mains cables inducing LV cables

[tuckerkop81]

Guys, need some advice.

When measuring across some cctv cables, im getting around 0.80 v of AC, which in turn is causing mass problems with the system.

I have seen in our basement that the lv cables are run less than 2 inches away from the mains cables, so im sure the magnetic field is inducing the lv cables.

question being would a rubber mat between the 2 cables stop the magnetic field or is there another solution???

The run is around 20m in length

Any help would be greatly appreciated

Tom

 

[telectrix]

re-route the CCTV cables away from the LV ( mains ) cables.

 

[DPG]

Can't see how a rubber mat would stop induction. Also, 2" sounds a fair gap between the two I would have thought. The 0.8V could be normal - is it composite video we're talking on the cctv cables? Daz

 

[telectrix]

also bear in mind that a digital meter will show this sort of voltage with nothing there, if you are within 5 miles of 230V.

 

[tuckerkop81]

Thanks for your input guys. Our sub - contractors who i wont name have quoted a hell of a lot of money to sort the problem with the cctv. We feel theyre trying to pull a fast one.

Be nice to get to the bottom of it without this cost.

Thanks again.

 

[benji]

try an anologue meter

 

[Marvo]

If there's at least an inch separation distance along a 20m run I doubt it's induced voltages causing your problems. Is the video cable a shielded type? Is the shield connected either to a ground or a designated shield termination point? Can you give more info about the type of equipment and the type of cabling?

 

[PEG]

Good mention of the sensitivity of digital gear.This can be demonstrated to apprentices by showing an AC or DC voltage across a wet hair...

 

[Stroppy]

Works even better with your head jammed in a busbar chamber

On a serious note (and risking being shot out of the water), isn't the rule that you can have band 1 and 2 cables in the same trunking as long as they are seperated by a plastic wall? This would bring them a lot closer than the recommended 50mm seperation. I can't see what difference a 2mm strip of plastic (or a rubber mat) is going to make to an induced current, or am I missing something?

 

[DPG]

The rule about the plastic barrier between different band cables is for insulation, ie safety, not induced voltages. Daz

 

[Stroppy]

Ahhhhhh I see!