Check if your 12V or 24V DC cable run will deliver enough voltage to power cameras, access control or alarm devices reliably.
It depends on the cable size and camera current draw. For a 500 mA camera on 0.75 mm² cable, the maximum run is about 30 m before voltage drop exceeds 2 V. Use 1.5 mm² cable for runs up to 60 m. Always check the minimum operating voltage in the camera spec sheet.
24V DC systems have significantly less voltage drop for the same cable and load, because drop (V) = current × resistance, and 24V devices draw half the current of equivalent 12V devices (for the same wattage). Switching to 24V effectively doubles your maximum cable run length.
For a 100m run at 500 mA on 12V: 1.5 mm² cable has 24 Ω/km, giving a total resistance of 0.24 × 0.1 × 2 = 4.8 Ω and a drop of 2.4 V — too high. Use 2.5 mm² cable (14.5 Ω/km) for a 1.45 V drop, leaving 10.55 V at the device. Alternatively, use a 24V PSU and step down at the camera.