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#1 Jerry Doran

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Posted 07 December 2007 - 02:15 PM

I've been on a bunch of video shoots lately and been surprised by the haphazard cabling and distribution of electricity to the cameras, monitors, etc. What are the best ways of dealing with this on set? Is it risky to have BNC cable running next to/over electric cables? Should electricity to cameras/monitors all come from the same source? What are the potential risks if things are cabled/powered improperly?

Edited by Jerry Doran, 07 December 2007 - 02:16 PM.

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#2 Michael Nash

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Posted 08 December 2007 - 03:12 AM

Most of the time it's not a problem because the signal that's going through the BNC cables on set is usually only used for monitoring, not recording. So if there is some RF interference it's of no real consequence; and if it is visible, well then, it's visible and you can do something about it. It's not like audio cabling where the signal is going from the mic through cables before it gets to the recorder.

As far as powering different components off the same circuit, again it's usually not a problem for the same reasons. In a studio or control room situation where the video signal may get passed through several devices before recording you probably want to ground in common and take other precautions, but again on set you're usually just monitoring with different devices.

Proper BNC cabling of an analogue signal is a different and more complex subject.
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#3 Phil Rhodes

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Posted 08 December 2007 - 05:39 AM

The only time I have problems is on location with an ungrounded generator. Generators are always supposed to be grounded, without exception, although I fully appreciate that this is not always practical and it's one of those things that people tend to get a handwave on. I've had fairly serious problems when mating BNCs run from mains-powered equipment to battery equipment, and I've seen visible sparks drawn between connector shells. One day that's going to kill a piece of video gear, and I wouldn't want to be the spark responsible.

It doesn't take much to solve the problem - the standard, unofficial technique of rolling the truck over an earth stake laid on the ground fixes the situation. People should at least try, especially when there's big, leaky devices like HMI ballasts around.

Phil
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#4 John Sprung

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Posted 12 December 2007 - 03:12 PM

Grounding a generator isn't just an interference issue, it's also a life safety issue. If nothing else, pound a couple feet of rebar into the dirt.




-- J.S.
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#5 Phil Rhodes

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Posted 12 December 2007 - 03:35 PM

My thoughts precisely. The excuse is often "that isn't to code, so why bother."

Translation: we can't be arsed.

Phil
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#6 Freya Black

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Posted 12 December 2007 - 04:50 PM

Proper BNC cabling of an analogue signal is a different and more complex subject.


Please tell me more!

Can I connect professional BNC outputs to domestic style phono sockets without running into weird problems? Do I have to keep the BNC output as far away as possible from the mains powered 12v inlet cable?

Anything else you can tell me?

love

Freya
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#7 Phil Rhodes

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Posted 12 December 2007 - 06:26 PM

> Can I connect professional BNC outputs to domestic style phono sockets without running into weird problems?

Not always, but usually. Phonos are crappy; they get loose, they fall out, etc. They're not impedance matched, which can cost you sharpness and even lead to strange multiple image and trailing effects, especially on long runs. The operative point with this is that the only things that composite video is really used for is basic-quality monitoring and video assist, where the image is so awful to begin with it's a moot point.

I've never had problems running video and power together - that's why video cable is screened. Obviously, if you start seeing problems, it's something to look at...

Phil
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Rig Wheels Passport

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Broadcast Solutions Inc

Ritter Battery

Gamma Ray Digital Inc

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Aerial Filmworks

rebotnix Technologies

Metropolis Post

CineTape

The Slider

CineLab

Glidecam