Why Wear Shock Protection? This is Why

Rarely will you find me on a gig without gloves on my hands. I have a pair of Gig Gloves that I love to wear when I'm unloading trucks, a pair of buffalo skin gloves that I wear when I'm working around energized electrical cables, and a pair of voltage-rated rubber gloves that I wear when there is a possibility of electric shock (inside the restricted approach boundary for you who speak NFPA 70E). I'm always careful to meter power as far downstream in the power distribution system as I can because, the closer you are to the source of power, the greater the hazard. I cringe when I see people metering power at the camlock connectors on a portable power generator.

Recently, I was doing some research and I came across an OSHA accident report that said an employee touched live energized parts within a power generator.

"At 1:44 p.m. on August 30, 2018, an employee opened the 480 volt 3 phase diesel powered generator's output terminal panel and lifted the output terminal cover. The employee's hand touched energized parts and received a shock through his left hand between the thumb and the index finger, and was electrocuted."

This is why we wear shock protection. Had he been wearing rubber gloves, he would be happily working or relaxing at home with his family today. Even if he was wearing leather gloves, he would have fared much better. Instead, he's another statistic.

It's too late for this employee, but for the rest of us, we should learn from this. We can do better. Wear gloves!

Take Time to Save a Life

As of March 1, 2019, it's been 590 days since the last known fatal stage electrocution.

Barbara Weldens was a singer who liked to perform barefooted. On July 19, 2017, she was performing at the Léo Ferré festival in Gourdon, France when, according to Wikipedia, she stepped on "a faulty electrical device." It cost her life.

Could this have been prevented? What can we learn from the tragedy? How can we prevent similar tragedies in the future?

If the report is accurate, it would seem that the fault in the equipment was broken insulation on a power cable, leading to a live exposed conductor, which is a shock hazard. If she tread barefooted on a power cable with broken insulation, then she would have completed a circuit through her body to the chassis of the handheld microphone, which is connected to the shield of the microphone cable, and that is connected to electrical ground.

This illustrates the importance of visually inspecting all of your power cords and cables when you are setting them up. Had someone spotted the defective cable and removed it from service or repaired it on the spot, then Barbara Weldens would likely be alive today.

That's why I like to carry a roll of self-vulcanizing silicon rubber tape. When the backing on this tape is removed and it is wrapped, it forms a chemical seal and provides a layer of electrical insulation. Depending on the brand of tape, it can offer dielectric strength of thousands of volts per wrap. If I find any defective insulation, I will take the time to wrap it with self-vulcanizing silicon rubber tape. And because it's not very durable, I will cover it with electrical tape. The combination provides electrical insulation with a more durable outer covering. It's not a permanent solution but a temporary one that could save someone's life.

Defects in cable are common in live event production because of the way we handle them. We toss them around, step on them, run over them with hand trucks and fork lifts, and generally beat them up. They can end up with cuts, punctures, slices, abrasions, cracks, and other defects. Insulation is made of polymer, which is a form of plastic. As soon it's made, the insulation starts to break down naturally because of oxidation, moisture (leading to hydrolytic breakdown), heat (leading to thermal degradation), mechanical stress (leading to loss in tensile properties),  the effects of light (especially UV), chemical breakdown (due to atmospheric pollutants like oil residue on the surface of streets), biological breakdown (fungi, mold, etc.), ultrasonic breakdown, and more.

Self-vulcanizing silicon rubber tape is offered by a number of manufacturers under a variety of trade names including Rescue Tape, F4 Tape, Tape 70, and FixIt Tape. The price ranges from about $3.50 per roll (in packs of six) to about $18 per roll. You can find it at your local home improvement store or online.

Take the time to make sure your power distribution equipment is free from defects and you could save a life.

To Code or Not To Code?

Question: "I'm making some PowerCon and True1 jumpers, and I just realized that type S cable does not fit inside of the connectors. I know that, according to the National Electrical Code, we're not supposed to be using type SJ cable. What gives?"

PowerCon and True1 power connectors have become very popular in live event production, and many lighting fixtures now use one or the other. They work well, especially in touring applications where the gear is traveling to other parts of the world where the connectors are different. In the old days we would have to rewire the power cable with a new connector, and now we can simply change the entire cable without any tools. But you're right about these connectors not accepting the thicker type S cable, but they do work with type SJ.

Type S is what's known as "extra hard usage" cable. It's designed to be routed on the floor, and it can be stepped on, run over with a forklift, and generally abused and it will hold up well. Type SJ is "hard usage" cable, and it's not designed to be stepped on or run over by a forklift. It's supposed to be protected from that stuff.

It's true that the National Electrical Code says that, in theatres, audience areas of motion picture and television studios, performance areas, and similar locations, flexible cords and cables, including extensions, should be listed, extra hard usage cords and cables (i.e., type S). However, it also says that listed hard usage cords and cables (type SJ) are allowed for use as power cables on fixtures as long as they are not longer than 2 meters (6.6 feet), it mates to a listed, panel-mount connector on the fixture, it's protected by a circuit breaker or fuse not more than 20 amps, the fixture is a listed device, and the cord is "not subject to physical damage."

It also says you can use type SJ for Socapex breakouts as long as the longest cord in the breakout assembly is not longer than 6 meters (20 feet), they are attached to a pipe, truss, tower, scaffold, or some other structure to protect them from physical damage, and they are protected by fuses or circuit breakers not more than 20 amps. Lastly, type SJ cable can be used for two-fers as long as they are not over 2 meters (6.6 feet) long.

Of course, if you make your own adapters, they will not be listed, so they will not be code compliant. There are manufacturers who make and sell listed adapters, so now that you know the code, you can make an informed decision about what to do. Be safe!

Classic, Futuristic Lighting

If you thought you saw a Vari-Lite VL5 on the High End Systems booth at LDI 2018, you're not alone.

For the uninitiated, he VL5 was a classic moving yoke color wash fixture from the last millennium (1992, to be exact) and it had a most distinctive look. Instead of a lens on the face of the head, there was this radial tilting dichroic color mixing apparatus punctuated by a small metal cover in the center that made it look like a big pupil or a jet engine. It was the closest thing to Cadillac fins that the lighting industry ever had.

But you didn't see a VL5 at LDI, you saw the retro/futuristic TurboRay, the latest innovation from High End and Richard Belliveau. The fixture takes a fresh approach to a classic idea, updating it with a four-celled RGBW LED engine, gobos, variable frost, and a zoom lens. The effects it produces are unique, and the combination of the very narrow to super wide beam, the digital breakup, and the ability to create a four-color beam emanating from the head create a looks you've never seen. But the real eye-catcher are the tilting radial dichroics. They have been updated with optical edging to creates a sort of light-pipe that enhances the trapezoidal shapes and adds color to the edges of the filters.

I'm looking forward to seeing what Roy Bennett or some other very creative LD will do with them. My guess is that he would put them on a show by the dozens but the emphasis just might be the lights themselves rather than the beams they throw. But we'll have to wait until the Spring to see any of them on any show because they aren't shipping yet. Word is that they will start shipping sometime in the first half of 2019. In the meanwhile, I hope to see you at NAMM in January.

Zzzz....

Did you get enough sleep last night? If you work in live event production, the chances are you did not. Between our busy production schedules and the culture of "the show must go on," too often we are an industry of sleep-deprived individuals doing the best we can to make it to the next day off and hoping to catch up on our much-needed beauty rest.

It's a problem that was a major topic of discussion at the Event Safety Alliance's Safety Summit, which was recently held at Rock Lititz. The problem is that chronic sleep deprivation can lead to serious health problems, reduced cognition, temper tantrums, and, as a result, increased risk of accidents. There's a great Ted Talks video by Claudia Aguirre called "What would happen if you didn't sleep?"

Interestingly enough, in another Ted Talk by Jessica Gamble called "Our natural sleep cycle is nothing like what we do now," she talks about what has been learned from sleep studies. It turns out that when people are allowed to listen to their own body clocks and live without natural light (which allows them to sleep without even knowing what time it is), they tend to sleep from 8PM to midnight, wake for a couple of hours, and then sleep again from about 2AM to sunrise. Does that cycle sound familiar? If you've ever done a concert tour, you might have been lucky enough to catch some shut-eye during the show, typically 8PM to around midnight, load out, then go back to sleep again from 2AM until breakfast. Lucky you.

For the rest of us, it's time we seek solutions to this pervasive problem. There are no easy answers, but solving hard problems is what the live event production industry specializes in.

Event Safety Summit 2018 - Sleep deprivation and its consequences was a major topic of discussion.

Line Loss: Easy as 1, 2, 3

Today, we had a power lab (hands-on workshop) at Dadco Power and Light in Sun Valley, California. This is an annual event hosted by IATSE Local 728 for their members, and the owner of the company, Ron Dahlquist, generously provides space and gear. As part of the workshop, I wanted to demonstrate voltage drop (a.k.a. line loss). What is voltage drop? I'm glad you asked.

Every time you connect a load and turn it on, the supply voltage is applied to the circuit, but some of the voltage is dropped across the wiring, and what's left is applied to the load. The amount of voltage that is dropped across the conductors depends on the amount of current flowing through them and the resistance of the conductors. If the current is too high, or if the conductors are too small or too long, then too much voltage will be dropped and not enough applied to the load. How do you figure out ahead of time if that's the case? You're awfully curious, and I like that.

According to Ohm's law, the voltage that is dropped across the conductors is the current times the resistance of the wire. In the back of the National Electrical Code (NFPA 70), there is a table that gives you the resistance of copper wire based on the length and the gauge. I like to use that to predict voltage drop (sometimes called line loss).

At the workshop we had a setup with a 12kW tungsten lamp connected with 200' of banded feeder cable (#2 AWG). According to Chapter 9, Table 9, the resistance of 1000' of #2 AWG copper wire is 0.19 ohms. Since we had a 200' run, that means we had 400' of copper (200' to the load and 200' back to the supply). And since 400' divided by 1000' is 0.4, we calculated a total resistance of 0.076 ohms (0.19 × 0.4 = 0.076). Since the light operates at 120V, we also calculated a current of about 100 amps (12,000 ÷ 120 = 100). Therefore, we expected to measure a voltage drop of 7.6 volts.

After firing up the genny, we measured the current at the generator and it was 125 volts. Then we measured the current at the load, and it was 118.6. That means we had a voltage drop of 6.4 volts.

Our calculation was pretty close, but we weren't as close as Ron's estimate. Just before we measured the voltage drop, Ron whispered in my ear. "I'll bet the voltage drop is 6 volts," he said. He was closer than we were. How did he know?

Ron later told me that he has a rule of thumb that comes from years of experience. He calls it the 1-2-3 rule. It says that you will get about 1 volt of line loss per 100' of 4/0 AWG cable with 100 amps, 2 volts of line loss per 100' of 2/0 AWG cable with 100 amps, or 3 volts of line loss per 100' of #2 AWG with 100 amps.

The Roman historian Tacitus said, "Experience teaches." Yes, it does, but there is no better combination than experience and training.

Where does the electricity go?

One of the joys of teaching classes and workshops is watching the expressions on people's faces when they suddenly get it. That happened the other day when one of the attendees in a class pulled me aside during a break.

"I've always wondered," he said. "where the electricity goes. I thought it came back through the neutral and went into the ground."

He was pointing to an illustration I had drawn of a typical circuit, and he indicated that he thought the current literally flowed into the earth where it just magically...disappeared maybe?

Of course, that's not what happens at all. The current flows in a loop starting from the supply, then through the circuit, and back to the supply again. There is just enough energy to return the current to the supply, and then it starts over again.

The reason we earth our electrical systems by driving a ground rod (or using one of many other ways to connect the electrical system to the earth) is mainly for lightning protection and for a 0-volt reference, which stabilizes our voltage. If lightning strikes the building or the electrical system, the connection to the earth funnels the energy into the earth so it can be dissipated. But that connection has nothing to do with the normal path for current flow.