TN-S System
- underground cable
- earth comes into the building the same way as the phase and neutral
TT System
A TT system has the neutral running in the supply cable(s) as normal, and the earth from the installation is connected to an appropriate Earth Electrode inserted into the ground. An RCD is essential in an installation formed by a TT earthing arrangement.
- via two overhead conductors
TN-C-S System
A TN-C-S system has the neutral and earth COMBINED in the Electricity Boards supply cable(s), and SEPARATE with-in the installation, (this being the meter position and onwards).
