The phenomenon of "current leakage" in electrical engineering is understood as the flow of current through circuits not intended for this. Usually, they are gas and water pipes, instrument casings and other metal structures. When touching them, a person himself becomes part of such a circuit and receives an electric shock of various strengths. Figure 1 demonstrates this effect schematically.
The threshold for leakage at which measures must be taken to reduce leakage is 10 mA. A 30-milliampere leak is already becoming potentially dangerous to humans.
The reason for the appearance of a leak is a violation of the integrity of the standard insulating covers as a result of mechanical damage or normal aging.
Leak detection
The presence of a leak is determined indirectly. It is assumed that with proper insulation, there can be no leakage.
Most accurately, the presence of a leak is detected using a megohmmeter, which measures the value of the insulation resistance. This device is considered a professional one, it is quite rare and therefore in a domestic environment it is replaced with an ordinary tester or indicator.
The procedure for determining the integrity of insulation by a tester is reduced to performing the following operations:
- the device under test (washing machine, electric stove, etc.) must be de-energized (disconnected from the network);
- the tester is switched to the 2 megohm range;
- the tester probes touch the pins of the power plug and the device body.
If the tester shows a finite resistance, then this is considered a sign of an unacceptably high leakage current.
The presence of a leakage current by the indicator is checked by touching a metal surface with its sting. Even a weak lightning of the indicator indicates the presence of a leakage current.
Finding a leak
The specific place of leakage with free access to conductive elements is usually found by visual inspection and finding damaged insulation. In the case of hidden wiring, its identification without special equipment is difficult.
Leakage current protection
The most effective means of protection against leakage current is the use of a differential circuit breaker, which is installed in the electrical panel. The body of such an element has slots for mounting on a DIN rail, and the form factor corresponds to conventional machines, which is clearly seen from the example in Figure 2. The latter allows you to form an intuitive line of devices for managing home electrical wiring.
Quite popular are multi-level RCD circuits, which are assembled by analogy with the input and distribution machines. In this situation, there is a general RCD with a trip threshold of 300 mA, as well as separate RCDs for a particular room, which are designed for a lower leakage current. An example of such a structure, implemented on standard components, is shown in Figure 3.