How do I choose the right rack-mounted UPS for my server room?

A rack-mounted UPS fits in a standard 19 inch rack and protects servers, switches and storage from outages and power problems. Use these steps to choose one.

1. Calculate your load

Add up the maximum watts of every device that will plug into the UPS. Add 20 to 30 percent for growth. Use the UPS's watt rating, not only its VA rating. Example: 2,000 W of gear plus 25 percent growth means a UPS rated for at least 2,500 W.

2. Choose the design

• Line-interactive: lower cost, adjusts voltage swings, suits small server rooms and network closets.
• Online double conversion: constant clean power with no transfer time, suits critical servers and storage.

3. Check the rack space

Rack UPS units commonly come in 1U, 2U, 3U and larger sizes. Larger capacity usually means more height and more weight. Check the depth of your rack and the weight the rails can hold, and put heavy UPS units at the bottom.

4. Calculate runtime

Decide how long you need. Five to fifteen minutes is enough for a clean shutdown. If you need an hour or more, add extended battery modules or plan a generator. Use the manufacturer's runtime chart for your load.

5. Match plugs and outlets

Check the input plug and the outlet types (C13 and C19) against your servers and power cords. Higher capacity models often need a 20 A or 30 A circuit, which an electrician may have to install.

6. Plan for monitoring

A network management card lets you watch the UPS remotely and shut servers down safely when the battery runs low.

7. Consider battery type and service

Lithium-ion batteries last longer than sealed lead-acid but cost more up front. Look for hot-swappable batteries, a maintenance bypass, and a warranty that includes the battery.

For high-availability rooms, use two UPS units in an N+1 setup so one can fail without dropping the load.