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Old 01-27-2016, 10:13 AM   #41
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I read this a while back about 110v vs. 120v. Made sense of the history...

"110V" is a legacy resulting from systems in the earliest days of electrification using AC distribution systems developed by Tesla for Westinhghouse. They had to compete with Edison, who was promoting DC for his electric lights, and through a series of experiments, he had settled on 100VDC as a compromised between safety and lumen output. So to make people willing to use AC, Westinghouse decided on 110VAC as a standard. I've read somewhere that he may have started out with 100VAC, but changed it to 110 because it sounded "better" than 100, kind of like the volume knob that goes to 11.

In the early days, once people started jumping all over the concept of long distance distribution of AC, there were different system voltages at almost every provider, ranging everywhere from 100-135V. That presented a challenge for equipment providers, especially those using motors, because a motor designed for 100V is going to fry at 135V. So over time, equipment vendors organized to try to force standards of conformity (the beginnings of NEMA). At first they settled on 117V +-10% as a compromise because the +- range works from 100-130V. If you look on 1920s vintage motorized devices in antique stores, you will often see them listed as 117V.

In the 30s, the REA (Rural Electrification Act) was enacted with the purpose of extending electrical service to farms and small towns, partly as a way to increase productivity. Because the REA administration did not want their work crews to have to carry multiple different transformer designs around in their trucks, they forced a settlement on 120/240V as the "DISTRIBUTION" voltage, meaning what the utility delivers, with 115/230V as the "UTILIZATION" voltage, meaning what the end device is designed for, acknowledging that there will be some voltage drop by the time it gets to the device. Later, those values were adopted by ANSI as the official standards. Those are the official standards to this day.

But still, the utilities that actually GENERATED AND DISTRIBUTED the voltage were not actually forced to change existing systems, they just had to used those standards for NEW systems. So to this day there are still pockets of legacy voltage levels in different places, which adds to the confusion all around. I don't personally know of any "110/220V" systems here in California, probably because the REA got here late. But I have been told they still exist.

As to 3 phase, it is 120/208, because 208 divided by the sq. rt. of 3, which is the phase to neutral voltage of a Wye transformer, is 120. Same for 480/277. Along the same lines of the residential voltage levels, there are older legacy systems for industrial use that are 440V, 450V, 460V, 550V and 600V, but officially it is now 480V dist., 460V util.
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Old 02-02-2016, 11:14 PM   #42
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Had some delays due to weather and wind, but the building was completed yesterday. Power applied and all is good. The final measurement was 122 feet of 6/3 wire. The electrician who did the final hookup used some sort of meter/test device that said the total voltage drop was 0.7.
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Old 02-03-2016, 07:05 AM   #43
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Quote:
Originally Posted by emm-dee View Post
Had some delays due to weather and wind, but the building was completed yesterday. Power applied and all is good. The final measurement was 122 feet of 6/3 wire. The electrician who did the final hookup used some sort of meter/test device that said the total voltage drop was 0.7.
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