OT: american vs european 220

On 05/02/2011 00:42, Brent Hilpert wrote: I believe that's debatable. Now, I expect most of us would agree that voltage below about 70-90V peak (around 55V RMS) is much safer, on the grounds that while it might give a person an unpleasant surprise, a shock, even across the body, is unlikely to be fatal. Hence the SELV rules and our use of RLV 110V AC centre tapped to ground on building sites, giving a maximum of 55V RMS. (According to the standards bodies like IET, that means a maximum around 40V for indirect contact shock protection, well below the accepted standard safe touch voltage and therefore we don't need to limit earth loop impedances and worry about RCDs on building sites.) Nevertheless, I've often heard it argued that voltages around 230V RMS are safer than, say, 110V RMS, on the grounds that a casual brush with a 230V live conductor will cause a very rapid reaction in humans, often jerking the contact free, whereas voltages around the 100-150V range don't. I can't remember where I read supporting evidence, but it's certainly something I've often heard mentioned, and is one reason we think American voltages are actually more dangerous than ours. All that said, either can give a potentially fatal shock, as both are sufficient to overcome initial skin resistance. Actually, the main reason America uses split phase 120/240 is that given a 120V single-phase main supply, it's much easier and cheaper to provide 120/240 than an additional 240V single (non-split) phase or 3-phase. Just as in Europe, 240 is preferred over 120V mainly for reasons of efficiency rather than safety. -- Pete Peter Turnbull Network Manager University of York