Automatic switches (automatic devices) are used to protect against overload and short circuit currents (SC) of the electrical equipment connected to them. In case of a short circuit, an electromagnetic cut-off is provided in the circuit breaker, and thermal protection against overload currents. The electromagnetic cutoff works instantly, the thermal protection - after some time, based on the magnitude of the overload current (current, the value of which exceeds the rated current of the machine indicated on its case).
Making the right choice
Often there is a need to connect additional electrical equipment (underfloor heating, electric pump, etc.) to a separate group (automatic). In this case, it is necessary to select the machine according to the load. Incorrect calculations can lead to failure of the protection in an emergency or frequent shutdowns for no reason. The choice of the automatic loader includes the calculation of the current consumption of the connected equipment. This value can be found from the passport data. If only power consumption is indicated in the document, then the current will be equal to the power divided by the voltage level (a simplified formula for a single-phase network). In the absence of documentation on e-mail. equipment current can be determined using current clamps or some other el. measuring device by briefly turning on the equipment at full power. Now, knowing the magnitude of the current consumption, you can determine the rated current of the machine. It is selected from the calculated consumption, but upwards. For example, if it is 20 A, then the machine will be 25 A.
Short circuit current calculation
The choice of the machine according to the load provides for the calculation of the short circuit current. For operation, a short-circuit criterion of a certain magnitude is required. It takes different values for different automata. Modern devices have one of the letters in their marking: B, C or D. B \u003d 5, C \u003d 10, D \u003d 20. The number is the coefficient by which you need to multiply the rated current of the machine. The resulting value is also multiplied by 1.1 (reserve factor). As a result, the value at which the machine will work is displayed. It remains to determine the true value of the short circuit current. To do this, it is necessary to measure the impedance of the "phase-zero" loop to the point of connection of the equipment. Then 220 (voltage level in Volts) is divided by the value of this resistance, and you get the actual short circuit current. It must be equal to or greater than the value of the short-circuit operation of the machine.
The choice of the automatic machine according to the load, subject to the above requirements, as a rule, provides for the normal operation of the device when minor overload currents appear, as well as its operation in the event of an overload caused by a malfunction of the connected equipment.
If the machine is already installed…
How to calculate the load on an existing machine? To do this, it is necessary to determine the amount of consumed load current (how this is done is described above). It should not exceed the nominal value of the machine.
If you have any difficulties and you cannot calculate the machine according to the load, we advise you to contact a specialized organization.
