Video Cameras and AC Power

[Jerry Doran]

I'm very unclear as to the correct methods for powering video cameras safely. For example, why do video engineers/VTR ops insist that all cameras/monitors be on the same circuit? Is is true that camera BNC cables should be disconnected on a dolly when the dolly receives a bump? I know I'm not wording this very well, but I'm just looking for a brief explanation as to possible pitfalls or risks that can arise when power is not correctly set up.

[Walter Graff]

Generally it's refereed to finding 'clean' power. In building computers are often put on what is called 'an isolated ground' circuit. This means a circuit that has it's own dedicated ground different than the rest of the electrical boxes grounding. In general one wants to keep electronics together and separate from say lights. The reasons are that different pieces of equipment can create 'noise' on electrical lines that can interfere with cameras. For instance, the transformer from a light or a dimmer board may cause noise that can create hum in a video signal. And when you have multiple cameras you have all sorts of loopings of the ground via the AC and the video cables and clean curcuits can help you isolate any potential problems that may occur. So engineers start out by looking to keep all the cameras together electriacally so he has less potential interference fomr other pieces of equipment.

 

In the old days we used to use humbuckers in situations where noise was introduced to video cameras. It was basically a box filled with wax that had two BNCs and reduced the hum signal in video, while also degrading hte high frequencies slighly.