Skip to main content


Showing posts with the label data-center

Watt and Volt-Amp (VA) Rating Notes

1. Definition and PurposeWatt is the real power drawn by the equipment.  The Watt rating to determine the actual power purchased from the utility company and the heat loading generated by the equipment.The VA rating is used for sizing wiring and circuit breakers.2. IT Equipment Switching Power Supply TypesPower Factor Corrected supply (PFC)Capacitor Input supply3. Computer Equipment Watt and VA RatingLarge computer equipment such as routers, switches, arrays, and servers made after 1996 use the PFC supply. Watt rating = VA ratingPCs, small hubs, PC accessories, and larger computer equipment made prior to 1996 typically use Capacitor Input supply. Watt rating = 0.55 ~ 0.75 * VA rating4. UPS Watt an VA RatingSmall UPS: Watt rating = 60% * VA rating (a de-facto standard in the industry)Larger UPS: Watt rating = VA rating5. ConclusionNeither the Watt nor the VA rating of a UPS may be exceededSizing the VA rating of a load to be no greater than 60% of the VA rating of the UPS ensures the W…