Security, Power & Structured Cabling · 3 min read

Sizing a PoE budget so cameras do not brown out

By the ECA Networks technical desk · Last updated 21 September 2026

Port count tells you how many devices connect. The PoE budget tells you whether they stay powered when every camera draws at once.

Short answer

Add the maximum wattage of every powered device, add twenty percent headroom, then choose a switch whose total PoE budget exceeds that figure.

Use maximum draw

Read the maximum power figure for each camera or access point. Night illuminators, heaters and motor movement can increase consumption above the daytime figure.

Total every device at maximum draw
Add at least twenty percent headroom
Check the per port wattage limit
Confirm whether devices use 802.3af, 802.3at or 802.3bt

Plan for the cable run

Long copper runs and poor terminations add loss. Keep permanent links within 90 metres and use solid copper cable where power delivery matters.

Frequently asked questions

What's the difference between 802.3af, at and bt?+

802.3af delivers about 15W per port, 802.3at about 30W and 802.3bt up to 90W. The camera or radio's datasheet tells you which class it needs, and the switch must support that class on every port you use it on.

Can one switch's total PoE budget be lower than its per-port maximum times port count?+

Yes, and it usually is. Most switches cannot power every port at maximum simultaneously, which is exactly why the total budget figure matters more than the per-port number.

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Sizing a PoE budget so cameras do not brown out

Use maximum draw

Plan for the cable run

Frequently asked questions

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