Automatic switches (automatic machines) are used to protect against overload and short circuit currents (short circuit) of electrical equipment connected to them. With a short circuit, the circuit breaker has an electromagnetic cut-off, thermal overload protection against overload currents. The electromagnetic cut-off is triggered instantly, thermal protection - after some time, based on the magnitude of the overload current (a current whose value 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 (floor heating, electric pump, etc.) to a separate group (automatic machine). In this case, the choice of the machine according to the load is necessary. Incorrect calculations can lead to failure of the protection in the event of an emergency or frequent shutdown for no reason. The choice of the machine for the load 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 (simplified formula for a single-phase network). In the absence of documentation on e-mail equipment current can be determined using clamp meters or some other electronic. 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 estimated consumption, but upward. For example, if it is 20 A, then the machine will be at 25 A.
Short circuit current calculation
The choice of the machine according to the load provides for the calculation of the short circuit current. To operate, a short-circuit criterion of a certain value is required. For different machines, it takes different values. Modern devices have one of the letters in their markings: B, C or D. B = 5, C = 10, D = 20. The number is the coefficient by which the rated current of the machine must be multiplied. The resulting value is still multiplied by 1.1 (safety 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. For this, it is necessary to measure the value of the impedance of the phase-zero loop to the point of equipment connection. Then 220 (voltage level in Volts) is divided by the value of this resistance, and you get a real short-circuit current. It must be equal to or greater than the value of the operation of the machine on a short circuit.
The choice of the 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 during overload caused by a malfunction of the connected equipment.
If the machine is already installed ...
How to calculate the load on an existing machine? For this, it is necessary to determine the magnitude of the consumed load current (as is done - described above). It must not exceed the rated value of the machine.
If you have any difficulties, and you cannot calculate the machine for the load, we advise you to contact a specialized organization.