Summary of the earth connection diagram SLT

The ground connection diagram defines the grounding method of the neutral point of a distribution transformer and of the masses on the user side to ensure the protection of persons and equipment against insulation defects.

We find 5 different neutral regimes namely:

Insulated

Resistor grounding

Grounding by low reactance

Earthing by compensation reactance (due to the capacitive effect of HV lines)

Direct grounding (not used on European networks)

A grounding pattern is characterized by two letters. The first indicates the connection of the neutral of the transformer, it can be:

T for grounded

I for insulated (or impedant) with respect to earth.

The second letter indicates how to connect the user masses, it can be:

T for grounded

N for connection to the neutral, which is connected to earth.

Earth connection diagram TT

This connection is used by ONE for public low voltage distribution

The neutral of the transformer is earthed via a resistor grounding conductor Rn

All the masses of the equipment protected by a single protective device must be interconnected and connected by a protective conductor called PF to a ground connection

TN-C ground connection diagram