The distance the power can travel depends on the thickness (Gauge AWG) of the cable and the amount of power being drawn.
Typically a fixed lens 12 volt CCTV camera will draw less than 500ma of power and as a guide a Cat 5e cable is 24AWG and a Cat 6 cable is 23AWG. If your power cable is a multi-core like Cat 5e or alarm cable you can use more than one core to extend the distance.
The following tables provide approximate distances that can be used a a guide
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