AC current is going nowhere near the water for fear of frying the talent. So what kind of options do I have to get this to be 100% safe?
You can use AC in and around water with 100% safety if you use GFCI devices – but I am not talking about only the hardware store variety (though you will want to use those too as part of a comprehensive ground fault system.) Large Amperage GFCI devices were, more or less, invented in 1996 for the production of the film "Titanic." Director Jim Cameron wanted the highest level of reality, which meant literally hundreds of people in, around, and under the water, with hundreds of submerged practical lighting units. On top of that there was assembled, what was to date, the largest lighting package ever used on a motion picture production consisting of 5,000 lighting units, requiring 50,000 amps of electrical power, and over 140 miles of distribution cable.
Because "Titanic" required a combination of HMIs, incandescent, dimmers and 'specialized' lighting units, "Titanic" Gaffer, John Buckley, and Rigging Gaffer, Mike Amorelli, realized that DC power would not accommodate all of the production's power needs. And, given the scale of "Titanic" traditional methods for handling AC around water (use of distilled water) was insufficient. Realizing "Titanic" required a new approach to working in and around water, they turned to Bill Masten and Rick Prey who operated a company called SMS Inc.
Primarily known for their award-winning NiteSun products - portable generator trucks with 120 ft booms for 12k HMIs - these two had already begun work on a protoype of a 208-240V multi-phase device which did not exist at the time. When Rick Prey worked on "The Abyss" in 1988 they used the electrical equipment that was available at the time, and as a Navy trained electrician, it scared him to death, Prey said, because, absent a Class A device, they "had protection, but not personnel protection."
After working with the Academy Award winning 100A Shock Block (developed by Stephen J. Kay of the K-Tec Corporation) on several more shows involving water (including "Crimson Tide"), Prey and Masten realized that high amperage multi-phase GFCI devices were technically feasible and were working on a prototype for such a device when approached regarding "Titanic."
Recognizing that the magnitude of power needed for "Titanic" (50'000 Amps in all) was beyond the scope of K-Tec's 100A Shock Blocks alone, Prey and Masten began work on developing ground fault protection devices capable of protecting circuits of 400 Amps, which did not exist at that time.
Familiar with the Bender Corporation's efforts on the "MagLev Train", a proposed high-speed rail line between Los Angeles and Las Vegas using a Magnetic Levitation Train, Prey and Masten thought that some of the same technology could be applied to their prototype and so they approached Marcel Tremblay at Bender with their schematics. With the help of Bender, SMS built a total of twenty-eight 1200 Amp GFCIs, and a number of 3-Phase 100- and 200 Amp models that were used, along with the 100 Amp 120-volt Shock Blocks from K-Tec, in the production of "Titanic." The proof of concept came when a high wind dragged a piece of heavy duty lighting equipment into the water, the 1200 Amp blocks SMS designed shut down power instantly - saving lives.
Using the "Titanic" production as field tests, Bender Corporation worked out further refinements to SMS's basic design for a 1200 Amp device until they had a unit that would meet the requirements for UL listing as a personnel protection device. Shock Block was subsequently acquired by the electrical manufacturing giant Littlefuse which introduced its' own UL listed high voltage multi-phase devices.
For more details on how to use GFCI to protect talent and crew in and around water see a curriculum that I developed on electrical hazard protection for the entertainment industry that is available at www.screenlightandgrip.com/html/481_GFCI_Workshop.html.
One important consideration in Ronnee’s case is the source of power. Ronnee, how had you planned to supply power to your dimmer packs?
Guy Holt, Gaffer, ScreenLight & Grip, Lighting and Grip sales and rentals in Boston
Edited by Guy Holt, 10 August 2013 - 05:31 AM.