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One Leg or Two?

Dear Swami, If a load draws 10 amps at 208 volts, is that 10 amps per leg or 10 amps total?? I recently worked on a show where I calculated 10 amps total and I was shocked to find I was short of amps. Please clarify. Signed, Shorty Dear Shorty, What you have done is a classic miscalculation when you are using 3-phase power. When you connect a 208V load across two legs, you are completing a circuit in which the current is passing through both legs, therefore that would be a total of 20 amps. But something happens when you connect a second 208V load that is not using the same two legs of your 3-phase system. It will also draw 10 amps through both legs, and since one leg will be shared (there is no other option), then the current passing through the shared leg is the combination of the 10 amps being drawn by one of the loads and 10 amps being drawn by the other. The trick is that the currents are 120 degrees out of phase with each other, meaning that the alternating current wavefo...
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Amps Are All Askew

Dear Swami, I'm stumped (and so is everyone I've asked thus far). I can't seem to figure out the power draw on a show. Here's the layout: 15 - VL4k spots @ 208V; 16,000W each = 24,000W 3 - Clay Paky Alpha 800 @ 208V;  1200VA each =  3600W (assuming PF = 1) 12 - S4 Series 2 Lustr @ 208V; 168W each =  2016W 3 - Colorado Solo1 @ 208V; 62W each =  186W So that's: 24,000   3,600   2,016      186 29,802W total   The incoming voltage from the service is about 117V phase-to-neutral and about 202V phase-to-phase. When I do the math (29,802W ÷ 202V), I keep coming up with 147.5A total, or 49 amps per leg in a balanced 3-phase system. What my meter is telling me is about 82 to 86 amps with every light in the rig on full. Unfortunately, audio and video are using the same service, so that pushes it up to the low 90s range, and it's a 100-amp service, so it is way too close. Am I missing so...
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Which direction do you coil cable?

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Dear Swami, I'm working on a show with some electricians who insist that feeder cable should be coiled in a clockwise direction, but I think it depends on the cable. What's the proper direction to coil cable? Signed, Coiling in Columbia Dear Coiling, Does the sun rise to your right or to your left? Like the direction of the sun, the direction to coil cable depends on which way you are looking at it. To get it right every time, follow the natural coil of the cable. If it wants to coil clockwise, coil it clockwise. If it wants to coil counter-clockwise but you want to coil it clockwise, then flip it over and coil it clockwise. Either way, the sun will shine upon you. Signed Swami Candela of the Third Millennium
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The Angle of the Dangle

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Dear Swami,   I’m working on a show where some electricians use their slip-joing pliers (AKA, Channellocks) to twist cam-lok connectors on my feeder cable. They all think the plastic insulators have to be 180 degrees offset when the connectors are mated. I’ve combed through the cam website, but the best I can find so far is that there are no tools needed to install. Are there any resources describing the proper mating angle?   Signed, Twisted in Toledo   Dear Twisted,   What we in the entertainment industry generically call camlocks (or cam-loks) are single-pole locking connectors. Cam-Lok is the Cooper Industries brand name, which includes a range of different types. The type we commonly use in entertainment is the J-Series E-Z1016, which can accept 2/0 or 4/0 cable, and it’s rated for up to 600V and 400 amps of continuous duty. If you look at the specs for that connector, it says that it provides up to 600 pounds per square inch of contact pressur...
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Support for Women

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Dear Swami, I've read that you should never wear metal jewelry or any other metal when you're working around live exposed conductors. But where can I find a bra that will give me the support I need without an underwire? Signed, Seeking Support in Suburbia Dear Seeking, More women are working as live event production electricians, and the Swami supports gender equality in the workplace. That includes arc flash protection as well as every other protection afforded any other worker. It turns out that there are arc rated bras, just as there is arc rated clothing. They are available anywhere you can buy arc rated clothing, including online retailers like ArcStore (www.arcstore.com). For example, the ArcBra is compliant with NFPA 70E and is rated 8 calories/square centimeter. Like other arc rated clothing, it's not cheap, but it certainly is worth the protection it affords. Signed, Swami Candela of the Third Millennium
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Segregating DMX

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Dear Swami, I've heard people say that you should separate fixture types on their own DMX line or they will not work properly. Is that true? Signed, Lines Crossed in Dimmer Land Dear Crossed, The sky is dotted with clouds that color truth. DMX is well defined and as long as the maker of the machine follows the path of the protocol it will take flight. There is no technical reason for segregating DMX fixtures by type, although there may be historical reasons. In the early days of automated lighting, Martin used an non-compliant pinout and swapped pins 2 and 3. If you used an adaptor it would work with any other DMX devices. Old habits are like the weeds that grow between the cracks in the sidewalk. To be rid of them is hard. There may be other reasons for the practice of segregating DMX by fixture type but it has nothing to do with compliant fixtures.
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Resistance is Futile

Dear Swami, How does one find the cross sectional area of a cable? In the book, "Electricity for Entertainment Electricians & Technicians," there is a formula in Appendix 4 to calculate voltage drop, and it uses the cross sectional area of the cable. Can you point me in the right direction? Signed, Looking for Direction Dear Looking, The universe is a bountiful source of information, but the internet puts it at your fingertips. For American Wire Gauges (AWG), you can find the cross sectional area of solid wire in Wikipedia on this page  and for international wire sizes, they are spelled out in IEC 60228. Two things to remember: 1. The cross-sectional area of stranded wire is calculated by adding all of the cross-sectional areas of the individual strands of solid wire that make up the stranded wire, and 2. The resistance of copper wire varies according to its temperature. The wire gauge charts typically use 30 degrees C (about 86 degrees F) as the ambient air t...
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