[AllanJ]

Two hundred eight volts is found only in 3 phase systems with a neutral to provide 120 volts (hot to neutral). When the phase to phase (hot to hot) voltage is actually about 240 and a neutral provides hot to neutral voltage of about 120 for some (two) of the phases then you get 208 volts from the third phase to neutral and that 208 volts is not intended to be used for anything.

They do not make light bulbs specifically for 208 volts. You wire up the light fixtures to use 120 volts. On 208 volts you use 220 to 240 volt incandescent bulbs (or hit or miss with 220 tio 240 volt LED or other kinds of bulbs) only if you absolutely have to.

On 120/208 volt (wye; symmetric neutral) 3 phase systems, the 208 volts phase to phase (any two hots) is used "like" it was 240 volts. There are still a few exceptions where 240 volt appliances or devices do not work well, which cases are hard to predict.

When a home is supplied with 120/208 volt 3 phase (often with just two of the three hot lines) the wire gauge rules are the same as for 120/240 volts, including if all 3 phases were supplied and a 3 phase multiwire branch circuit (all 3 hots and ground and shared neutral) were strung in the wall.

 

[AllanJ]

I beg to differ. In any 3 phase system, if two hots are used to feed a motor or other device and a third supply conductor as a neutral (whether or not present) is not incorporated into the circuitry, then the power received by the device is also theoretically a pure (think: balanced) sine wave although at the voltage (e.g. 208) thought of as "odd" by someone just getting acquanted with 3 phase power. (When the AC peak is reached on one leg while the valley has not yet been reached on the other leg due to the 120 degree phasing relationship, the result is still a sine wave. The "other" leg will eventally reach valleys and peaks of the same magnitude as those reached by the first leg.)

Given an ancient Edison direct current power station providing plus 100, minus 100, and neutral (zero referenced), I find it hard to believe that equipment and especially light bulbs and motors were designed back then (1900) to allow indiscriminate use on either 100 volts (hot to neutral) or 200 volts (hot to hot). The design of devices including refrigerators would be somewhat complicated and not worth the expense.

Instead it would be much more reasonable to provide each customer (each home) with hot and neutral at 100 volts as the service. The practice of supplying neutral and one hot persisted proliferously well into the alternating current era in the U.S., with what is still referred to and in some cities still available as two wire 120 volt service.