The power scheme drives cabling cost, installation effort and long-term maintenance, so decide it from the distribution of camera positions.

• Why PoE: one cable carries data and power, so no separate mains run is needed per position. Installation is faster, there are fewer failure points, and it is the best answer for scattered cameras.
• PoE limits: cable length and voltage drop cap a single run at about 90 metres. Switch power budget must be calculated, and high-draw PTZs or heated units require PoE+ or PoE++.
• Why separate supplies: power is not constrained by the switch budget, which suits large PTZ heads, heaters and strong illuminators. A single failure does not take out other positions.
• The cost of separate supplies: individual mains runs, plus outdoor waterproofing and surge protection, add noticeably to labour and materials.

Practical approach: use PoE for bullets and domes, and separate supplies for PTZs, heaters and high-power illumination, all managed from a distribution board for easier control and servicing.