RPPs are data center power distribution units that are field wired by electricians. The cables can run from RPPs to IT equipment either through the sub-floor plenum or overhead in cable trays. An electrician performs the wiring work onsite which includes: cutting, terminating, and connecting each branch circuit, and routing them to IT equipment racks.
The Advantages of RPPs
- RPPs offers a good amount of versatility in terms of building branch circuits to accommodate the specific needs of a server room.
- RPPs have the lowest initial cost of the three options, which is beneficial to companies with limited capital.
- RPPs can be adapted for both overhead configurations and subfloor configurations.
- RPPs can be placed more strategically to accommodate any problematic server room constraints.
The Disadvantages of RPPs
- RPPs require the most work to set up, as electricians must build the branch circuits instead of relying on factory manufactured products. This also increases the risk of human error as wire terminations may result in loose connections or other defects.
- If the cables are running beneath the subfloor, then they could obstruct cooling if the plenum is used to deliver chilled air to IT equipment.
- RPPs take up space on the server room floor.
2. Finger Safe RPPs
Finger Safe RPPs differ from traditional RPPs because there is no direct exposure to live bus while building a circuit. The bus is located safely behind a plastic resin-injected molding. Circuits are built using components that are manufactured in a factory. This reduces the labor and engineering associated with a traditional RPP.
The Advantages of Finger Safe RPPs
- Finger Safe RPPs use factory manufactured breaker components, which greatly reduces the risk of human error and reduces the labor to set up the data center power distribution unit.
- Finger Safe RPPs can accommodate changes in IT equipment faster than traditional RPPs.
- Finger Safe RPPs can greatly reduce the risk of arc flash when compared to traditional RPPs.
The Disadvantages of Finger Safe RPPs
- Finger Safe RPPs require vendor specific breakers that are unique to the specific manufacturer’s design. The customer may be susceptible to vendor supply chain shortages.
- Finger Safe RPPs cost more to change new power cables and breakers that need to be made for an equipment refresh.
Busway is a data center power distribution system where a power bus is generally installed over server racks and IT equipment. Plug in branch circuits or tap boxes are placed where they are needed along the bus. Cables run from the tap boxes directly to the IT equipment. Busway systems are generally installed with the maximum expected load accounted for before the installation.
The Advantages of Busway
- Busway has improved cable management and tracking compared to both types of RPPs because cables run directly overhead instead of running through cable trays.
- Busway eliminates extensive inventories of different cables because of the fixed distance between the IT equipment and the tap box.
- Tap boxes eliminate the need for extensive field labor associated with traditional RPPs.
- Busway accommodates an equipment refresh, adding on equipment, and moving equipment better than RPPs because of cables not being stacked on one another.
- Busway has a broad range of capacities available to address greater capacity needs.
- Time to install a new tap box and receptacle is much faster than circuit installation in an RPP.
Disadvantages of Busway
- Busway has higher initial costs in comparison to traditional RPPs.
- Row placement and length must be previously established, as the bus must be installed and cannot be easily moved.
- Busway requires a vendor to supply breaker/power cable assemblies.
- The busway capacity is ‘fixed’. Adding capacity to a rack row is disruptive to existing infrastructure systems (power distribution, lighting, conveyance).
RPPs, Finger Safe RPPs, and Busway
Benefits Compared Side by Side
The decision between these three options ultimately comes down to the needs of the individual data center. There are many reasons to use one over the other depending on the priorities of the data center.
Server rooms that utilize traditional RPPs may have lower initial costs as a priority. They also have floor space available for the RPP, but might have room constraints that do not facilitate a Busway system. Server rooms using traditional RPPs might do so if the final equipment layout is unknown because circuit branches can be built by electricians for the specific needs of the server room.
Server rooms that utilize Finger Safe RPPs usually do not have the lowest initial costs as a priority. They also would be more likely to have room constraints from using a busway and would need floor space for the Finger Safe RPP. Of the two RPP’s, Finger Safe RPP’s are better for data centers with mission-critical data, because they allow work to be done near live circuits with less of a risk of arc flash.
Server rooms that utilize Busway systems usually do not have low initial costs as a priority. Server rooms that use Busway systems are more likely to have constrained floor space, but plenty of space over the rows of IT equipment. They would also be more likely to use a Busway if there is a higher frequency of IT equipment turnover that would require new circuits to be installed.