Three-position switch - an electromechanical switching device used in electrical engineering to switch power to another line in case of overload. It is also used to conduct electric current in the normal mode and periodically turn on the electrical circuit.
Principle of operation
The 3-position switch has a 3-position handle for opening and closing the chain. The middle position allows each existing contact group to open. The user controls the device manually. The upper contacts are usually used to connect inputs, and the lower ones are used for loads. Such a device is not equipped with releases (thermal or electromagnetic), so when it is installed, automatic switches are placed on the inputs, which are triggered by an overload. This configuration will prevent sparking incidents and damage to the integrity of the wiring insulation material. In the past, these devices have been used as input masters in switchboards. Over time, this place was taken by automatic circuit breakers, but the flexibility and simplicity of the design of position switches, as well as their low price, provide these products with sufficient popularity.
Varieties of three-position switches
3-position electrical switches are available in a variety of designs. Some models are equipped with a latching switch position option. They are equipped with a key lock mechanism, which excludes spontaneous transition to another position. Others, which do not have this function, independently return to their original position. The design of some devices provides for the presence of a zero position - it involves the separation of all contacts.
Usually, products are manufactured for operation in power grids with a nominal current of 25, 16 or 10 A. As for the voltage, for direct current its value can reach 220 V, for alternating current - up to 500. The devices are equipped with markings showing the power level and protection category.
The most common design is a 3-position mechanical stack switch. Their control element is not a button, but a handle. Modern models are equipped with ergonomic handles designed to prevent fingers from slipping. Products are of two types - biscuit and cam.
The cam device also includes a series of packages, but arranged in a different way. Moving contacts are located on the outer sides of the plates connecting to the body, and static contacts on the inner sides. The first of them look like bridges with springs. Their position is regulated by a rod mechanism that changes position under the action of the cam. In the latter, in turn, the position is changed by means of a handle and a shaft. Both in the case of biscuit models and in devices with cams, the shaft can have a different number of positions (up to eight). In three-position devices, their number is equal to three.
The switch can be mounted on a DIN rail, on a wall, in a cabinet, depending on the model. Explosion-proof products used in industries posing a danger to human health are produced. Most 3-position switches, however, are susceptible to explosions, temperature extremes, and do not tolerate moisture. The degree of sensitivity of the device to environmental conditions can be determined by its appearance: if the product is open, devoid of a protective case, it is highly sensitive, it should be installed only inside the panel in a room with dry air. Switches with plastic or metal housing and touch-proof clamps can also be installed outside the switchboard.
If the housing is hermetically sealed, the device may be installed even outdoors. During operation, weak mechanical influences and vibration are allowed (no more than 35 Hz).
The advantages of the devices include operational reliability, wear resistance and a fairly low price. They suppress electric arcs very quickly, but withstand a limited number of overload operations. The weak point of these products in comparison with circuit breakers is also their limited possibilities as a protective device: they do not protect against short-circuit incidents. Also, mechanical switches cannot be repaired: if the product has become unusable, it is dismantled with subsequent disposal, and a new one is installed in its place. They fail relatively quickly, although some manufacturers claim that the device can withstand up to half a million switches.
Household use
There are many applications for 220V three-position switches in industry and everyday life:
- control of light and transformer substations;
- switching programs for the operation of electric welding, heating and other production equipment;
- manipulations with the modes of electric motors;
- remote control of asynchronous electric motors;
- automatic input of a reserve;
- switching in panel devices.
Also, these products are used for power supply of substations, for example, in grounding structures, switching measuring instruments.
How to connect
During Soviet times, the use of a three-position switch for the power supply of apartment buildings was widespread and widespread. Then they were installed in distribution boards. Now, instead of such devices, automatic ones are more often used. If the owner chooses to use a three-position, three-phase switch, it can be installed in front of the electricity meter leading to the switchboard so that the apartment network can be turned off completely if the need arises. Also, to strengthen the protection of the network from overload or short-circuited incident, it is possible to recommend the combined use of both devices.
When installing the device in a private house with a modest electricity consumption, as well as in the country, a single-phase circuit can be used, which includes the device in the home electrical network of a spare source. Indicator lamps should be placed inside the shield, signaling that the network or generator is turned on.
Connection diagram
When purchasing cables for mounting a three-position device, it is necessary to take into account the maximum values of the operating current in the electrical circuit. If the diameter of the conductors exceeds 6 mm2, special ferrules are purchased for them. Less thick wires are allowed to be connected directly to the device using soldering or ring stripping.
Typical diagrams suitable for a particular device, including a diagram for connecting a switch from three different locations, are given in the technical documentation attached to it. Some of the three-position products can be connected not only to 3 poles, but also to 1, 2 or 4 (the possible number of poles is indicated in the device passport). At the entrance to the apartment, the device is placed at the outlet from the common phase conductor and zero in order to separate the apartment line from the main line. The installation of the switch and its subsequent adjustment is possible only when the electricity is turned off. Modern products designed for use in apartment boards usually involve mounting on a 35 mm DIN rail. Their terminal clamps are marked with numbers, which avoids confusion during the installation work. After installation, the device, as well as the adjacent contact connections, must be cleaned with a dry cloth at least once every 6 months, having previously disconnected the power supply.
As a device for switching a home network, positional hand switches are often considered obsolete. However, their ease of operation and installation, as well as their price, have given them some popularity to this day.
