WTF - strange problem


I have connected 8 CCTV cameras over the BNC connector to DVR recorder. Everything works OK and picture is fine but there is one thing that i dont understand.

I have tested this problem with different 12V power supply's but the result is the same.

-------------------------------------------------- Installation cable: FTP shielded Maximum length from camera to recorder: 10 meters Wires used: blue pair for power, brown for video Wires for sensors ( the same FTP cable ): orange and green pair


As you can see i have used 2 pairs for video and two for PIR sensors because camera is near sensor.

Problem: Ih i connect PLUS of ANY camera to ANY power supply ( 3 different ones ) the camera is working !

I dont need the negative / GND. The voltage between outer part of BNC and PLUS of power supply is 12V.


- we have tested all blue pair wires and none of them is in short circuit, nor there is any voltage on the wires. The recorder is on the metal carrier that is connected on the metal profile but DVR is on rubber stands so this can not be a problem.

I have tested one PSU with eight 12V outputs, one 12V / 5A switch, one

12V/1A switch. Every time the same situation.

----------------------------- I would understand if one pair makes this kind of problem but all of them, this is simply not possible.

Where could be a problem ?

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You described your hardware quite well, but I do not see where you described your problem at all.

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the camera must be grounded somehow and the -12V connection is also grounded somehow.

Somwhow means via some wire or metal connection that ultimatly goes to ground. The most likely path involving the ground prong on the 3 prong power plug.


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------------------------ I would agree with you. I will try to plug the dvr on some other outlet that is not connected with the one that am using. Then i will check all groundings and i hopefully i will find error...

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Use a UPS. Or an isolation transformer or a variac even.

Also, use an isolated AND adjustable (current and voltage) 12V supply at least to perform diagnostics with.

You may want isolated dongle type DC supplies for the actual job.

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On Monday, March 2, 2015 at 10:51:09 AM UTC-5, wrote: The most likely path involving the ground prong on the 3 prong power plug.

...or the BNC connector, if I understand his setup correctly. If so, then un-making the BNC connector should cause the camera to lose power, but you'll have to watch the power light indicator on the camera (if it has one), since you would obviously lose the video feed.

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One STILL has ground via mains to any supply. Also consider shielding of any wire pair as a ground line. If you could use an isolation transformer to one supply, you maybe able to narrow down that problem.

Reply to
Robert Baer

  • A variac DOES NOT give isolation.
Reply to
Robert Baer

That may be a way to find the problem, bu a "ground loop" could still be present via mains/power wiring.

Reply to
Robert Baer

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