Overhead power distribution in manufacturing

When designing manufacturing facilities the method of power distribution is a subject that comes up early and often. The one nearly universal requirement from the owner is flexibility to be able to accommodate changing power distribution needs due to changes in equipment and equipment locations. For those owners with specific long-term needs then underground distribution may be an option but I will neglect this option for this brief summary. I will also neglect large facilities using sub floors and interstitial spaces.

The (3) common choices are conduit, bus duct, and cable tray. All have been used successfully over the years and all have inherent advantages and disadvantages.

Lets start with traditional conduit systems. Distribution panels are typically located throughout the manufacturing floor or possibly in centralized locations. From that point the individual branch circuits are fed to the equipment in overhead conduit runs. Conduit is typically supported with unistrut trapeze systems.

Advantages: Simple to specify and install.

Disadvantages: Conduit and branch circuits can’t be reworked or reused without modifications to the conduit systems.

Next we have bus duct which is supported overhead, comes in various ratings through thousands of amps, and can be routed in different directions as needed. Fused switches or breakers are installed in the bus duct as plug-in modules and from those switches power is connected to equipment by cord or conduit runs.

Advantages: Provides large quantity of power above the manufacturing floor.

Disadvantages: High initial capital investment, high weight load, capacity often goes under utilized, poor choice in areas congested (or potential to be congested) with other systems, can’t be easily modified.

Lastly, we have cable tray which can be used to support power cables between the distribution panels and equipment. Cable tray comes in different materials (aluminum being common), widths, and configurations. Tray can be routed horizontally or vertically with offsets as needed.

Advantages: Light weight, can be routed fairly easily, size can be scaled up / down, tray cable can be routed from tray directly to equipment (with certain cable types), easy to re-route or add conductors as needs change, tray can be added if needed.

Disadvantages: Tray cable cost is higher than standard conductors, difficult to route in congested locations.

The choice of method will vary based on many factors. However, the most common factor I have found (unusually so) is simply owner preference. For open manufacturing floors I prefer cable tray for the advantages listed above. I prefer conduit for smaller or congested installations. I reserve bus duct for specific clients and needs. If making a selection for your project consult your engineer for a full evaluation of the different methods and the associated costs.

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