Frequently Asked Questions
How do I size a UPS for a surveillance system?
Add up the wattage of everything the UPS must carry — the NVR or recording server, the PoE switch (use its full PoE budget plus switch overhead), and any monitors — then choose a UPS whose watt rating keeps that load at 60–80% of capacity. Runtime comes from the manufacturer's runtime chart at your actual load, not from the VA rating: a typical 1500VA/900W unit runs a 400W recording head end for roughly 10–15 minutes.
What is the difference between line-interactive and double-conversion UPS?
A line-interactive UPS corrects brownouts and voltage swells with an internal transformer and switches to battery in 2–4 milliseconds, which suits most recording head ends. A double-conversion (online) UPS rebuilds the AC waveform continuously with zero transfer time — specified for critical head ends, access-control servers, and sites with generator power or unstable utility feeds.
Do PoE cameras need their own UPS?
No — PoE cameras draw power from the switch, so putting the PoE switch on the UPS keeps the cameras running through an outage. The NVR or recording server must be on the same protected circuit; otherwise the cameras stay up but nothing records.
What is the difference between VA and watts on a UPS?
Watts measure the real power your equipment draws; volt-amperes (VA) measure apparent power. A UPS is limited by both ratings, so size against the watt rating — on commercial units it is typically 60–90% of the VA figure.