By the SightShield team · · 3 min read
Power cuts and dips are routine
Even in well-served areas of Bangalore, offices see power cuts, voltage dips and the switchover gap when a generator starts. Each one can reboot switches, corrupt a server or drop every phone call and camera at once. A correctly sized UPS keeps the network, servers, CCTV and phones running through short cuts and gives time for a clean shutdown or generator start during long ones.
VA, watts and load
UPS capacity is quoted in VA (volt-amperes) and watts. The watt rating is the real limit; for many modern UPS units it is around 80 to 100 percent of the VA figure. Add up the actual power draw of everything on the UPS — from equipment labels or, better, a power meter — and choose a UPS whose watt rating is comfortably above it, typically running at no more than 60 to 70 percent of capacity.
Example load for a 40-person office rack
A UPS with at least 1,000 W of real capacity, such as a 1.5 kVA online unit, keeps this rack at a healthy load level. Your own figures will differ, so measure.
| Equipment | Typical draw (W) |
|---|---|
| Firewall and two routers | 60 |
| Two 24-port PoE switches (with access points, phones, cameras) | 400 |
| NVR with 4 disks | 60 |
| Small server or NAS | 150 |
| Total | About 670 W |
Runtime and batteries
- Decide the runtime you need: enough to bridge to the generator, or enough for the whole cut if there is none.
- Runtime depends on battery capacity, not the UPS VA rating; external battery packs extend it.
- Lead-acid (VRLA) batteries are cheaper but last a few years and dislike heat.
- Lithium batteries cost more but last longer, weigh less and tolerate more cycles.
- Keep batteries cool — every few degrees of extra heat shortens battery life.
Online, line-interactive or inverter?
| Type | How it works | Use for |
|---|---|---|
| Online (double conversion) | Equipment always runs from the inverter; zero transfer time | Servers, network racks, sites with unstable power |
| Line-interactive | Corrects voltage; switches to battery in a few milliseconds | Small offices with stable power |
| Home inverter | Slower switchover, rougher output on some models | Lights and fans, not sensitive IT |
Shutdown and monitoring
- Connect the UPS to servers and NAS with shutdown software so they close safely before batteries run out.
- Use a network card or app to get alerts for power failure and battery faults.
- Label which circuits and devices are on the UPS.
Maintenance
- Test the UPS by switching off mains briefly every few months.
- Replace lead-acid batteries every three to four years, or sooner if runtime drops.
- Keep the UPS ventilated and dust-free.
- Do not plug heaters, kettles or printers into the UPS.
An example
An accounting firm in Jayanagar lost its file server twice in one monsoon when power dips rebooted everything. A 2 kVA online UPS with an external battery pack, shutdown software on the server and a network alert card now carries the rack for about 40 minutes — longer than most cuts — and shuts the server down cleanly if the power stays off.
Get your UPS sized
We measure your actual load and recommend and install UPS systems for racks, servers, CCTV and phones.
IT infrastructure services →Quick answers
How do I calculate UPS size?+
Add up the actual watts of all equipment and choose a UPS with a watt rating so the load is about 60–70% of capacity.
What is the difference between VA and watts?+
VA is apparent power; watts is real power. The watt rating is the true limit.
Can I use a home inverter for my network rack?+
It is not recommended for sensitive IT; online UPS units give clean power with no transfer gap.
How long do UPS batteries last?+
Lead-acid batteries often last three to four years; lithium lasts longer. Heat shortens both.
How do I get more runtime?+
Add external battery packs or reduce the load; the UPS VA rating alone does not set runtime.