ACB Working – Air Circuit breakers generally have two pairs of contacts. The main pair of contacts (1) carries the current at normal load and these contacts are made of copper metal. The second pair is the arcing contact (2) and is made of carbon. When the circuit breaker is being opened, the main contacts open first. When the main contacts open the arcing contacts are still in touch with each other. As the current gets a parallel low resistive path through the arcing contact. During the opening of main contacts, there will not be any arcing in the main contact. The arcing is only initiated when finally the arcing contacts are separated. Each of the arc contacts is fitted with an arc runner which helps. The arc discharge moves upward due to both thermal and electromagnetic effects as shown in the figure. As the arc is driven upward it enters the arc chute, consisting of splatters. The arc in the chute will become colder, lengthen, and split hence arc voltage becomes much larger than the system voltage at the time of operation of the air circuit breaker, and therefore the arc is extinguished finally during the current zero. The air brake circuit box is made of insulating and fireproof material and it is divided into different sections by the barriers of the same material, as shown above, figure (a). At the bottom of each barrier is a small metal conducting element between one side of the barrier and the other. When the arc, driven upwards by the electromagnetic forces, enters the bottom of the chute, it is split into many sections by the barriers, but each metal piece ensures electrical continuity between the arcs in each section, the several arcs are consequently in the series.