What is a circuit breaker?

A circuit breaker is an apparatus in electrical systems that have the capability to, in the shortest possible time, switch from being an ideal conductor to an ideal insulator and vice versa. Circuit breakers requires to reduce arcing ie, Sparks jump for several inches in the highly ionized ambient atmosphere

TN-S system earthing

A TN-S system, shown in fig, has the neutral of the source of energy connected with earth at one point only, at or as near as is reasonably practicable to the source, and the consumer’s earthing terminal is typically connected to the metallic sheath or armored of the distributor’s service cable into the premises.

Type of earthing systems

BS 7671 lists five types of earthing system: TN-S, TN-C-S, TT, TN-C, and IT.

T          = Earth (from the French word Terre)

N         = Neutral

S          = Separate

C         = Combined

I           = Isolated (The source of an IT system is either connected to earth through a deliberately introduced earthing impedance or is isolated from Earth. All exposed-conductive-parts of an installation are connected to an earth electrode.)

When designing an electrical installation, one of the first things to determine is the type of earthing system. The distributor will be able to provide this information. The system will either be TN-S, TN-C-S (PME) or TT for a low voltage supply given in accordance with the Electricity Safety, Quality and Continuity Regulations 2002. This is because TN-C requires an exemption from the Electricity Safety, Quality and Continuity Regulations, and an IT system is not permitted for a low voltage public supply in the UK because the source is not directly earthed. Therefore TN-C and IT systems are both very uncommon in the UK.