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*Instructions are at the bottom*
This circuit shows the difference between 2 kinds of earthing systems. The "TN" network and the "IT" network.
T = Terre = earth
N = Neutre = neutral
I = Isoler = isolated
TN stands for Terre Neutre.
The TN network is pretty common for electricity distribution. In the electrical substation 3 high voltage phases will be transformed to low voltages (400 V for example). Those 3 phases will be connected in a Y circuit on the secondary side, and the starpoint will be connected to earth (grounded). From this grounded point, the N (Neutral) conductor and the PE (Protective Earth) conductor are delivered to the costumors with 1 or 3 phases.
When a live wire short circuits with a grounded exposed conductive surface, a high current will flow and trips the RCD or circuit breaker.
IT stands for Isoler Terre.
When a high continuity system is required (like a operating room), the starpoint of the transformer isn't grounded, or is grounded with a very high impedance.
When a live wire short circuits with a grounded exposed conductive surface, no current or a very very small current will flow. The system can continue without tripping any circuitbreakers or RCD's. Only when a second live wire or N short circuits with the same grounded exposed conductive surface, a high current will flow due to direct short circuit. To prevent this, a insulation monitoring device is used to monitor the impedance. This device sends a specific signal into the circuit. When everything is correct, resistance >50 kΩ, the signal will barely return to the device. When a live wire, or N short circuits with a grounded exposed conductive surface, the resistance drops below 50 kΩ and the device will send a alarm or it will cut-off the powersupply to the circuit.
How to use:
Both circuits have a transformer which transforms 230 V to 24 V. The top transformer is grounded on secondary side (TN network). The bottom transformer is grounded with high impedance (high resistance IT network).
When turing on the primary circuits, the lamps will burn.
The right switch, is the switch to short circuit the phase to earth. The left one, to short circuit N to earth.
With the top circuit, when closing the right switch a high current will start to flow instantly.
With the bottom circuit, when closing the right switch no current will flow. Only when the left switch is closed, a direct short circuit is created and a high current will flow.
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