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Electricity Electricity is one of the simplest things we work with, Just electrons flowing across a conductor alternating 60 times per second (50 Hz in Europe. However, due to the nature and importance of electricity we must show it the utmost respect. After all every piece of gear on stage, in a truss, at the mix position, and in the control booth must depend on it. We probably shouldn’t forget that it could kill you also. I will briefly discuss current (AC Vs. DC), Phase (single Vs. three), grounding, and Neutrals. AC vs. DC You have to go back to the turn of the twentieth century to get the full scoop on the Battle between the supporters of Direct Current and Alternating Current. Direct Current, which is exactly as its name implies always on always traveling in one direction (such as a battery, in which there is a direct flow from the negative to the positive terminal, was backed by Thomas Edison. Alternating Current, a form of electricity that changes polarity 60 times per second (it has a waveform, in which polarity reverses based on current frequency), was supported by a former employee of Edison, N. Tesla (the inventor of AC) and his new employer, Westinghouse. The problem with DC is that it can only be transmitted over a conductor for about a mile before it starts to lose power. However, AC, after being converted to high voltage, can travel for hundreds of miles (similar, in a way, to a 70 volt line in audio). AC won and is the power of choice for Transmission, but DC did not go the way of the buggy whip. DC is still used in batteries, internal circuit boards of advanced electronics, and in many industrial applications. Phase, Legs, and voltage Electricity as we know it while tying-in the touring company’s tails into the house disconnect or tightening the lugs to send electricity to permanently install a VX Dimmer rack, or just plug in our cell phone chargers, comes in two formats Single Phase and Three Phase. The term Phase is associated with the cycle of the AC power; this can be compared to phase in audio. In single phase you have two hot legs of AC power that are in phase with each other, or cycling identically. In Three Phase you have three hot legs that are each 120 degrees out of phase with each other. A leg is a separate trunk of power from the transformer. Before I go any further I feel like I should talk about voltage standards. Often you will hear the term 110, or 120, or 240. In the US the standard is 120 at the wall outlet, but because there is a 10% acceptable variance many people have just started calling it 110 and thus 220. For our purposes her I will call it 120 and 240. In a Single Phase disconnect you will have four or sometimes five lugs to tie in tails; two are hot with 120 volts each alternating in phase with each other. These are usually labeled as black and red. Electricity arrives on these lugs. Then you will have one or two neutral lugs. Most of the time both lugs are on only one neutral. The neutral is always labeled in white. The power returns on the neutral. Then of course we have the ground. The ground is a safety device, typically connected to a large metal water pipe, and is always labeled in green. If you meter between the two legs on a Single Phase disconnect you will get 240 volts. If you meter between either of the legs and the neutral or the ground, the meter will indicate 120 volts. In Three Phase there is five to eight lugs. Three lugs for the legs, which are labeled with black, red, and blue, and are carrying 120 volts each. There is almost always more than one lug for the neutral, most of the time in a Three Phase disconnect there are four neutral lugs. There is usually only one neutral line. The neutral is always labeled in white. The ground is the other lug, always labeled with green. All of the different lugs in a Three-phase panel do the same thing as a Single Phase. The big difference is what happens when you put a meter on them. In Three Phase, if you meter between either of the legs you will get 208 volts, if you meter between any of the legs and the ground or the neutral you will get 120. Three phase is often called 120/208 for this reason. Neutrals and Grounding Often when a show loads in it will have the capacity to connect two neutral lines to the venue’s power source. A sure-fire way to fry all of your gear is to drop a neutral. Once while doing a festival, a tour sound engineer accidentally disconnected the neutral on the FOH power feed. That was the last number of the show! I then spent the next five hours with the production company’s head engineer removing every piece of gear from the drive racks and changing the fuses. The power conditioners were cooked, and everything smelled like smoke. Without the neutral the electricity’s flow is interrupted, but not stopped. Everything dies! The very first thing you MUST do while tying in power is connect the ground and neutral(s), then the legs. The ground is also very important. However if you drop a ground your not as likely to fry your gear as if you drop a neutral. But, you might fry yourself. The ground is a safety feature. It gives the electricity a more attractive path than through you. Recently in Charlotte, NC, a person was killed because some work lights on some stairs were not properly grounded. For an audio guy dealing with a ground issue often means there is a hum in the system. This sometimes occurs when all of the system components are not sharing a common ground. Typically you will want all of your equipment running off of one disconnect. If that is not possible then it is best to connect the ground to a common water pipe. By most State’s law a licensed electrician is required to be on site during the connection of house power to the tour equipment. On technical riders this is often also indicated. All installed electrical connections in North Carolina (and most other states, according to the NEC) must be approved by a licensed electrician and/or inspector before it can be energized. This is very important to remember. Though these rules are often broken it is important that we are not part of these infractions. The fines can be rather high and I, for one, do not have personal professional liability insurance (a 96 dimmer rack can be pretty pricey).
Phase: How the electricity on a leg is alternating in relation to another leg. Single Phase: Two hot legs alternating identically to one another (in phase). Three Phase: Three legs each alternating out of phase with the other two by 120 degrees (out of phase) .
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