1, normal water heating with stainless steel 304, weak acid and alkaline liquids with stainless steel 316L material, strong acid and strong alkali with Teflon coating material.
2, oil heating with stainless steel 304 or iron material.
3, the resistance of the two outgoing wires should be normal should be 220V, 1000W about 48 ohms, 1500W about 32 ohms, and so on.
4, the (insulation) resistance of either outgoing wire and the shell in a few megohms or more, anyone who can be measured by the above two steps, is good.
5, air heating is more special, according to the temperature of the different choice of different materials.