Em 3/6/2010 19:36, Michael Watterson escreveu: > 110V AC is actually about 140V peak. Building sites here have to use = > = More like 155.56V. > centre tapped earth 110V AC via certified transformer for safety, which = > would be 70V peak to ground. (Household electric here is all 220V to = > 230V AC 50Hz). > > So someone decided that the the safe limit is over 70V (assuming a = > margin) and using 12V batteries (or 6x 2V cells in one case) they = > decided a nominal -48V is probably worst case 65V to 70V (56V normal = > full charge. Adding another 12V (nominal 60V instead of 48) would be = > 70V at full charge and about 85V if battery fault and charger running. > > You don't want to stand in a wet trench with maybe 85V :( > > I'd always been told in College and BBC that the nominal -48V was = > highest nominal system volts for safety (bearing in mind it's not = > actually -48V or -50V historically, but from 24 x Lead Acid cells or 4 x = > lead acid Truck/car batteries). Which obviously would be a lower voltage = > than the generally regarded safe voltage. > = IEC defines several levels of safety voltages: Regards, Isaac __________________________________________________ Fale com seus amigos de gra=E7a com o novo Yahoo! Messenger = http://br.messenger.yahoo.com/ = -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist