When I was a very young child, my mother used to ball up a piece of red thread, moisten it and stick on my forehead to cure my hiccups. Oddly enough, it worked every time. But it had to be red thread; blue, black, yellow, or green just wouldn’t do. Why? Because that’s the way it has always been done. Mom’s mother passed it down from her mother, who passed it down from 1,000 mothers before her. And if you went back far enough you would probably find that the red thread was specifically selected from a variety of different thread colors based on an extensive scientific study involving the world’s most brilliant scientific minds funded by some international alliance of wealthy nations. Or it could just be an old wives tale.
The truth is, there are lots of old tales and remedies, some of which are true and work, others of which are not and don’t, but all of which were passed down through generations and accepted as unquestionable truth. But in the realm of live event production, we have no such equivalent. Everything we do, every breath we take, every move we make, is firmly rooted in scientific fact…with the possible exception of one, maybe two things. Like that ghost light thing. You know what I’m talking about — the bare bulb on a stand that is left burning through the night year-round to scare away ghosts. It makes perfect sense to me. If kids are afraid of the dark, then surely ghosts are afraid of the light. Someday we’ll have scientific proof of that, but for now, it’s just what we do.
There are lots of other notions that have been handed down through time that may not necessarily be based in scientific fact. I received a phone call from someone who said that they had been warned repeatedly not to wrap cables around a batten because it would cause current to flow through the batten. Is that true, or is it fable?
A coil of wire or two and an iron core are the basic elements of a transformer, and a transformer does generate a current in the secondary coil. But there are some very important differences between a transformer and an iron pipe wrapped with a power cable.
First of all, in order for a coil of wire wrapped around a batten to generate a secondary current, there has to be a secondary winding. It’s not inconceivable that a second cable would be wrapped around the same batten, but that would not cause current to flow in the batten even if it did cause it to flow in the second coil of wire.
Secondly — and this is the most important distinction — in order for current to be generated in the secondary coil, there must be a magnetic field cutting through the secondary coil. Michael Faraday first learned this in 1831 when he was trying to figure out how to generate current with a magnetic field. He reasoned that if a current flowing through a wire produces a magnetic field around the wire — and it does — then a magnetic field should be able to produce a current in a wire. So he took an iron toroid and wound two coils of wire around it. On one of the coils he connected an amp meter and to the other he connected a battery. He thought that by having DC current flow through the primary coil that the magnetic field it generated would somehow transfer energy and cause current to flow through the secondary coil. But he was baffled when it didn’t work. He did, however, notice that when he first connected the battery to the primary coil that the amp meter glitched. That gave him a clue about what was going on. He thought about it deeply until he eventually figured it out. What he learned is that a static magnetic field would not generate current in the secondary winding but a changing magnetic field would. That’s why a transformer only works with alternating current and not direct current. As the current in the primary coil goes from positive to negative 60 times per second in North America, or 50 times per second in Europe and Australia, it creates a magnetic field that alternately grows and collapses. The magnetic lines of flux then cut through the conductors of the secondary winding and in the process it causes current to flow.
But the cable that we usually rig to a batten is most often a multiconductor cable where the return current in the neutral is balanced by the outgoing current in the branch circuits; therefore, the magnetic fields generated by the outgoing currents are equal in magnitude and opposite in direction, so they cancel each other. There is no secondary current even if there is a “secondary coil.” As they say on television, myth busted.
There may be very good and logical reasons not to wrap a cable around a batten. First of all, it takes longer to set up and second of all it takes longer to break down. And if you wrap one cable on top of another and you then have to replace a defective piece of gear, it will take you three times as long to unwrap the mess of cables.
A better way to rig a batten is to run all the cables and secure them to the pipe using black tie line. Tie them with a clove hitch and finish it with a bow. It’s quick and easy on the in and even quicker on the out, and we all know it’s all about the out.
Maybe a wise old stage hand conjured up the myth of the generated current in a batten wrapped with a power cable after he grew frustrated trying to keep his young hands from doing so. Whatever the reason, not wrapping cables is a good idea. By the same token, keeping a light burning on stage at night serves to keep wayward wanderers from falling into the orchestra pit or stepping off the lip of the stage. So don’t confuse me with the facts, my mind is made up.
