Saturday, May 15, 2021

How Not To Do A Grounding Bond.

Electricity is a weird thing that most people don't understand. They just flip on a light switch or plug in their phone charger and go about their day without really giving it another thought. In reality, it's a weird, almost magical thing that involves a web of science, theory and mathematical calculations. I've studied it, read books on it, and work with it daily and honestly I still don't understand it 100%.

But one thing I do (mostly) understand is "bonding". The ground in most electrical systems acts as a safety net of sorts and when there's more than one electrical system being used (like on a location where production may use the location's electrical outlets/"house power" while also bringing in their own generator) it's important to connect the two grounds so both systems are on the same "plane," so to speak. 

This is often done by attaching a grounding clamp to the grounding rod of the house we're shooting at (usually located below the electrical box of the location) and running the (appropriately sized) cable back to the generator and attaching the other end to the ground there. A good rigging crew knows this and is prepared to do this, seeing as how a Fire Marshall can shut the show down for the day if this isn't done. It's that important.

A bad rigging crew, however, will do this:




Note: out of all the ways you can safely run a grounding bond, taking the female Hubbell off a stinger, taping it to the grounding rod, and plugging the male end into the nearest distro box is not the proper way to do it, or at all acceptable, for many reasons. And to do all that without at the very least capping the live wires with wire nuts? ... I literally have no words. 




2 comments :

Anonymous said...

Genius!

Just hope the distro box in question doesn't get disconnected from generator - or you really may end up on multiple "planes".

Rule I'd heard was always go to the generator itself - as anytime you need a bond it'll be when the thing is running.

Just be glad no one was pumping water for a rain scene or anything like that.

Michael Taylor said...

I never felt comfortable working with different sources of electricity -- the invisible juice remains an unfathomable mystery. I posted this story on my blog years ago, but it seems worth repeating here. Back in the days before all our location cable was grounded, I BB'd a commercial filming at the Park Plaza hotel next to ... I think it's Lafayette Park, but could be McArther Park -- my memories of LA geography are fading up here in the woods. The genny was on the street next to a parking meter, and once all the lights were burning, I went back out to check the frequency -- there were no flicker-free HMIs back then. All was good, and I leaned with one hand against the parking meter while chatting with somebody, then reached down to pick up a coiled stinger that had been left on the fender of the genny. The instant the back of my hand brushed the metal fender, 240 volts of AC blasted from one hand to the other, right through my chest. It knocked me back a few steps and I saw stars, but I didn't go down. Once my wits were back, I measured the current from the fender to the parking meter -- it was 240, all right -- so I wrapped that meter in four inches of rubber mat and gaffers tape, then ran a grounding wire from the genny to a water pipe going into the earth near the Park Plaza. We had no further problems that day. Years later, during one of the Safety Passport classes on electricity, I asked the instructor what he thought might have happened that day. All he could say was "there must have been some potential between the meter and the genny, possibly from the Park Plaza or some other power source." None of that made sense to me then, and it still doesn't now. The lesson, I suppose, is be careful out there, kiddos...

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