Power in a siamese cable

[garethnboyd 0]

Are there distance limitations when sending 12VDC along coax with a Siamese cable? Is the normal operating cable length for video in RG6 or RG59 the same for the integrated power?

[the toss 0]

The distance limitation for power is determined by a) the camera power requirements b) the cable used to carry the power c) the power supply. The type of coax doesn't come into it.

First of all look at the camera specs for working current & voltage range. This is what is required AT THE CAMERA for it to function correctly. The power cable will cause a voltage drop over its length determined by the cable length , the cable guage and the current. If you're not familiar with Ohn's Law then Google it , it is not difficult just basic maths.So , for

example if you have 100m of 24x020 cable supplying 300mA then the total voltage drop due to the cable would be- 100 x 0.025 (cable resistance) x 0.3 (current in amps) x 2 (supply & return leg). That would make it a 1.5V drop over the 100m. The camera working range would normally be able to accommodate this but not neccessarily. Many cameras run on 24Vac or are dual voltage ( 12Vdc/24Vac) By running on 24Vac you solve a few problems. Earth loops are seldom a problem because essentially the power is now a balanced feed. Voltage drop is less of an issue. The 24Vac cameras and the 12Vdc cameras are the same except that the 24Vac ones have an on-board power supply converting 24Vac to 12Vdc. This allows a far greater headroom before the cable induced voltage drop results in an unuseable voltage at the camera.

Hope this helps.