Power over Ethernet has grown well past the modest budgets of its early versions. IEEE 802.3bt, the standard often marketed as 90W PoE, raised the ceiling enough to run devices that used to need a separate power supply. For security installs, that changes what a single Cat cable can support at the edge.
Types and power levels
802.3bt defines two higher tiers on top of the earlier 802.3af and 802.3at. Type 3 delivers up to roughly 60W at the source port. Type 4 delivers up to roughly 90W at the source port. Because of resistive loss in the cable, the power available at the device is lower than the port figure, which is why power sourcing equipment and powered device ratings are stated separately. A key difference from earlier PoE is that 802.3bt uses all four pairs in the cable to carry power, where the older types could use two.
What it powers
The extra headroom matters for the loads that used to defeat PoE. Outdoor PTZ cameras draw heavily during pan, tilt, and zoom motor activity and during infrared illumination. Multi-sensor cameras, which pack several imagers into one housing, have a higher steady draw than a single fixed dome. Built in heaters and blowers, needed to keep domes clear in Canadian winters, add a significant load on top of the camera itself. Type 3 and Type 4 budgets make it realistic to run these devices over one cable rather than pulling local power to the pole or wall.
Cable and heat considerations
More power on the wire means more heat in the wire. When many powered cables share a conduit or a tightly packed bundle, the bundle heats up, and that raises resistance and lowers the power that reaches the far end. For higher power runs, prefer larger conductor cable, keep bundle sizes reasonable, and pay attention to the ambient temperature where the cable sits. Distance still matters too, since the standard assumes a maximum channel length and losses climb over long runs.
Match the powered device rating to a power sourcing equipment port and switch that actually supports the right type. A switch with a high total PoE figure can still starve devices if its per port budget or its overall power budget is exceeded once every port is loaded. Add up the worst case draw of every connected device, including heaters running in winter, and confirm the switch can supply that total at once.
Specified carefully, 802.3bt removes a lot of the local power runs that used to complicate camera placement. Specified loosely, it leads to ports that brown out on a cold night when every heater turns on together.