Earthing Types
Earthing Types
BS 7671 lists five types of earthing system:
- TN-S
- TN-C-S
- TT
- TN-C
- IT
Where those letters indicate:
- T = Earth (from the French word Terre)
- N = Neutral
- S = Separate
- C = Combined
- I = Isolated
An explanation can be found here.
A useful IEE document on earthing (presumably most DIYers can ignore the section on earthing caravan pitches)
You can find details on installing a TT earth here.
Earthing types explained
TN-S
Earth connection provided by the supplier.
TN-C-S
Also known as PME, this earth connection is also provided by the supplier. Its direct connection to the neutral brings some added issues that require addressing at the consumer's end.
TT
Local earth connection, either to an earth rod, or in years past to a metal water pipe. TT installs have long required whole house RCD or ELCB protection
TN-C
IT
Never used for permanent house supplies, this is commonly used for portable generators. Simply there is no reliable earth connection on the system.