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class="style19"> Humbuckers

>Published : 23rd September 2008

>Hi everyone,

>I know we had a discussion about this recently (cml-lighting: Grounding to Fire Hydrant), but I'd like to add that your suggestions saved the day last night. My camera assistant was complaining that he was getting a shock when he was reloading our 435. I thought for a second that, since we were working in the rain, it might have been that the video playback kit might have been electrifying our camera.

>My first thought was to have the dolly grip plug in the dolly to neutralize us to earth, but I remembered Mark Weingartner's recent posts, and stopped the grip from plugging it in.

>I asked the electricians for a voltage sensor "sniffer", and sure enough holding it to the camera caused it to glow red and buzz. When the video playback was disconnected, the camera was no longer hot. This helped determine the source of the problem, and when they asked for a solution, I said we needed an isolation transformer for the video line. The guy looked at me and said, "Oh, you mean a humbucker? I got one right here". Problem solved, and probably saved us from doing big damage or hurting someone by plugging in the dolly.

>My question is, then, what causes this to happen? Is it a short circuit in the playback equipment? A bad cable? Were we lucky we didn't injure or kill someone?

>Can't thank you guys enough for a wealth of knowledge that proved very useful last night. I got to remember to get one of those suckers for my kit.

>All the best,

Graham Futerfas
Director of Photography
Los Angeles, CA
www.GFuterfas.com


>Absolutely, plus every time one of these little discharges occurs there is the real chance of a discharge spark exposing a bit of film. I had a nasty experience with a poorly designed aftermarket videotap on the door of an Arri 2c.

>There was a point when it would shock so often that it would bring a tear to your eye as you operated. I fixed it myself in the field but the real tears came when I discovered the "lightning bolts" across the images during dailies.

Producers can call us babies afraid of little shocks and such, but they'll change their tunes if the footage is ruined.

Also, as a note for the cold, dry winter, has anyone else experienced the issue of static electricity discharge on their cameras? I get this all the time from clothing rubbing as I move and darn if the tripod or camera isn't always the first thing I touch, giving a little spark. I worked with an old school guy way back who during the cold would stick a small damp sponge inside the camera as a discharge point for these sparks. He claimed it was easier than running a spike wire to the camera (a copper wire attached to some bare metal on the camera on one end and a nail shoved into the ground on the other, also affectionately known as a "bulldick"). Said it was great on Mitchell’s & Arri 2cs and important on black & white stock (like I said, old school). Don't know what he'd do on modern cameras with so little space inside.

Mitch "I'm really not that old, really." Gross
NYC DP/TD
Abel Cine Tech


>BTW\... I had same thing happen a couple years ago on a very rainy muddy shoot out at Ventura Farms, video village sending juice up to the camera. Cam Ops and Asst's wearing fleece and neoprene gloves to stay iso'd until Electrics simply clipped an alligator clamp to the camera that went back to Genny Ground, and problem disappeared.

>mdp


class="style20">"I guess you could say the trouble started back at Boulder Dam".

>Great story, and my new favourite punchline. Worthy of a t-shirt. Up there with Cimino's "Heaven's Gate" line which is one of my faves. I think I read it in Steven Bach's book about "Heaven's Gate". The story goes that when the 1st AD tried to call (or did call) for lunch just as a complex, back-lit exterior master setup with multiple
cameras, dozens of horses, complex costumes, wagons, tons of extras, dust (and more dust), that had taken all morning to block and rehearse was getting ready to roll the first take, Cimino reported snapped, "This is bigger than lunch!"

>"This is bigger than lunch" t-shirts appeared on the set the next day.

>Heaven's Gate ... an under-appreciated film for it's wonderful craft in all depts.

>Greg Lowry
Scopica Inc. / Scopica 3D
Vancouver


>I often get a very light electric shock from the (film)camera or dolly.
It happens everywhere, even in the studios and seems to come from the BNC.
I disappears when the BNC is disconnected.
All power is grounded.

>Why is this and what can be done to avoid it?

>Best regards

>Jens Jakob Thorsen DFF
Director of Photography
Denmark EU
+4540508840
www.jensjakob.com


class="style20">>>The thing to remember is that these transformers generally work only on composite analog video, >>and will not pass SDI or HDSDI at all. So they're only useful for isolating video taps and composite >>analog monitors

>In fact there are now SDI and HDSDI transformers available from Allen Avionics, but as far as I can tell, they are not isolation transformers, just humbuckers with no AC or DC isolation. B&H carries them:

>http://tinyurl.com/2om7tp

>Allen Avionics also makes a line of composite video isolation transformers in single and triple versions, and also a version for S-video:

>http://www.allenavionics.com/AVI_Trans/VIT.htm

>I have used the North Hills product line successfully for a long time:

>Information :

>http://www.northhills-sp.com/products-wideband-video-isolation.html

>A PDF file with model numbers :

>http://www.northhills-sp.com/pdf/products-wb-humstoppers.pdf

>A retailer :

>http://rdstuff.stores.yahoo.net/viistr.html

>Remember, you're looking for something with DC isolation that has a 75:75
impedance (75 ohms in, 75 ohms out).

>Disclaimer: Don't be shocked, but I have no financial or romantic interest in anything mentioned here.

>Bob Kertesz
BlueScreen LLC
Hollywood, California


class="style20">>> Do LCD monitors have the problem of voltage leak down the BNC
>>Most seam to use a low voltage external double insulated PSU

>I would have thought that they would use switching power supplies which may or may not be totally isolated from mains...

>I believe that the problems of ground loops and raised voltage of chassis of various components stems from the unfortunate design of some video equipment, (monitors, switchers, video cards in computers, recorders of various types, and, indeed motion picture cameras when they have video taps attached to them) where the signal ground (the shield conductor of a BNC or RCA coaxial cable) is electrically bonded to the chassis of the electronic device (or motion picture camera) Since multiple components are built this way but not all of them (and with some of them that signal ground potential is significantly above line (mains) ground (earth)) the outside case of some components, especially the one we have to stick our eyes and cheeks against can be energized - can have their voltage raised above ground.

>The first thing that many video assist and sound and camera people will do when this happens is to put a ground lifter (three pin -to-two pin adaptor) on their power strip so as to disconnect their power supplies from ground. This may get rid of the ground loop but does not necessarily provide a safe working environment... now the equipment case (or camera body) may be energized above ground... and if you end up touching something that IS properly grounded, like a light stand at the same time that you are touching your dolly or camera, you can get a nasty shock.

>Mark Weingartner
LA based VFX DP/Sueprvisor


Mark Weingartner writes :

>>>The first thing that many video assist and sound and camera people will do when this happens is >>to put a ground lifter...........This may get rid of the ground loop but does not necessarily provide a >>safe working environment...............

>When I've run into this practice, I ask the culprits if they're prepared to pay damages to any widows or orphans newly created if someone is electrocuted as a result of pulling ground pins or lifting grounds. In studio construction I have usually been able to create the single point ground system necessary to eliminate ground loops by working with the electricians (or architects) involved and having the powerline grounds laid out so that the equipment is single point grounded through the equipment powerline ground wires. This obviously isn't practical in the field or with setups but the fact remains that it is highly dangerous for electrical safety unknowledgeable people to play with grounding, particularly around something as potentially lethal as sets and locations, either indoor and outdoor.

>Hal Smith
Engineer and Somewhat DP
Edmond, OK


>It amazes me that video assist equipment suppliers and operators do not utilize a 1:1 isolation transformer between the mains power and their equipment, if for no other reason than for reducing liability.

>I too have been shocked by touching the camera on a damp set. Another time during a dolly shot, the camera dolly touched a light stand and the camera electronics went up in smoke. Luckily no one grabbed the lamp stand and the dolly at the same time.

>Bill Bennett, ASC
Cinematographer
Los Angeles, CA, USA


>In 1979 0r 80 we were doing the first ever American feature with the Louma Crane - the movie 1941. Video taps were rare, remote cranes - we were the only one. On this day the grip swinging the arm missed his mark by a little and touched a 10k up in the beds. There was a shower of sparks at the light and smoke started pouring out of the Louma operators console - you can imagine what followed. We pulled the covers, started changing fuses, power supplies, monitors, anything that wouldn't light up until about twenty panicked minutes later the crane came back to life. But it wasn't over. A court of inquiry was convened in "The Tent" Spielberg's command centre - Jean Marie Lavalou, Bill Fraker, Gary Dodd the key grip, Doug Pentek the gaffer and myself. Steven started with "Who is responsible for this?". There was a long minute of silence and then Doug Pentek quietly said "I guess you could say the trouble started back at Boulder Dam"....nobody else said a word - and after a while we went back to work.

>Andy Romanoff
EVP Technical Marketing and Strategy
Panavision - Woodland Hills


>Check to see if the earth is connected on the video power cable. It is common practice with some video guys to remove (lift) the earth to get a better picture (Sound department also do this for similar reasons) I have lost count of the number of times this has cropped up

>"Yes, I remember the days of getting bad shocks on the set but it simply doesn't happen these days."

>As for PAT testing being required in the UK you don't have to look to hard to see that it is not taken seriously by most rental companies

>In God we trust

>Robin S Brigham
Gaffer
London


>Hi Jens,

>What you experience is a electrical leak probably in the monitor that finds it's way by BNC to you. It is very, very annoying and I have had it many times as well. When I have these leaks nowadays I usually take a piece of electric wire of ten meters. Fix one end on the videocart or better on the groundplug of the monitor if it has one, fix the other end (with open copper of course) on the water piping or some other ground spot in the vicinity. That should do the trick. When I had this on a TV show some years ago, grounding of the videocart also reduced the numbers of hair in the gate a lot.
Good luck, there.

>Herman Verschuur
Amsterdam, Netherlands
1st AC, Shooter


>Hi Brian

>IPAT testing may be Mandatory but it is not actually done by everybody

>Most but not all lighting companies test "most" gear but on any set in any studio there is untested equipment -apart from lights and camera departments, Construction, wardrobe and makeup, special effects, catering and most video/sound playback departments simply don't do this and as for the Art dept/prop hire companies

>I as a gaffer supply all these people via RCDs on set but there gear no more has a PAT test than a MOT !

>Getting back to the Humbucker/isolation thing
Do LCD monitors have the problem of voltage leak down the BNC
Most seam to use a low voltage external double insulated PSU

>Robin Brigham
Gaffer
London