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[quote]QUOTE: Originally posted by cacole Ian, Do you know any of the historical background as to how Australia wound up with 240 Volts as the mains standard? In my 26 years of travels around the world in the U.S. Army I encountered voltages from 90 to 220, and Hertz from 50 to 400. 220 Volts at 50 Hz seems to be the most common throughout Europe, with 90 to 100 Volts at either 50 or 60 Hz throughout the Far East (Japan, Okinawa, Korea, and Vietnam). In the U.S., nearly everyone says our current is 110 Volts at 60 Hz, but it's actually 117 Volts peak-to-peak. 110 Volts is the RMS reading. [/quote] NOT!!!!!!!! Some electrical education for the masses, and some things you never knew and maybe NEVER wanted to know...... First, AC voltages are measured RMS, except possibly in a lab where they're using an oscilloscope. It is a pretty clean sinusoidal waveform, unless harmonics are introduced into the system. The square root of 2 comes into the calculation when comparing peak vs. RMS voltage. A 120 volt signal will have a peak voltage of positive 170 volts and minus 170 volts. It wiggles back and forth at 60 times a second here in the U.S. Some say it must be a woman because it can't decide what it wants to be.... ;-) Another confusion factor is that you CAN have a peak-reading RMS voltmeter! This does not measure the peak voltage of the waveform (170 volts) but the peak RMS voltage measured over the period of time that you have the meter attached. This comes in handy when you're watching the line voltage bounce up and down. They also have minimum-reading meters as well when you want to know how bad the voltage sags when a motor kicks on. These same meters can be used to measure the peak and minimum DC voltages as well, so you could hoook them up to your rails and REALLY know what was happening to your system, handy, eh? These meters won't however do a decent job reading the actual peak transient voltage that rides in on your system. A lot of effort is put into preventing harmonics from getting into the power system, as harmonics can sap a bunch of energy out of the system by heating up transformers and such before it even gets you your house. Harmonics are created by basically any energy-efficient or consumer-friendly piece of equipment out there. Flourescent lights, dimmer switches, computers, etc. Motors and standard incandescent lights are clean. Variable speed motor drives are TERRIBLE, but they do make life more comfortable and energy efficient. Standard single-phase voltage for residential use is 240/120, plus or minus 5% as per ANSI standards, AVERAGE volts that is. That means anything between 126 and 114 volts RMS is within tolerance at the METER to your house. In addition to that, an additional 4 volts drop is allowed before you hit the equipment you plug in. In other words your equipment has to be able to operate on anything from 126 down to 110 volts. In addition to that you can expect as much as a 4% short term sag in your voltage whenever a large motor kicks on at a neighbors house. If you have a large motor kick on you could see an even greater sag than that. This falls into a voltage flicker standard, that is not codified into an ANSI standard, but is from generally accepted data put together by Westinghouse back in the 1950's. On top of all THAT you have the potential of some very fast disturbances of either high or low voltages whenever the utility switches large transmission lines or capacitor banks. You could see voltages of DOUBLE the normal line voltage for a fraction of a waveform, multiple times a day. These tollerances fall into what cas been called the CBEMA operation curve for electronic equipment. I haven't even got into what Mother Nature can throw at you..... Anybody's head spinning yet? Mark in Utah (Electrical engineer & utlity guy)
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