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| richard.cs:
--- Quote from: duak on June 24, 2020, 07:34:26 pm ---I imagine a 120 V unit would incinerate its heating element on 230 V. --- End quote --- It might survive better than you expect, a 240 V one wired wired between phases (so 415 V) seemed to work just fine, just boiled 3x quicker. :) --- Quote from: james_s on June 24, 2020, 11:50:31 pm ---200A 240V is the standard service installed in the USA, I've seen 150 and even as small as 100A service in older houses but not anything built in the last 40 years. --- End quote --- UK typical is 60-100 A, single phase, 230 V nominal, over 100 A you generally have to go to three phase but it is not common domestically. |
| duak:
Good point Richard - root 3 times the voltage is 3X the power so 1/3 of the time. 240 V is about double 120 V so we're looking at 4X the power and 1/4 of the time - providing the delta T between the element and water doesn't get too excessive. Apparently Lao Tzu said "the light that burns twice as bright burns half as long". I expect 4X the power would reduce life by a greater factor. History corner?: I sort of understand why North America has a lower nominal line voltage of 110 to 120 V is due to the Current Wars. Edison was into DC and Westinghouse and others were AC. Somewhere along the way it was legislated (although lifted later) to limit AC. A recent movie was based on it: https://en.wikipedia.org/wiki/The_Current_War I don't think Europe went into the DC dead end. Now can someone explain Japan's 100 V at 50 or 60 Hz? Cheers, |
| Gregg:
The North American standard of 120V line to a grounded neutral may have been deemed safer in the days of knob and tube wiring. Over a hundred years ago electricity in the home was mostly used for lighting and electric lights although crappy by our standards were far safer than gas lights. A common wiring method was to run the hot line across the uninsulated attic staying off the wood about an inch by the ceramic ‘knob’ insulators. The wire had minimal insulation often rubber with a cloth cover and were routed through wood via ceramic tubes. Splices were in open air, sometimes soldered, sometimes just twisted together and covered with friction tape maybe with a layer of rubber tape if you had the premium installation. A tap off the hot line was run through the ceiling to light fixtures and another wire routed down to the light switch on the wall where it switched to the neutral which was often located in the basement. Outlets were wired similarly hot from the attic and neutral to the basement. Early services were often 30 amp 120 volt with two screw in fuses that could easily be bypassed with a coin. The wire was often 14 ga powered via a 20 or 30 amp fuse because it was rated for free air to help dissipate heat. Standards back then were minimal at best and many ways were found to make this system far less safe. Things like blown in insulation, kitchen appliances, Christmas tree lights and electric heaters could easily over tax the system. It wasn’t uncommon to have a homeowner install an outlet and run the neutral to a water pipe instead of the actual neutral wire. |
| james_s:
Another factor that likely contributed to the voltage choice is that 120V incandescent lamps are substantially more efficient than 240V incandescent lamps. The lower the voltage, the shorter and thicker the filament is for the same wattage. A shorter, thicker filament has lower convective losses. A 240V 60W bulb is only slightly brighter than a 40W 120V bulb. |
| richard.cs:
--- Quote from: james_s on June 26, 2020, 04:37:43 am ---Another factor that likely contributed to the voltage choice is that 120V incandescent lamps are substantially more efficient than 240V incandescent lamps. The lower the voltage, the shorter and thicker the filament is for the same wattage. A shorter, thicker filament has lower convective losses. A 240V 60W bulb is only slightly brighter than a 40W 120V bulb. --- End quote --- Well, were more efficient, prior to the invention of the "coiled coil" filament in the 1910s. It's just a way of making a long thin filament behave convectively as a short fat one. |
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