The short answer: an IP camera draws 5–8 W, a PoE switch adds 3–5 W overhead plus the camera load, and an NVR adds 20–40 W. For a four-camera site the switch, not the cameras, sets the runtime. A PE-DU18 class unit holds four cameras and the switch for 3–4 hours; eight hours needs a larger pack. Transfer is 10 ms or less, so recording does not stop.
One working day to a written answer · sample from one unit
Most outages do not take the camera down. They take the switch down — and every camera behind it goes dark at once, with nothing written to the NVR for the duration. Sizing for the cameras alone is the most common mistake we see in site surveys.
Two sites with the same camera count can need different products. What moves the specification is whether the cameras are PoE, whether recording must survive the outage or only the cameras, and how long the gap actually is.
PE-DU18-P puts the PoE injector inside the UPS, so a single camera and its injector run from one box with no separate switch. PE-DU18 covers a router, ONU or small switch on DC outputs. PE-DU18-C takes a 12–18 Vdc input where the cabinet already has a DC bus.
For larger sites we build AC-output units from 300 W to 10 kW with pure sine output, sized per camera count and required runtime. All units transfer in 10 ms or less, and CE, RoHS and UN38.3 documents are available for verification before you order.
Four IP cameras at 6 W each plus a PoE switch drawing about 8 W is roughly 32 W. A PE-DU18 class unit covers 3–4 hours at that load. Eight hours needs a larger pack, which we build to order rather than pretend a small unit can do.
Only if recording must survive the outage. If the cameras stay up but the NVR does not, you keep the live view and lose the evidence — which is usually the opposite of what a security spec wants. Put both on the backed-up circuit and add 20–40 W.
No. DC drops over distance, and a 12 V rail loses several percent per ten metres of thin cable. One unit per cabinet, sized for the cameras behind it, is cheaper than one large unit and thick copper.
It covers the camera, not the switch or the NVR, and the batteries are usually small. It is a reasonable belt-and-braces addition but not a substitute for backing the switch.
Camera count, adapter rating or cabinet bus voltage is enough to start. You get a model, a runtime figure and the document list for your market.