PoE Cable: The Budget Is Watts and Degrees
Quick answer / TL;DR: Short answer: use at least Cat5e copper, and prefer 23 AWG Cat6 for higher power. Class 3 (802.3af) provides about 15.4 W at the source, Class 4 (at) about 30 W, and 802.3bt up to 60 or 90 W. Distances still stop at 100 m, and bundled cables carrying high power need derating for temperature.
One category, three axes: shielding, conductor and jacket create the SKU.Power over Ethernet delivers DC on the same pairs as data. The cable has to carry current without excessive loss or heat.
Both limits are calculable, which makes PoE cabling a specification exercise rather than a guess.
Power Classes
| Standard | Source power | Typical device |
|---|
| 802.3af | 15.4 W | Phone, camera |
| 802.3at | 30 W | Access point |
| 802.3bt Type 3 | 60 W | Pan-tilt camera |
| 802.3bt Type 4 | 90 W | Displays, small PCs |
The delivered power is lower than source power because loss occurs along the cable, and that loss appears as heat in the bundle.
Cable Rules
- Copper, not CCA
- 23 AWG preferred above 30 W
- Check bundle derating
- Keep to 100 m
- Use shielded where EMI is high
Bundled cable in a warm ceiling is the practical limit: several high-power runs together can exceed the jacket temperature rating.
Real-World Applications
Ceiling access points at 30 W run comfortably on Cat6. A corridor of 90 W displays needs bundle calculation and possibly 23 AWG throughout.
Standards and Verification
| Reference | Relevance |
|---|
| IEEE 802.3af/at/bt | PoE standards |
| TIA-568.2-D | Cabling |
| IEC 61156 | Cable construction |
Derating figures for a specific bundle are not provided in the knowledge base. Consult the cable datasheet.
References
- IEEE 802.3af, 802.3at and 802.3bt
- TIA-568.2-D, Balanced Twisted-Pair Cabling
- IEC 61156-5, Symmetrical pair/quad cables
Practical Notes
Measure voltage at the device, not the switch. The difference is your loss, and it is the number that matters.
Related reading: ethernet cable — blogs/news/ethernet-cable
Related reading: cat6 poe cable — blogs/news/cat6-poe-cable
Related reading: poe adapter buying — blogs/news/poe-adapter-buying
Frequently Asked Questions
Does PoE work on Cat5e?
Yes, up to the power class the cable can carry.
What is the distance limit?
100 m, unchanged.
Why does a camera reboot?
Voltage drop or insufficient class.
Does CCA work?
Not for high power.
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