of the manufacturers have a busway with a continuous slot on the bottom, which provides greater flexibility and density of outlets. These types of flex-busways also can be used to support and feed luminaires that are designed specifically for the system.

Adding it up

In general, depending on the density of circuits and receptacles, flex-busway can be very competitive in cost. But for each application, a cost/benefit analysis should be done to determine if flex-busway is a suitable option. Consideration should also be given to equipment density requirements, potential future equipment, frequency of space reconfiguration and frequency of equipment relocations and additions.

With the many advantages available—flexibility, sustainability and labor savings—expect to see flex-busway systems being applied to more and more facilities.

Flex-Busway Pros


Easy to reconfigure

Savings on installation costs

Sustainable benefits

High density of plug-in access points

Higher available amperages