Experienced installer help needed - ground loop problem

[yamumsbum 0]

Hi, I have been sent out to a job which now I think is a bit over my head, I will out line the problem

 

- 16 channel dvr full with I think all samsung dome cameras, all on rg59 combined with fig 8 cable

- The site is made up of 2 steel framed structures, half of the cctv on one side, half on the other. Structure is about 10 metres away from one another. Furtherest run maybe 100m.

- 13 out of the 16 now have interference very similar to this - https://s5-us4.ixquick-proxy.com/do/spg/show_picture.pl?l=english_uk&cat=pics&c=pf&q=ground+loop+cctv&h=443&w=591&th=119&tw=160&fn=Ground-loop-interference-before-use.jpg&fs=85.1%20k&el=boss_pics_2&tu=http:%2F%2Fts4.mm.bing.net%2Fth%3Fid%3DH.5012957761177871%26pid%3D15.1%26H%3D119%26W%3D160&rl=NONE&u=http:%2F%2Fwww.doss.com.au%2Fgl001h-hi-performance-video-ground%2F&udata=ed7658c1e75fa5a0e96e05e5a4468760&rid=LALNPSOMKTLT&oiu=http:%2F%2Fwww.doss.com.au%2Fwordpress%2Fwp-content%2Fuploads%2F2010%2F10%2FGround-loop-interference-before-use.jpg

- Some of the interference is worse than others

- Battery test monitor shows them coming up fine (apart from 1 cam but i suspect the cam is actually playing up)

- They are all run off 4 power supplies, all powered from the same outlet as the DVR (I think all 12v, i think 2 different brands of psu)

- Customer advises 1 week ago it 'just started happening', DVR does not record far back enough to see the exact time, I can confirm with my own eyes that they were not like this in the past

- Was been installed approx 4 years ago

 

 

- I have tried every combination of unplugging psu's, individual cameras ect to try and see any change, which hasnt happened

- Tried a different DVR

- With a ground loop isolator the cams come pretty good, not perfect though, and not good enough for this customers expectations (although the cam that was not good on the battery test monitor did not change)

- I can see no pattern on the interference - For example I would have thought maybe all the far structure's cams may have been doing it, but there is 2 perfect looking cams screwed to the same bit of steel 10m away from the worst looking one?(surely with the same earth potential as one another) Also a couple of bad ones are maybe a 20 or 30metre run from the dvr? (surely with the same earth potential as the DVR)

 

 

- Now im not sure if i was on the right track, I measured at the DVR from each individual BNC (just floating in midair not contacting anything) to the DVR earth/ground. About half the cams were 0v AC, some 2.5v AC, and one measure 11v AC. Im not sure if this was even a correct way to testing for ground loops, but i thought the 11v AC was a strange reading, so i disconnected it from the DVR and PSU but no change happened. (what makes this even stranger is that the one that read 11v AC was a clear picture?)

 

I would have imagined a problem like this would have come up on the original installation, not 4 years later. The customer assures me no electricians/tradesman have been onsite. The way i see it is that if it all just started happening, there should be something simple to fix but i just cant see it, espicially if its taken 4 years to happen. One option is to buy 13 ground loop isolators, but im sure its not cost effective, and still the picture is not 100% clear as it used to be/still is on the test monitor.

 

 

Any suggestions?

Thanks

[jeromephone 6]

did you try running all the cameras off from one multi output psu also did someone check the ground on the outlet itself ? I would put a meter on the ground of the outlet and then contact the buidding frame or earth ground and see if you are getting any stray volltage