HomeTechOps

Cameras

PoE budget calculator

Check whether one switch can power all your cameras using delivered watts and the 80% loading rule.

Use this before buying a PoE switch to confirm its total power budget covers your cameras' real draw — including PTZ/IR/heater spikes and cable loss — with safe headroom.

Low priority

Within budget — about 6 W headroom

6 cameras draw ~46 W (with 10% cable loss). Loading a 65 W switch to a safe 80% gives ~52 W usable, so this setup is within budget.

Total camera draw
46 W

incl. 10% cable loss

Usable switch budget
52 W

80% of the switch's total PoE budget

Headroom
6 W
Verdict
Within budget

First checks

  • Standard cameras: 6 × 7 W. High-draw (PTZ/IR/heater): 0 × 15 W.
  • Switch total PoE budget entered: 65 W (use the figure from the switch datasheet, not port count × class).
  • Enter each camera's rated max PoE power from its datasheet — IR and heaters change draw a lot.

Step-by-step troubleshooting

  1. 1

    Get the real per-camera wattage

    Read each camera's rated max PoE power from its datasheet (note PoE class).

    Expected: Accurate per-camera draw, including IR/heater modes.

    Next: Enter standard vs high-draw counts and watts above, then re-run.

  2. 2

    Size on delivered power and 80% loading

    Compare total draw to 80% of the switch's total PoE budget.

    Expected: Usable budget exceeds total draw with headroom.

    Next: If not, split across switches/injectors or pick a bigger budget.

What your answers suggest

  • Total draw = (std + high-draw) × watts × (1 + cable loss) = 46 W.
  • Usable budget = switch budget × 0.8 = 52 W.

Likely cause area

  • The switch's TOTAL PoE budget is the binding limit, not the per-port class — a switch can have many 30 W ports but a small total budget.
  • Size on delivered power (PD), not the source rating: 802.3af delivers ~12.95 W, 802.3at ~25.5 W, 802.3bt Type 3/4 ~51/71 W.

Safe actions

  • You're within the 80% loading guideline — leave the headroom for cold-start inrush and future cameras.
  • Verify long cable runs separately; voltage drop near 100 m reduces delivered power.

When to stop

  • Don't load a PoE switch past ~80% of its total budget — inrush and IR/heater spikes need headroom.

Assumptions

  • Per-camera wattage varies by model and IR/heater state — these are your entered values, not a per-model database.
  • Cable loss is approximated by the derate %; actual loss depends on run length and cable gauge.
  • PoE delivered power is always below the port's source rating.

What should I check first?

  • Get each camera's rated max PoE power from its datasheet (note the PoE class).
  • Find the switch's TOTAL PoE budget in watts — not just the per-port class.
  • Separate standard fixed cameras from high-draw PTZ/IR/heated cameras.

What is likely wrong?

  • Assuming port count × class is the limit — the switch's total budget is the real ceiling.
  • Sizing on the source rating (15.4W/30W) instead of delivered power (~12.95W/25.5W).
  • Loading the switch to 100% with no headroom for cold-start inrush.

What is safe to try?

  • Keep total draw under ~80% of the switch's PoE budget.
  • Move PTZ/heated cameras to a higher-class port or a second switch/injector.
  • Account for long cable runs — delivered power drops near 100m.

When should I stop?

  • Stop before relying on a switch loaded past 80% — IR/heater spikes can trip the budget and drop cameras.
  • Stop before guessing wattage; use the camera datasheet, since IR and heaters change draw a lot.

Source-backed checks

HomeTechOps turns official docs and conservative safety rules into a shorter runbook. These links are the source trail for the page direction.

Frigate docs: Recommended hardwareUsed for detector inference times, the cameras ≈ (1000 ÷ inference_ms) ÷ detect_fps capacity model, and the current 'Coral no longer recommended for new installs' guidance.Frigate docs: Camera setup (detect vs record streams)Used for the detect-on-substream / record-on-main pattern that drives bandwidth and detector load.FS.com: Understanding PoE standards and wattageUsed for the 802.3af/at/bt source-vs-delivered power figures and the switch total-PoE-budget constraint.