Switches are used to control motors, actuators, relays, contactors and consumers and to commutate control circuits in industry and households. When push button switches are equipped with a lamp, they also serve as indicators for the presence of current in the circuit.
Switches and indicators
Switches and indicators can be categorized into the following main categories:
- panel and button switches,
- rotary switches,
- isostat switches,
- rocker switches,
- foot switches,
- packet switches,
- slide switches,
- motor starters,
- toggle switches,
- indicators and indicator lights.
Panel and button switches
Buttons or button switches may be detaining and non-detaining. With detaining switches, the button remains in the position in which it was set after being presses, while with non-detaining ones, the button returns to its original position after discontinuation of the pressure. The other sign that can distinguish the two types of button switches is the number of their contacts. They can have 2, 4 or more contacts.
Furthermore, the contacts can be normally open or normally closed or various combinations of the two types, e.g. 4NO + 4NC. There are varieties of switches for 12 or 24VAC, 380VAC and other voltages. A main feature of buttons is the load that can switch. It is usually given in amperes. They can also be metal or plastic, light emitting or not, round or square. There are varieties with a latchkey, special “STOP” buttons, etc.
Push buttons are a combination of switches (mostly START / STOP) placed in a common box with protection class IP65, protecting them from dust, moisture and corrosive gas. Sometimes push buttons consist of only one button placed in a box. The box can be plastic or metal. The load, switched by push buttons is usually larger because they are designed to start and stop some kind of an engine. One of the most common applications of push buttons is operating a hoist mechanism or a crane. Therefore push buttons often consist of a combination of three buttons: up, down and stop or 6 buttons: start, stop, left, right, up, down.
Rotary switches commutate different number of positions (always more than two) through rotation. As the number of sections can be very large, and each section can have a different number of contact groups with different number of contacts, this system allows the multiple increase in the number of possible commutations. One of the most common applications of rotary switches is for switching the fan speed, radio frequency, programs of household electrical appliances such as ovens, washing machines, heaters, etc. When a rotary switch is used in PCB assembly, it is encapsulated and it is secured by a thread and a nut, and the electrical ones – by soldering the wires to pins coming out of their body.
Joysticks are manual controllers, used to actuate various devices and equipment. They move along two axes – X and Y, i.e. in one plane. They move the controlled device in directions and speed corresponding to the direction and shifting of the joystick handle. The advantage compared to, for example pushbuttons, is that the change of direction and speed of the controlled device can be performed smoothly. Sometimes joysticks are used for lifting or lowering of mechanisms. Such a device is called 2-position joystick and its handle can move only along one axis. One of the characteristic features of joysticks is the size of electrical load that their contact systems can bear, as well as the rated operational current. Joysticks are also divided into detaining and non-detaining.
Modular micro-switches for PCB assembly, for switching AC and DC circuits up to 20MHz, AC 0.04 to 1A at voltage 6 to 250VAC, and DC 0.04 to 1.5A at voltage 7 to 250VDC.
Rocker switches are one of the most common switches. Besides in control panels, they are used in many other places as part of different devices in industry and households as well as in the automotive industry. They may have one, two or three stable positions, rectangular or circular switching mechanisms. They can be light emitting. They can represent two, three or more keys in a common housing, for AC and DC, for switching different electrical loads, etc.
This category includes all pedal mechanisms with foot-controlled actuation, single or double, for switching different mechanisms and devices in industry, car manufacture and households. This type of switches control various presses, sewing machines, electric musical instruments such as synthesizers, guitars, and various cranes, electric trucks, etc. They differ by the electric load that they switch, as well as by the type of their contact systems, i.e. whether pressing the pedal stops a process or starts a mechanism.
They are micro-switches for PCB mounting, switching low-power loads in electronics. They can have the shape of a plate or a micro-switch with a very small stroke of the movable part. They can have an arm that presses the button or an arm and a roller. They can be detaining and non-detaining, their main characteristic being their very small size.
Packet switches are type of power switches designed to start, shift and stop actuators in circuits with large nominal currents. Like rotary switches, they can have a different number of sections, positions and contacts. Their main feature is the high currents which can be switched, in the range of 25-250A. By turning an eccentric body, different sections and contacts are connected, thus providing multi-variance of the electrical circuits they connect.
Packet switches directly connect, stop or reverse three-phase motors, manage various types of AC power and control circuits of stable current, corresponding to the nominal current of the switch or connect an ammeter to its corresponding current transformer in three-phase circuits. When the connected devices have authorized access, a latch switch is added to the packet switch, and when it works in an aggressive environment or subjected to moisture, dust or possible mechanical damage, it is factory-packed in a box.
Slide switches make commutation by horizontally replacing the movable key stud. They can have two, three or more positions, arranged in one line. Their main parameters are, as with other switches, bearing capacity in amperes, voltage, number of cycles and size.
Motor-starters, also called air starters are electrical devices for direct start-up, control and protection of asynchronous electric motors or other powerful consumers. Their main parameter is the voltage of the coil, the nominal current of the engine, which they switch, and the power of the controlled induction motor. They are usually placed in a metal housing, where besides the contactor there is also over-current protection, whose scope may be adjusted within certain limits. They can be installed on a wall or on the housing of the motor. They are widely used in industry, because they allow remote start-up of the motor.
The movable part of toggle switches is in the shape of a lever with two or three stable positions. The switch may be made of metal or plastics, or may be light-emitting, as LEDs are already widely used everywhere. Their electrical connection to a circuit is realized through pins, where current-conducting cables are welded. The main parameters, through which they are selected are rated current, rated voltage, internal resistance of contacts and electrical life (number of cycles).
These are lights for visual signaling with LEDs, glim lamps, neon lights, etc. Indicator lights are activated on the occurrence of a pre-programmed event, workflow or break down, as well as when there are changes in the operating mode of a machine, equipment, etc. They are usually designed for installation on a control panel and they are mounted by means of a nut or a clip. They differ by the color of light they emit, the rated voltage and the material they are made of. Their electrical connection is carried out through the soldering of a signal cable to the pins of the lamp.
The above-mentioned classification of buttons, switches and indicator lamps makes no pretence to be exhaustive but it systematizes the most common types, visually presenting the different switches and giving links to additional information regarding each presented type.