Understanding switch attributes

In this article, Alan Butcher Components walks readers through some of the key attributes to consider when choosing switches.

Switches are used in a wide variety of applications from HVAC equipment and household appliances, to medical systems, audio products and power supplies. A switch’s function is to control the electric load placed on it and safely deliver the electric power required to any specific point or points on a system. When selecting a switch, there are various attributes to consider.

Switches are rated by their electrical characteristics. Current rating notes the maximum amount of current the switch is designed to carry. This rating depends on the voltage of the circuit in which the switch is used. If the maximum current is exceeded, there is a danger the switch contacts will weld together meaning the electrical circuit will no longer open. Voltage rating refers to the maximum voltage allowable in the electrical circuit where the switch is used. The voltage rating may be given as AC or DC voltage, or both.

Buyers will also need to consider the circuit’s electrical load. Load is a generic term for something that draws power. Simply put, it is the piece of equipment you turn on and off. The amount of current drawn, multiplied by the voltage equals the amount of power used by the device.

Resistive loads primarily offer resistance to the flow of current. Examples of resistive loads include electric heaters, ranges, ovens, toasters and irons. If the device is supposed to get hot and doesn’t move, it is most likely to be a resistive load.

Inductive loads are usually devices that move and normally include electric magnets, like an electric motor. Examples of inductive loads include such things as power drills, electric mixers, fans, sewing machines, pumps and vacuum cleaners.

High inrush loads draw a higher amount of current or amperage when first turned on, compared to the amount of current required to continue running. An example of a high inrush load is a standard light bulb, which may draw 20 or more times its normal operating current when first switched on.

Regarding switch action, latching means when pressed the switch activates the circuit and remains connected until the switch is pressed again. Momentary means the circuit connects when the switch is pushed and disconnects when released.

Switch cut-out is the size of the hole required within an application for the switch to fit through.

Finally, IP rating is an important consideration, particularly if an application is outdoors or used within a demanding environment.

The above are just some things to be considered when sourcing a switch. Importantly, you also need a supplier who understands the switch technology and can help you through the selection criteria.