08/09/2023
The earthing system types
Five different earthing system types are included in BS 7671: TN-S, TN-C-S, TT, TN-C, and IT.
N = Neutral S = Separate C = Combined T = Earth
I = Separate
The kind of earthing system to use is one of the first things to be decided when planning an electrical installation. Let's review the most prevalent earthing systems:
1. Earthing the TN-S system
The earthing terminal of the consumer is typically attached to the metallic sheath or armor of the distributor's service cable entering the premises in a TN-S system, where the neutral of the energy source is connected to earth at one place only, at or as close to the source as is reasonably practical.
2. Earthing of TN-C-S systems
The supply neutral conductor of a distribution main is linked to the earth at the source and periodically throughout its course in a TN-C-S system. Protective multiple earthing (PME) is the common name for this. In this configuration, earth fault currents generated in the consumer's installation are securely returned to the source through the distributor's neutral conductor. The distributor will offer a consumer's earthing connector that is connected to the incoming neutral conductor in order to achieve this.
3. Earthing of the TT system
In a TT system, the neutral of the energy source is linked like in a TN-S system, but the distributor does not provide a facility for the customer to earth themselves. With TT, the consumer is required to build an appropriate earth electrode close to the installation as their own connection to the ground.
