Sizing a power supply for a CCTV installation

An undersized power supply is one of the most common causes of cameras that reboot at night, and it is usually diagnosed as a faulty camera.

Add up the current, then add headroom

Each camera lists a current draw, typically somewhere between 300 mA and 1 A once infrared illumination kicks in at night. Total those figures and add at least 30 per cent. A supply running permanently at its rated maximum runs hot and fails early.

Infrared is why it fails after dark

A camera draws far more current with its IR LEDs on. A system that works perfectly all day and drops cameras at dusk is almost always short of power, not short of signal.

Voltage drops over distance

Thin cable over a long run loses voltage before it reaches the camera. A 12 V supply can arrive as 10 V at the far end, below what the camera needs. Thicker cable or a supply placed closer solves it.

Channels are convenience, not capacity

An eight-channel box does not mean eight cameras of any size. Check the total amperage on the label, not the number of terminals.