14 Electric Wiring: Domestic
L
Consumer’s installation
Supply
N
N
E Metal cable sheath Earth electrode General mass of earth (Single-phase shown for clarity) Separate neutral and earth conductors
FIGURE 1.6
TN-S system.
However, the system inside the consumer’s premises continues to have separate (S) earth and neutral conductors (Figure 1.7). L
Consumer’s installation
Supply
Armour of supply cable
N
Link in consumer’s cut-out
N E
Earth electrode General mass of earth (Single-phase shown for clarity) Combined earth and neutral conductor for supply. Separate earth and neutral in consumer’s installation
FIGURE 1.7
TN-C-S system.
These are the three main earthing systems used in the United Kingdom. They all rely on an earthed star point of the supply transformer and various methods of providing an earth path for fault currents.