Why did the US standardize on 110/220 volts? Does it have advantages over the UK’s 240 volt system?

The US system is 120/240V at 60 Hz. The 120V standard does not really have an advantage over 240V.

The 120V system is perfect for causing ventricular fibrillation which if it persists causes death , while the 240V system is slightly more likely to clamp the heart which has a slightly lower chance of being fatal as the heart can sometimes spontaneously go back into normal rhythm after clamping. This of course is dependent on moisture and other factors, but on average 240V is actually slightly safer.

The current usage on the UK system is lower per circuit, this means smaller wires can be used. In a single house this won’t make much of a difference, but in an entire country it can save a lot of copper. In our US system, we have to use more copper inside the house for the same power delivery.

There is a slightly higher chance of arcing with the 240V system, but in dry air the arc distance goes from roughly 0.13 mm at 120V to 0.26 mm at 240. In normal building wiring this difference is negligible.

As to why 120V was chosen in the US, my guess is that it’s probably related to Edison’s initial DC system that was a three wire system: +110V, 0V, and -110V. The same wiring could be reused for 120VAC and deliver the same amount of power. In some ways it’s early adopter syndrome.

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