Personal protection

In the event of an earth fault in your own or someone else's electrical system, the fault is connected to earth. Between the drain pipe and the earth electrode there is an unknown earth resistance. In unfortunate circumstances, the earth fault current can travel towards the drain pipe, and follow the conductive coating up the drain pipe. When you take a shower, there will be a voltage on the drain, and when you turn on the water, the body becomes part of the earth fault current circuit. The return route goes via the water pipe down to the main ground rail, and down into the soil again.

Tjoememuffe uten

Illustration 1: IT network without Tjømemuffe. Ill.: Trainor AS

In an IT network with 230 V, the voltage is reduced to 132 V when it goes to earth. However, in the event of an earth fault, one or more in the transformer circuit, the voltage can be much higher. This voltage will be distributed across the resistors that are in series in the circuit where the earth current flows. In such cases, the voltage across the body can reach well over 50 V. Current flow of this magnitude can be life-threatening.

In the case of installations with Tjømemuffe, there will not be a voltage rise to earth since the drain pipe and the water pipe will have the same potential and there will be no potential differences.

Tjoememuffe med

In facilities with an IT network where there should have been a Tjømemuffe but this is missing, there are several methods to solve the equalization of the drain grate.

Tjoememuffe med

Illustration 2: IT network with Tjømemuffe. Ill.: Trainor AS