What is average 208-230 voltage?

208V is one standard in the US for light commercial 3-phase power. It measures 208V phase to phase and 120V phase to neutral. 230 (or 240)V refers (in the US) to the common service supplied to residential. It is single-phase, with two hots and a neutral; 120-0-120. One hot and the neutral (120V) is used for receptacles and small appliances, both hots (240V) are used for large appliances, such as stoves, ovens, air conditioning, and water heater.