When designing power circuits, it is often necessary to commute two loads at once, working in different lines and connected alternately to the same voltage source. For these purposes, a conventional switch that simply breaks the circuit is not suitable. You will need a device with a more complex circuit. The well-known electrical device called “2-way switch” copes with this task perfectly. With its help, it is possible to commute lines with a wide variety of load characteristics.
The principle of operation and device
The classic two-way switch or on-off switch belongs to the same category of devices as a conventional single-pole device. However, if the latter simply closes and opens the power circuit, turning the load on or off, the electric switch to 2 positions transfers its contact from one load line to another. This is its fundamental difference from other switching elements, which naturally affects the device.
The bipolar device (in contrast to the unipolar analog) contains in its design not two, but three groups of switched contacts. One of them, called the central one, is connected in turn to one or the other direction, supplying power to various consumers. A typical example of this design is an ordinary toggle switch, which in most equipment is used only halfway - as a switch or switch. If this device uses the second direction, it turns into a cross over type device that disconnects one load from the mains and connects another.
According to the type of switching voltages, well-known 2-position switch models are divided into single-phase and three-phase models. The category of more complex designs include products that are designed for several positions at once (they are called multi-position). Two-pole two-way switches belong to devices of the same category.
Modular Three-Phase and Two-Position Switches
Devices of this class are installed in three-phase networks and allow switching the power supply to powerful asynchronous electric motors. In particular, they are used to switch a set of 3 windings from one switching circuit to another: from a "triangle" to a "star" and vice versa.
Switching the connection modes of the stator windings is necessary in order to reduce the inrush currents in the power circuits - to "facilitate" the start.
Two-position modular switches are presented in the assortment of electrical products by cam type packet switches. They are widely in demand in the following situations:
- at installation of control panels for power equipment of alternating and direct current;
- in modern power grids equipped with automatic backup systems;
- for switching winding circuits and operating modes of electric motors, as well as for controlling lighting from several points at once;
- to select suitable operating conditions for transformer substations (TP), as well as optimize the operation of their switching equipment;
- when choosing the right mode for heating equipment and welding units.
One of the varieties of on-off switches is devices that, in addition to two extreme positions, have one central one. Formally, they are referred to as three-position switches with one neutral position, but in the circuits they are still used as two-terminal devices.
For the convenience of choosing the required sample of a switching product suitable for specific conditions, the main technical parameters are indicated on the case:
- type of switching device;
- rated current for which its working contacts are designed;
- wiring diagram (switching table);
- category of protection against climatic influences.
With a switching table, it’s easy for the operator to figure out which contact groups are triggered the next time they switch.
Domestic use
In domestic conditions, the switch to 2 positions is not used as often as its unipolar analogues. But when using efficient lighting systems, there are cases in which it is almost impossible to do without these switching elements. It is about organizing the management of a common light source immediately from two or even three places in the house. Such a need arises in a situation when the light turns on at the entrance to a long corridor, and turns off at the exit from it. When installing on both ends of the switch cross over type to implement such a scheme is not at all difficult.
Another example of the importance of controlling the lighting device of their two points is when a light switch is installed at the entrance to the bedroom, and a switch is installed near the bedside table. When you press the button of the device at the entrance to the room, the group of contacts jumps to the power line of the illuminator located at its center (for example, chandeliers). When switching the second device located near the bed, other group contacts are triggered to turn it off.
It is important to note one feature of this inclusion: the order of use of each of the switches is not of fundamental importance. You can enter the corridor from either of the two ends, and turn on the light in the bedroom both from the door (at the entrance to it) and from the bedside table. You can turn it off, respectively, when laying in bed, or when leaving the room.
Another option for the domestic use of on-off switching elements is possible, consisting in installing them in three-place home lighting control circuits. In this case, you will need another switch mounted in the middle of the serviced space or in any other functionally convenient place.
An additional device is switched on according to the so-called “cross” circuit, but in fact it is still the same bipolar element. With its help, it is possible to transfer group control contacts from one direction to another.
Features of installation and connection
Before installing bipolar switches directly at their destination, it is important to determine the conditions for arranging wired lines at a particular facility (in a private house or apartment). In this case, there are two options for connecting the harness from conductors, laid either secretly or openly. With hidden laying, special grooves (strobes) are first made in the walls, into which a corrugated hose is then placed with a set of conductors inside.
In this case, the bipolar itself will have to be placed covertly - to make a special niche in the wall for it, the size corresponding to the diameter of the fastening elements. For its preparation, an electric drill with a special crown-type nozzle will be required.
It is also necessary to prepare a plastic case or mounting box in which the on / off switch will be fixed.When conducting these operations adhere to the following generally accepted rules:
- Before starting work, completely de-energize the entire apartment or go to this branch from the distribution panel by disconnecting the corresponding line circuit breaker.
- Prepare a draft layout of the switch and the conductors to it.
- After drilling a hole of suitable diameter in the wall, place the landing box in it, securing it with spacer screws.
- In the finished round niche, install the switching device itself.
- Connect the corresponding conductors to its terminals and fix the case with fixing hardware.
With the open installation of electrical wiring, it is possible to do without the tedious operations of preparing a plug and a special niche in the wall. In this case, the switch is fixed either directly on the wall, if its material is sufficiently dense and solid, or on a special lining made of plastic or wood, called a socket.
The installation procedure for an open appliance is as follows:
- Marking is made of the zone of its fixation on the wall.
- At the selected place, an additional substrate made of wood or plastic is attached to the screws (podrozetnik).
- The product is fixed on it with suitable hardware.
The procedure for connecting conductors to the terminals of the cross over device is the same as for flush mounting. With this method of laying, the lead wires can be placed in a special plastic channel called cable.
Fields of application of electric switches in two directions are not limited to the described cases. On their basis, many mechanical units are designed that control power and signal circuits.
