Modern security cameras may use various power sources:

• 220 V AC (in the U.S., typically 110–120 V AC, but 220–240 V systems do exist in certain facilities)
• 48 V AC (rare in typical U.S. systems, more of a legacy or specialized scenario)
• 24 V DC
• 12 V DC

Uninterruptible vs. Non-UPS Supplies

Uninterruptible Power Supplies (UPS):

• Provide stable DC output (commonly 12 V or 24 V).
• Include an internal battery that continues to power cameras if mains voltage fails.
• Often come in wall-mount or desktop enclosures, sized for a range of total load current.

Standard (Non-UPS) Supplies:

• Typically provide a regulated DC output.
• When mains power is lost, the cameras fail unless separate battery backup is provided.

Centralized vs. Local Power

• Local Power: Each camera might have a small plug-in adapter (wall wart), typically 12 V DC, near the camera location.
• Centralized Power: A single higher-capacity power supply in a control room, from which cables run to each camera.

When using a single centralized power source:

• Each camera typically gets a separate pair of wires from the supply.
• The supply capacity should exceed the total camera load by at least ~30% to handle startup surges and overhead.
• Never use the coax shield as the power return.
• Conductor gauge must be adequate to keep voltage drop within camera operating limits, especially in cooler climates where wire resistance might increase.
• Observe proper grounding: if the power supply has a metal chassis, connect the grounding (PE) conductor to the enclosure.

Power Over Ethernet (PoE)

For IP cameras, PoE often simplifies installation:

• IEEE 802.3af (up to ~15.4 W per port)
• IEEE 802.3at / PoE+ (up to ~30 W)
• Higher-power variants (up to ~60 W)

In the USA, it’s increasingly common for network switches to include PoE on each port to power cameras via the same Cat 5e/Cat 6 cable carrying data. If a camera or switch port is non-PoE, you can add:

• PoE Injector: Inserts DC power onto the Ethernet cable.
• PoE Splitter: Splits out DC power from the Ethernet cable near the camera, feeding the camera’s power input if it lacks an internal PoE module.

Mode B (spare pairs used for power) was common in 10/100 Ethernet. Mode A (using center-tap transformers on data pairs) is often used for Gigabit or higher speeds where all four pairs carry data.

Determining Power Supply Size (Wattage/Amperage)

Each camera may have multiple subsystems drawing variable current:

• Camera electronics
• Auto-iris or motorized zoom lens
• IR illuminator
• Heater/fan (in cold-weather housings)
• Glass/window demister

Manufacturers often specify only a single power figure (e.g., “9 W typical, 28 W with heater and IR”). For safe design, use the maximum possible consumption for each camera, add them up, then apply a margin:

The factor “1.41” accounts for possible inefficiencies, surges, and a safety margin. If you have 4 cameras with maximum draws of 28 W, 7.7 W, 8 W, and 8 W:

1.41×(28+7.7+8+8)≈72.9 W1.41 \times (28 + 7.7 + 8 + 8) \approx 72.9\ \text{W}1.41×(28+7.7+8+8)≈72.9 W

Find a power supply rated slightly above 72.9 W (e.g., an 80 W or 90 W supply). If the supply rating is in amps (A) at 12 V:

Thus, a 12 V DC, 6.1 A or higher supply is required. The nearest standard size might be 12 V / 7 A or 12 V / 8 A.

Wire Gauge and Voltage Drop

Use a chart or nomograph to determine voltage drop along the DC power cable. Compare the delivered voltage at the camera end with the camera’s minimum operating voltage. If it’s too low, either increase conductor gauge (lower resistance) or use a higher initial voltage and step down near the camera.

Example: At 12 V and some known distance/amperage, if the camera only receives 10.5 V but needs at least 11.0 V, you must upgrade to thicker cable or supply 24 V (if the camera supports it) with a step-down converter near the camera.

Selecting Circuit Breakers (CB) and GFCI/RCD

A typical breaker and GFCI arrangement for a CCTV system might involve:

• Circuit Breaker (rated for the total load of DVR/NVR, monitors, and camera PSU).
• Ground-Fault Circuit Interrupter (GFCI) or Residual-Current Device (RCD) to protect personnel if a ground fault occurs.
• PE (Protective Earth), N (Neutral), and L (Live) conductors clearly labeled.

The rating of the breaker depends on total current draw, wire gauge, and local electric code. A typical small CCTV circuit might use a 10 A or 15 A breaker at 120 V AC in the USA, but always follow the National Electrical Code (NEC) and local regulations for exact sizing.