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Contactors or magnetic starters are used to supply power to motors or any other devices. Devices designed to be turned on and off frequently. The connection diagram of a magnetic starter for a single-phase and three-phase network will be discussed further.
Contactors and starters – what’s the difference
Both contactors and starters are designed to close / open contacts in electrical circuits, usually power circuits. Both devices are assembled on the basis of an electromagnet, they can work in DC and AC circuits of different power – from 10 V to 440 V DC and up to 600 V AC. Have:
- a certain number of working (power) contacts through which voltage is applied to the connected load;
- a certain number of auxiliary contacts – for organizing signal circuits.
So what’s the difference? What is the difference between contactors and starters. First of all, they differ in the degree of protection. Contactors have powerful arc chutes. Two other differences follow from this: due to the presence of arc extinguishers, contactors are large and heavy, and are also used in circuits with high currents. For small currents – up to 10 A – only starters are produced. By the way, they are not available for high currents.
There is one more design feature: starters are produced in a plastic case, only contact pads are brought out. Contactors, in most cases, do not have a housing, therefore they must be installed in protective housings or boxes that will protect against accidental contact with live parts, as well as from rain and dust.
In addition, there is some difference in purpose. Starters are designed to start asynchronous three-phase motors. Therefore, they have three pairs of power contacts – for connecting three phases, and one auxiliary, through which power continues to flow for engine operation after the “start” button is released. But since such an algorithm of operation is suitable for many devices, a wide variety of devices are connected through them – lighting circuits, various devices and devices.
Apparently because the “stuffing” and the functions of both devices are almost the same, in many price lists the starters are called “small-sized contactors”.
The device and the principle of operation
In order to better understand the connection diagrams of the magnetic starter, you need to understand its device and the principle of operation.
The basis of the starter is a magnetic circuit and an inductor. The magnetic core consists of two parts – movable and fixed. They are made in the form of the letters “Ш” installed “feet” to each other.
The lower part is fixed on the body and is fixed, the upper part is spring-loaded and can move freely. A coil is installed in the slot of the lower part of the magnetic circuit. Depending on how the coil is wound, the value of the contactor changes. There are coils for 12 V, 24 V, 110 V, 220 V and 380 V. On the upper part of the magnetic circuit there are two groups of contacts – movable and fixed.
In the absence of power, the springs squeeze the upper part of the magnetic circuit, the contacts are in their original state. When voltage appears (the start button is pressed, for example), the coil generates an electromagnetic field that attracts the upper part of the core. In this case, the contacts change their position (picture on the right in the photo).
When the voltage fails, the electromagnetic field also disappears, the springs press the moving part of the magnetic circuit upwards, the contacts return to their original state. This is the principle of operation of an electromagnetic starter: when voltage is applied, the contacts close, and when voltage is lost, they open. Any voltage can be applied to the contacts and connected to them – even constant, even variable. It is important that its parameters are not more than those declared by the manufacturer.
There is one more nuance: the starter contacts can be of two types: normally closed and normally open. From the names follows their principle of operation. Normally closed contacts are disconnected when triggered, normally open contacts are closed. The second type is used to supply power, and it is the most common.
Connection diagrams for a magnetic starter with a 220 V coil
Before we move on to the diagrams, let’s figure out what and how these devices can be connected. Most often, two buttons are required – “start” and “stop”. They can be made in separate cases, and may be a single case. This is the so-called button post.
With separate buttons, everything is clear – they have two contacts. Power is supplied to one, it leaves the second. There are two groups of contacts in the post – two for each button: two for start, two for stop, each group on its own side. There is also usually a ground connection terminal. Nothing complicated either.
Connecting a starter with a 220 V coil to the network
Actually, there are many options for connecting contactors, we will describe a few. The scheme for connecting a magnetic starter to a single-phase network is simpler, so let’s start with it – it will be easier to figure it out further.
Power, in this case 220 V, relies on the coil leads, which are labeled A1 and A2. Both of these contacts are located in the upper part of the case (see photo).
If you connect a cord with a plug to these contacts (as in the photo), the device will be in operation after the plug is inserted into the socket. At the same time, any voltage can be applied to the power contacts L1, L2, L3, and it will be possible to remove it when the starter is triggered from the contacts T1, T2 and T3, respectively. For example, inputs L1 and L2 can be supplied with a constant voltage from the battery, which will power some device that will need to be connected to the outputs T1 and T2.
When connecting single-phase power to the coil, it does not matter which output to apply zero, and which phase. You can switch wires. Even more often, a phase is supplied to A2, since for convenience this contact is also brought out on the underside of the case. And in some cases it is more convenient to use it, and connect “zero” to A1.
But, as you understand, such a connection scheme for a magnetic starter is not particularly convenient – you can also directly supply conductors from the power source by integrating a conventional knife switch. But there are much more interesting options. For example, you can supply power to the coil through a time relay or a light sensor, and connect a street lighting power line to the contacts. In this case, the phase starts at the L1 contact, and zero can be taken by connecting to the corresponding coil output connector (in the photo above it is A2).
Magnetic starters are most often set to turn on the electric motor. It is more convenient to work in this mode if there are “start” and “stop” buttons. They are connected in series to the phase supply circuit to the output of the magnetic coil. In this case, the circuit looks like the figure below. note that
But with this method of switching on, the starter will only work for as long as the “start” button is held down, and this is not what is required for long-term engine operation. Therefore, the so-called self-pickup circuit is added to the circuit. It is implemented using auxiliary contacts on the starter NO 13 and NO 14, which are connected in parallel with the start button.
In this case, after the START button returns to its original state, power continues to flow through these closed contacts, since the magnet has already been attracted. And power is supplied until the circuit is broken by pressing the “stop” key or by triggering a thermal relay, if there is one in the circuit.
Power for the motor or any other load (phase from 220 V) is supplied to any of the contacts marked with the letter L, and is removed from the contact located below it marked T.
It is shown in detail in what sequence it is better to connect the wires in the next video. The whole difference is that not two separate buttons are used, but a button post or a button station. Instead of a voltmeter, it will be possible to connect an engine, a pump, lighting, any device that operates on a 220 V network.
Connecting a 380V induction motor via a 220V coil starter
This circuit differs only in that three phases are connected to the contacts L1, L2, L3 and also three phases go to the load. One of the phases is started on the starter coil – contacts A1 or A2. In the figure, this is phase B, but most often it is phase C as it is less loaded. The second contact is connected to the neutral wire. A jumper is also installed to maintain power to the coil after the START button is released.
As you can see, the scheme has not changed much. Only it added a thermal relay that will protect the engine from overheating. The assembly order is in the next video. Only the assembly of the contact group differs – all three phases are connected.
Reversible motor connection scheme through starters
In some cases, it is necessary to ensure that the motor rotates in both directions. For example, for the operation of a winch, in some other cases. A change in the direction of rotation occurs due to phase reversal – when one of the starters is connected, two phases must be reversed (for example, phases B and C). The circuit consists of two identical starters and a button block, which includes a common “Stop” button and two “Back” and “Forward” buttons.
To increase safety, a thermal relay has been added through which two phases pass, the third is supplied directly, since protection for two is more than enough.
Starters can be with a 380 V or 220 V coil (indicated in the characteristics on the cover). If it is 220 V, one of the phases (any) is supplied to the coil contacts, and “zero” is supplied to the second from the shield. If the coil is 380 V, any two phases are fed to it.
Also note that the wire from the power button (to the right or left) is not fed directly to the coil, but through the permanently closed contacts of another starter. Contacts KM1 and KM2 are shown next to the starter coil. Thus, an electrical interlock is implemented, which prevents the two contactors from being energized at the same time.
Since not all starters have normally closed contacts, you can take them by installing an additional block with contacts, which is also called a contact attachment. This prefix snaps into special holders, its contact groups work together with the groups of the main body.
The following video shows a connection diagram for a magnetic starter with a reverse on an old stand using old equipment, but the general procedure is clear.