REVERSE CURRENT PROTECTIONThe vast majority of household electrical appliances aren’t grounded. At first glance, it is not necessary: the chassis devices are securely isolated from the network, and work with them, usually in dry areas with non-conducting floors. But to rely entirely on technique impossible. If the breakdown or damage to insulation — faulty device becomes a source of serious danger. Fuses are useless: they will not burn out until there is a short circuit.

To avoid electric shock will help you an automatic device that will shut off the appliance from the network, only on the body voltage will be.
The machine is assembled according to the scheme of the trigger with one stable state (Fig. 1). In the case of the circuit “zero” or phases of a network on the body of the appliance rectified voltage through the chain V2, or V3, R1, R2 is supplied to the transistor V4, and it closes. The increased voltage on the collector of the transistor V5 opens relay K1, their contacts K1.1 is locked, and To 1.2 disables the appliance from the mains.
The half-wave rectifier to supply the protective device is assembled to the diode V1. Using the variable resistor R3 sets the trigger threshold of the trigger capacitor C1 eliminates vibration of the contact plates of the relay K1.
In standby, the machine almost does not consume current.
Fig. 1. Schematic diagram of the protective tripping device.
Fig. 1. Schematic diagram of the protective tripping device.
МП26Б transistors can be replaced by МП41, МП42, МП21, МП25, the diodes can be of any type, for a voltage not below 100 V and current of 0.1 A.
Fixed resistors — ULM, ML T-0,25, R7 — wire resistance 8-10 Ohms; variable resistor RZ — SP-01. Capacitors: C1 — MBM 160, C2 —C50.
K1—relay RES-22 (passport RF4.500.129) or mku-48 24 V. the latter is necessary is to loosen the spring anchor.
To protect powerful appliances, you must install the magnetic contactor, designed for a respective load.
T1 — transformer TVK-70/110 from TVs. The voltage at the secondary winding 12 to 20, power 3-5 watts.
Wiring diagram of the automatic device shown PA figure 2.
Fig. 2. Wiring diagram of the machine.
Fig. 2. Wiring diagram of the machine.
Fig. 3. Connection scheme of the device with the appliance.
Fig. 3. Connection scheme of the device with the appliance.
After checking the correct mounting of the diodes V2, VЗ and a common wire (“+”) serves AC voltage of 35-40 V and using the trimmer resistor RZ to achieve that relay K1 is working. Then the appliance is connected to a protective machine and include it in the network (Fig. 3).
When working together with overall electrical appliances (fridge, washing machine) protective device is recommended to be set inside of the body to any place.

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