Solved: Horizontal Lines Interference In Video

On several of our cameras a horizontal line appeared after we rerouted wiring and installed a static switch in our access control room's intrusion panel. I suspect it is interference from the power cable running along side the siamese cables in the wiring gutter overhead. The power cable runs approximately 10 feet inside the gutter containing video and access control cabling. Is the 10 ft distance enough to cause this type of interference? Can shielding be added to the existing power cord or is this even the likely cause? If so are there any suggested methods for adding shielding? The interference began the second the static switch was connected. The cameras affected are 6 of a 16 channel encoder, and we have switched a single camera to an unaffected encoder with no change. The horizontal line appears in the same position of displayed video for all of the affected cameras.


On several of our cameras a horizontal line appeared after we rerouted wiring and installed a static switch in our access control room's intrusion panel.

1. Were the cables reterminated or replaced during the reroute?

2. Are the siamese power cables carrying AC or DC?

3. Did you change power supplies during this time?

4. How were the cables grounded before vs now, if at all?

Thanks for your quick response. No cables were reterminated or replaced other than the power source for the intrusion panel. The siamese cables are running DC power from DVTel EV216 encoders if I am not mistaken, and they are grounded at the encoders. The only power that changed was to add the static switch to provide power redundancy to the intrusion panel. The gutter is quite crowded though. We plan on pulling the intrusion system power tomorrow to see if the interference/lines go away in an effort to positively identify those power cables as the culprit.

What I would try:

Unplug any ethernet cables from the new static switch, (if any are connected), if the h line goes away, its likely a ground loop problem.

If it doesn't, can you lift the static switch power a few feet out of the gutter temporarily and see if that changes anything?

If that doesn't, it could be dirty power being fedback from the switch ps into the main, does the switch have an external supply that you can swap or reposition?

We plan on pulling the intrusion system power tomorrow to see if the interference/lines go away in an effort to positively identify those power cables as the culprit.

This is a solid step and likely the easiest test.

I don't think this is a shielding issue, but the test above will be the 'smoking gun' if it is...

Can you take a picture or video. Some systems that use an "Up The Coax" control signal can send a thin black bar up in the signal. It slowly travels up the screen, and is usually 1 pixel tall, and most of the screen wide - scrolls.... In this case, you would need to turn the coax control signal off on your control equipment.

Thanks everyone for your input. We pulled the power and the lines went away. When we connected to a second static switch they reappeared. Based on these findings the interference was isolated to the power cord's proximity to the siamese cable. We have scheduled conduit installation to eliminate the problem.

That's good that you've identified it.

I probably misunderstood what you meant when you were describing the scenario. When you say 'pulled the power', I am assuming you mean cut the AC power to the intrusion system at some upstream location, is that right? Not meaning physically pulled the power cable away from the siamese.

If that's true I'm not sure why there couldn't be a ground loop problem that started when you added a 'static' switch running on intrusion grounded power, that might also be connected cat 5 to the encoders of the cameras running on different power.

Just thinking out loud.