The densest, most power packed UPS available - offering HP customers more watts per U than any other UPS - allowing for more valuable rack space to be utilized by all your server, storage and networking equipment. The leading edge HP UPS R5500 Uninterruptible Power System features a slim 3U rack-mount design, offering up to 5400 Watts of true power. This new rack-space saving design allows more support for critical rack mountable equipment. This product brings unprecedented power density and innovative features to the proven HP family of rack-mountable UPS products. The UPS R5500 is a high power density solution, designed for customers who want to provide power protection in space-constrained rack enterprise environments. In addition, this new UPS R5500 has the capability to be connected to an optional Extended Runtime Module (ERM). Customers can further increase the run-time on their UPS R5500 by using this ERM. The HP UPS " models denote "Extended Runtime Capable" UPS models.