The Basic Motor Control Circuit Principles
Motor control circuits are widely used in industrial processes as they can provide the user with precise control over their machinery. These circuits can also have a variety of basic applications, such as the opening mechanism for an automatic garage door. Installation of control circuits should only be done by the professionals, and must be reliable if they are from the Madison Electrician Service.
Cause when you first start looking into motor control circuits, the topic can seem fairly intimidating. There’s loads of complex terminology and confusing schematic diagrams to get your head around.
In its simplest terms, a motor control circuit is a collection of switches and components that influence how a motor performs. For example, a control circuit can be used to turn a motor on or off, put it in reverse, and adjust its speed.
Although a control circuit can have a range of uses, they always contain a selection of the following commonly-used components:
- Relay Coils
The main role of relays is to control when contacts are opened and closed. A relay is an electromagnetic switch that pushes contacts together when it receives a large enough pulse of energy.
- Magnetic contactor
Magnetic contactors are specific types of relays that open or close a power circuit. When they receive the required pulse of energy, they become magnetized and attract a set of contacts, closing the power circuit. When magnetic contactors are de-energized, the contacts retreat, and the power circuit is open.
- Thermal relay
This is another type of control relay, typically used as a safety measure against high currents. If the temperature inside a motor circuit gets too high, then a thermal relay will automatically separate contacts and break the circuit. This works thanks to the direct relationship between current and heat.
- Contacts
Contacts are the most important part of a motor circuit. When contacts are connected to one another, they allow current to flow through a section of the circuit. Effectively, contacts determine when the motor is operating and when it is not.
Contacts are sometimes referred to as ‘normally open’ or ‘normally closed’. This represents the position each contact is in when the motor is in a state of rest, as you’d find them on a schematic diagram of the circuit.
- Disconnecting switches
Disconnecting switches play an important role in motor starters and circuits. They are designed to disconnect the motor from the main power supply for brief moments to prevent short-circuiting. It makes use of fuses to determine when the current is too high.
- Manual circuit breaker
A manual circuit breaker is another safety measure that will immediately stop the motor as soon as it is told to do so. Manual circuit breakers are controlled by a push-button switch that the user of a machine can easily access. Unlike a disconnecting switch, no fuse replacement is required following usage.
- Push-button switches
This is the most common type of control switch used to influence a motor circuit. Once pressure is applied to a pushbutton switch, the contacts open or close. The contacts return to being normally closed or open when pressure is released.
Why use a motor control circuit?
If you would like to have any control at all over your motor, then having a control circuit is absolutely essential. An effective control system allows the user to precisely influence how their motor is working and importantly to stay safe whilst they are doing so.
The use of overload heaters and thermal relays inside motor circuits protects the user in the case of an overload event when a dangerous amount of current could potentially be released.
