Household Appliances Heating up Elements In

A huge variety of household appliances contain heating elements. The two basic types are the exposed single-wire element, most often used in hairdryers, fan heaters and toasters, and the metal-sheathed element used in ovens, grills, iron sole plates and immersion heaters.

Exposed element

This type of element is simply an exposed length of conductor which heats up when a current is passed along it due to the resistance properties of wire. As it is an exposed conductor, it must be housed and supported in a way that avoids accidental contact which could cause electric shock or burns. It must also be housed in a way that allows the heat generated to dissipate and do the job intended. For instance, a toaster needs a large aperture in which to place the bread so that it rests near the exposed element for it to function correctly.

Covered element

The metal-sheathed or shrouded element can be shaped during manufacture into a multitude of configurations to suit virtually any application because of the way it is both insulated and supported by its solid outer sheath.

It works in the same way as the exposed element, but the conductor is housed within a tube and surrounded by insulating material (magnesium oxide). Heat is transferred to the outer sheath but the current cannot pass. The outer sheath may be made from various metals to suit particular requirements and conditions. Some are designed for use with the heating portion of the element submersed in water, as in kettles, immersion heaters and showers. Others, used in cookers and sandwich makers, for example, are designed to radiate heat.

The temperature may be controlled in several ways.

Common faults

One of the commonest faults is that of open circuit, that is, no current flows through the heater so no heat is produced. This may be due to a broken or loose connection to one of the heater terminals. This then overheats, leaving an obvious discolouration of the connection or terminal and resulting in a break in the circuit at that point. Alternatively, the break in the circuit may occur within the element itself. Test for continuity as described in the section Electrical circuit testing.

Another fault is low insulation. Accompanying this fault is that of the short circuiting of the heater caused by a complete breakdown of insulation. This results in the appliance `blowing’ fuses or earth tripping if it is an earthed appliance. If any of these faults occur, a complete replacement of the component is required.

Replacement parts

Two basic terminal types are found on solid elements and are shown here together with support plate fixing variations. Those above are used for cooker elements while those below are used on submersible elements such as kettles.

Many elements are readily available as spare parts and blister-packed for ease of identification. Make sure you buy an exact replacement which matches the original in every way: size, type of fitting and wattage. New seals will be required to replace those disturbed during repair of such appliances as kettles and coffee makers.

As always, before commencing any checks or repairs make certain the appliance is isolated: switch off, plug out. Clean all the connections thoroughly and renew any connections that are at all suspect or any that are overheated. Failure to do this will quickly lead to problems because of the high current draw of heating elements.

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