Testing Components and Controls - Switches
This is an extract from our Combination Boiler Handbook.
A typical air pressure operated micro switch is shown right. To help explain the concept of Normally open and Normally closed contacts.
Top right hand diagram
In this position current can flow from C to NC (or vice versa) but not through NO
Bottom right hand diagram
When the micro-switch button is pressed the contacts change so that current now flows from C to NO (or vice versa) but not NC
