Camera lv power supply's all on same phase ?

I have to install a bunch of camera in a large warehouse. Powered by 12V power supplies, they are all going back to a dvr.
Someone told me that all the power supplies and dvr have to be on the same phase.
Is he right ?
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Sonbo wrote:

my recommendation: use what ever power source is convenient.
are these "wall wart" type supplies? are they grounded or do they just have 2 pin?
is the video output balanced or unbalanced?
i would just go ahead and install the system and should issues arise add buffers or isolators as needed. this will be MUCH less costly then bringing in electricians to rewire a building.
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A concern but probably less important that they be on same phase of electrical panel, you can have a situation where AC ripple, if out of phase between the camera , monitor or DVR will cause the vertical to roll. If this happens, reverse the AC side of the transformer/power supply and all should be ok. For example: if you find that some cameras roll and others do not, reverse the AC on the offending cameras.
Sonbo wrote:

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"
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Sonbo wrote:

If they are DC 12 volt, plug-in power supplies, it can't make any differencw because the output is totally isolated from the ac supply. I'm not sure about things if it's an ac power supply, directly to the camera. I've installed lots of them in warehouses and have not had a problem. I suppose that its possible that the NTSC signal from the camera, is phase locked with the ac line, and if they are out of phase you could have a brief picture roll issue, as you switch from one camera, to another, as the monitor locks in with the 180 out of phase signal. Maybe try the manufacturer, if possible.
Magna7878
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Sonbo wrote:

Are these security cameras? If yes, don't worry about it. They probbaly run on 12 volt DC, and this is a non-issue. You may have ground loop issues on the signal lines, which are easily solved by putting isolation transformers on the video signal lines. For higher grade cameras, then your video contractor has people who know exactly what they need, and which phase is not an issue. Power quality and good grounding practices are.
--Dale
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