What is the difference between using a kiln wired for 208 volts on a 240 volt circuit

If a 208-volt kiln is plugged into a 240-volt outlet, the elements will receive too much power. This usually shortens the life of the elements. If a 240-volt kiln is plugged into a 208-volt outlet, the kiln will not receive enough power and will fire slower than intended. In some cases, a slower firing will not matter, especially with large glass kilns that have plenty of power to spare. Usually, 240-volt pottery kilns that require a lot of amperages will not reach temperature on a 208-volt circuit.