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.

Power Quality Problems

The most common types of Power Quality problems are presented in the following Table

Power quality

What is Power Quality?

1. The concept of powering and grounding sensitive equipment in a manner that is suitable to the operation of that equipment.”
2. “Within the industry, alternate definitions or interpretations of power quality have been used, reflecting different points of view.”
3. The definition of Power Quality cannot be limited to the characteristics of the supply power. The definition must also include the requirements of the load.“

Power Quality Solution Strategy

1. good grounding system 
2. Harmonic solutions
3. Surge solution 
4. Voltage variation solution 

Grounding Codes and Standards

 Ideally a ground should be of zero ohms resistance. The NEC has stated that "A single electrode consisting of a rod, pipe, or plate which does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode..." Once you have added the supplemental ground you have met the requirement for the NEC.

This does not mean that the value of the ground now has to be 25 ohms or less. The ground resistance values objectives vary from industry to industry.

Telecommunications industry has often used 5 ohms or less as their value for grounding and bonding. The goal in ground resistance values is to achieve the lowest ground resistance value possible that makes sense economically and physically

The need to ground

There are important reasons why a grounding system should be installed.

1- The most important reason is to protect people

2- Protection of structures and equipment from unintentional contact with live conductors


3- Ensure maximum safety from electrical system faults and lightning.