What is a Water Heating Element?

October 9th, 2018

A water heating element is an electrically resistive loop of specially insulated wiring. In plain speak, that electrical conductor, designed to resist current flow as it is, will never be exposed, for it is carrying a dangerous charge. Instead, that wire is coiled helically and sheathed in a thermally conductive metal tube. Curiously, there’s another material inside that metal sheath, a material known as magnesium oxide.

A Cutaway Examination: Water Heating Elements 

Cutting an old and disconnected element in half, we see the wire threading its way through the centre of the element tube. It’s this part of the electrical fitting that’s electrically live. It’s also designed to balance conductivity against resistivity. After all, if the metal was a good conductor, a current would whiz through the element without generating heat. Because the wire is slightly resistive, the current entering the element terminals from the water heating system is slowed. As it slows, the resistive heating effect causes the outer metal sheath to glow red-hot, assuming the system is calling for hot water. Between those two sections, the electrical wire and outer sheath, a powdery coating, a magnesium oxide filling, transmits the heat while it also acts as an electrical insulant.

Designing Water Heating Elements 

There are, of course, many types of electrical elements. In storage heaters and fan elements, tightly wound nichrome coils use air convection and heat radiation to deliver thermal energy to the air. In water, however, that specially insulated design, as mentioned in the above passage of text, is absolutely essential because piped water is a natural electrical conductor. The resistive wire is therefore safely ensconced in its metal sheathing and that powder-filled packing. Of course, this perspective is based on a theoretical model of a typical water heating element. Real world fittings are a little different. There’s the resistive coil, naturally, for the basic principles are unchanged. Next, the packing material, the powder filling is introduced into the hollow copper sheathing, which, in turn, is coated in a zinc-plated finish. Finally, manufactured as one long loop, the element is bent and formed into an energy-efficient coil, a component that’ll fit a contemporary water heater.

Electric elements have been around for ages. Water heating elements were simply the next step in that evolutionary move. They employ the same resistive heating effect, but they don’t expose their inner workings. Submerged in water, the wire is packed in insulating powder and protected by a copper sheath, which glows hot when that inner wire resists an electrical current. In brief, they’re wonderful thermal conductors, as controlled by a system thermostat, but electrical elements are not good electrical conductors, but that’s all part of the design.

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