Quoth Trumpy:
Besides, a 500W element is just that, it won't dissipate any more energy than what it is designed for.
Most of the heating elements that I've come across are simple resistors, dissipating power at E^2/R; bump the input voltage up 10%, and the power dissipated goes up by 21%.
A 500W element is _designed_ to dissipate 500W. Increase the input voltage, and the power dissipated will increase, but the element may not be able to _safely_ deal with the increased power dissipation. Increased power dissipation generally means increased temperature, which means reduced component or insulation life.
-Jon
