For example 120 240 and 120 208 both provide 120v on standard receptacles but when using a dryer or hot water heater for example that appliance would be using 240v or 208v respectively.
Will a 240v heater run on 208v.
When you run 120 208v single phase power into an isolation transformer the two individual hot conductors of 120v are combined into one 208v waveform.
The important dfference othere than maybe having too high or low a voltage is that one of the input leads is either ground referenced or both are hot.
Therefore if you put 120v in you will get 120v out 208v in gets you 208v out 240v in gets you 240v out etc.
220v is a line to ground voltage of a 380 220y system.
It will take longer to heat your water with less wattage.
Say the tank draws 20 amps.
It is more likely a 208v 230v or 240v motor.
208v is a line to line voltage of a 208 120y system.
Putting it all together.
Some motors are actually dual rated for both 50 and 60 hz with corresponding different speed and amp ratings.
20a x 208v 4160 watts.
Can run 208v heater on 240v.
20a x 240v 4800 watts.