The difference between a thermal and motor breaker, why a thermal, why switch of

Hello, I am a beginner mechatronics who recently pokes something in automation and I have many basic questions
-How does the phase loss sensor work, I heard that it can be done by itself on two relays, could someone send me a diagram of such a phase loss sensor made on 2 relays?
- Since the motor switch disconnects the circuit when the current consumption is slightly higher than the rated motor current, why then we also use thermics (I do not know what is the professional name, thermal relay?)
-Why does the motor circuit breaker not disconnect the circuit when starting the motor when the starting current is even 8x higher than the rated one?
-Why do we sometimes use a phase loss sensor if we have a thermal switch?

If anyone would have any interesting materials / videos / channels on Automation and concepts to help them understand the topics related to it, I was grateful for sharing them with me. And if anyone would have any nice trivia or useful information, please also share them.
Regards

In a nutshell:
- The thermostat is to provide protection against long-term overloads e.g. the motor is mechanically overloaded by a broken bearing
- The miniature circuit breaker is mainly used for short-circuit protection. It does not disconnect the circuit because it is its characteristics that it withstands several times higher currents for a short period of time
best compare yourself time-current characteristics of overcurrent circuit breakers and thermistors.
- The protection against phase loss is made on the basis of the adder and the relay control system, when the voltage at the output of the adder is too low disconnects the relay.
- It can be done, but two relays are not recommended because they must be 400V and one of them connects between L1 and L2 and the other between L2 and L3 and the contacts connect in series. But I do not recommend this solution, use CKF.

janekpc wrote:

The miniature circuit breaker is mainly used for short-circuit protection. It does not disconnect the circuit because it is its characteristics that it withstands several times higher currents for a short period of time

Thank you for the whole answer but I was not talking about the miniature circuit breaker, but the motor circuit breaker. By the way, if I have an overcurrent breaker, for example A6? and connect to it a motor that will start drawing 7A at start-up, will it disconnect my circuit after a while (the overcurrent switch has a time delay?)? Did you mean motor circuit breaker by the overcurrent breaker?
And I still don't quite understand the operation of the '' phase failure sensor '' could you send a schematic?

-The circuit breaker is the so-called S-ka or automatic fuse if you prefer. In general, you should also protect the motor against short circuits so that the failure of one motor does not crash the entire main switchboard.
- On the other hand, the motor switch is a thermal switch with a power switch, because the thermal switch only controls the contactor to disconnect it, and in a motor switch it breaks out, it also disconnects the power supply itself, so if you have a motor switch, you do not need a thermal switch because it is already integrated in the switch.
- The phase loss sensor has the additional advantage that you will not turn on the motor even for a moment in the absence of any phase. See diagrams.

janekpc wrote:

Main

by protecting the motor, do you mean a motor circuit breaker or a thermostat?

From what I read, I understand that a thermic needs a contactor, so a thermic + a contactor = a motor switch? Why, then, is a thermal thermostat used once and a motor protection switch used once?
And today I was dealing with a motor breaker and the next question came to me ... At the motor breaker I had a scale with a knob from 1 to 2.5 I understand that this is the rated motor current? Ie 1 = rated motor current, 2.5 = rated motor current x2.5? If so, how does the circuit breaker know the rated motor current?

Termik plus a contactor does not equal a motor breaker, a motor breaker must also be used contactor here there are no exceptions. The motor switch works not like a contactor but as a disconnector, so you can disconnect the voltage to the motor with it, for example, using the appropriate extension and handle on the front panel of the housing. In this case, we use the motor switch before the contactor and the thermic is always used after the contactor. And the settings on the thermos and motor circuit breakers are usually in amps and do not normally exceed the rated current.

This guide should explain all ambiguities:

https://el12.pl/poradniki/narzedzia-elektryka-70

1.Tzw. termik is strictly overload protection will not work in the event of a short circuit, typical termik does not disconnect the power supply circuit only through bimetals causes disconnection of the auxiliary contacts, which in turn interrupt the contactor circuit by switching off the power supply.
That's why you must use a contactor for a typical thermostat.
2. the motor switch, as the name suggests, also serves to turn the engine on and off because its design causes power interruption.
It also has a suitable contact and housing design allowing it to be switched off under load.
There is no need for contactors in the motor circuit breakers - they can turn the motor on and off locally.
They are often also equipped with a short circuit.

Motor thermals and switches are selected as follows: nominal motor current x 1.1 = thermostat set point.

Sensors of control and asymmetry are used in systems if the device is very sensitive to lack of phase or to asymmetry in the power supply and also to prevent e.g. starting the motor when the driven device has to work only one way.

janekpc wrote:

- The protection against phase loss is made on the basis of the adder and the relay control system, when the voltage at the output of the adder is too low disconnects the relay.

Hello,

It works a little differently. When everything is ok, the voltage from the adder is 0V and when there is asymtria there is some potential in relation to the virtual zero or from the work cable N.