Control panels have the power to start and stop machinery manually or automatically. They also offer valuable protection from overload conditions. One of the most important features includes their electromechanical assemblies and contacts, but what are electrical contacts and why are they so important in understanding control circuits? Let’s look closer at this issue to see.
What is an Electrical Contact?
Electrical contacts are two pieces of conductive metal with the ability to come together and draw apart. This action connects or disconnects conductors in circuits. When you flip a light switch to turn on a light, two sets of contacts come together. Each contact connects to a terminal, and each terminal has a wire (conductor) connected to it. The light circuit must pass through the switch to complete, and with the contacts closed, the light comes on. Turning the switch to “off” breaks the contacts apart, and the light goes off.
Contacts for Electromechanical Assemblies
Contacts in components like motor starters and contactors work the same way as simple single pole switches, except they rely on electromagnetic energy to open and close. Here is how an industrial refrigeration compressor works:
The thermostat has two sets of contacts which are normally open (apart).A spring mechanism connects to the bottom contact. Heat causes the sensitive spring to expand, pushing the bottom contact up until it touches the top contact. This sends current to the compressor contactor.
The contactor has a coil of wire which becomes magnetized when it receives electric current (like all electromechanical assemblies). This pulls the contacts together, sending current to the compressor and it comes on. When the temperature in the thermostat gets cool enough, the spring compresses and pulls the contacts apart. This stops current from reaching the contactor, and it’s no longer magnetized. The compressor loses its power and stops pumping.