Selection of the machine for loading: expert advice

Automatic switches (automatons) are used to protect against overload and short-circuit currents (short circuit) of electrical equipment connected to them. At short-circuit in the automatic switch the electromagnetic cut-off is provided, from overload currents - thermal protection. The electromagnetic cutoff is triggered instantaneously, thermal protection - over time, based on the value of the overload current (a current whose magnitude exceeds the nominal current of the machine indicated on its housing).

Making the right choice

Often there is a need to connect additional electrical equipment (warm floor, electric pump, etc.) to a separate group (machine). In this case, you need to select the machine for the load. Incorrect calculations can lead to failure of protection in the event of an emergency or frequent disconnection without a 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 the document only indicates the power consumption, 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 by email. Equipment current can be determined with the help of a clamp meter or some other electrical. Measuring instrument, briefly switching on the equipment at full capacity. Now, knowing the value of the current consumption, you can determine the nominal current of the machine. It is selected from the estimated consumption, but in the direction of increase. For example, if it is 20 A, then the machine will be 25 A.

Calculation of the short-circuit current

The choice of the machine for the load involves calculating the short-circuit current . To operate, a criterion of a short-circuit with a certain value is necessary. It takes different values for different automata. Modern devices have in their marking one of the letters: B, C or D. B = 5, C = 10, D = 20. The figure is the coefficient by which to multiply the nominal current of the machine. The resulting value is multiplied by 1.1 (safety factor). As a result, the value at which the machine will work out is output. 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 equipment connection point. Then 220 (voltage level in Volts) is divided by the amount of this resistance, and you get the real short-circuit current. It must be equal to or greater than the short-circuit trip-out value of the machine.

The choice of the machine for loading under the above requirements, as a rule, provides for the normal operation of the device with the appearance of minor overload currents, 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 automaton that already exists? For this, it is necessary to determine the amount of load current consumed (as is done above). It must not exceed the nominal value of the machine.

If you are having trouble, and you can not calculate the machine for the load, we advise you to contact a specialized organization.