Can a 240 volt hot water heater wiring 10-3 be installed in the 100 amp sub panel? And what would cause a electric bill to be $ 500. 00 in a moble home. It seems to have went up after the 50 gallon water heater was installed. Thanks. ccedar

You should be able to install the water heater in a 100A sub panel. As far as your electric bill going up, Im not sure how much it went up so its hard to say. If it went up significantly then you may have your thermostat on your water heater way up and simply turning it down would help or you may have a short in one of the connections. You might also want to check to see if your hot water consumption isn't way up just because you have a bigger hot water heater may mean that someone is using it to its fullest and then your water bill should be up as well. If it was something as simple as the thermostat and your somewhat trying to conserve energy you might try insulating the hot water heater so it won't have to turn on as much to keep the water hot.