![]() ![]() The brackets are used to show the momentary action.Ī pair of on-off switches which operate together (shown by the dotted line in the circuit symbol).Ī DPST switch is often used for mains electricity because it switches both the live and neutral connections.Ī pair of on-on switches which operate together (shown by the dotted line in the circuit symbol).Ī DPDT switch can be wired up as a reversing switch for a motor as shown in the diagram below: Momentary (ON)-OFF-(ON) versions are also available where the switch returns to the central off position when released. It has a third switching position in the centre which is off. This is a special version of the standard SPDT switch shown above. A and B are interchangeable so switches are usually not labelled. This switch can be on in both positions, switching on a separate device in each case.įor example, a SPDT switch can be used to switch on a red lamp in one position and a green lamp in the other position.Ī SPDT toggle switch may be used as a simple on-off switch by connecting to COM and one of the A or B This is shown by the brackets around (OFF). This is the standard doorbell switch.Ī push-to-break switch returns to its normally closed = on position when you release the button, The button, this is shown by the brackets around (ON). When used with mains electricity this type of switch must be in the live wire,īut it is better to use a DPST switch to isolate both live and neutral.Ī push-to-make switch returns to its normally open = off position when you release The photograph shows a SPST toggle switch This type can be used to switch the power supply to a circuit. Motors) because they cause more sparking at the contacts when switched off. The maximum current is less for inductive loads (coils and Many times each second and an arc is less likely to form across the switch contacts.įor low voltage electronics projects the voltage rating will not matter, but you may need ![]() The AC values are higher because the current falls to zero Switch contacts are rated with a maximum voltage and current, and there may be different The momentary action is shown by using brackets like this: (ON)-OFF. This action is called push-to-make (push to close contacts). Is only momentary, as soon as you release the switch it goes back to off. A simple push switchĪ simple push-switch, such as one for a doorbell, has one set of contacts and the on position The switch mechanism has two positions: closed = on and open = off, but it is called 'single throw'īecause only one position conducts. This is type of switch is called SPST (single pole, single throw) Closed - on position, contacts conducting, there may be several on positions.Ī simple on-off switch has one set of contacts, single pole,Īnd one switching position which conducts, single throw.Open - off position, contacts not conducting.Momentary - switch returns to its normal position when released.Throw - number of conducting positions (only used for single and double).Several terms are used to describe switch contacts: ![]()
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