Ask Swami Candela

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...

Dear Swami, A portable generator supply company supplied a generator for a show and told me to use the building ground since the generator is not close enough to any earth to pound in a grounding rod. I believe their generator is ungrounded because they only supplied three hot conductors (black, red, and blue) and a neutral conductor (white) with no grounding conductor (green). Does the generator need to be grounded? Do they need to provide a true earth ground that is bonded to a grounding rod? Or can they use the ground from the building to ground the generator? Signed, Floating Above Earth Dear Floating, The laws of man vary according to location, but the laws of nature are immutable. You should follow the local codes and regulations dealing with driving a grounding rod, but never violate the laws of nature, common sense, and safety. The reasons for grounding are three-fold: 1. to limit voltages due to lightning, line surges, or unintentional contact with higher voltage ...

Dear Swami, How do you 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. It says, V D = (2KIL)/(#A CM ), where K = the specific resistance of copper [12.9 at 75 degrees C (116 degrees   F) or 11 at 32 degrees C (90 degrees F); I = current in amps; L = the length of the cable in feet; # = the number of conductors per phase; and A CM = the area of the cross section of the cable in circular mils. Where can I find the area of the cross section of the cable? Dropping Volts in Downtown Detroit Dear Dropping, Congratulations for having gotten that far in the book! If you are wondering about how to calculate voltage drop then you probably already know how important it is to keep your volts up and your amps down. As Bob Dylan once said, "The answer my friend, is blowing in the wind," if by "wind" he meant in the wire gauge charts...

Dear Swami,   I am starting to see a lot of lights and consoles that have RDM (remote device management), and I'm wondering how that will affect the practice of terminating data runs. If I'm setting up a lighting system and I'm using RDM, do I still need to terminate the last fixture in the run? And do I have to have a 5-pin data cable to make it work?  Signed, Terminally Wondering Dear Wondering, Almost all of the new products that are being manufactured today have RDM, so you will see being used more and more in future shows. RDM uses the same cables, connectors, and pin-out as DMX, so the only difference between setting up a DMX data distribution system and an RDM system is that instead of using a DMX splitter you will need an  RDM splitter or RDM hub, like the ELC  DT125 or similar . DMX splitters are uni-directional and RDM is a bi-directional protocol, so DMX splitters will not send data back to the console(s). To see a short video of Bill Ell...