N2 Electrical Trade Theory|The Easy Way! 41


Silver tungsten maintains its form even aſter the melting temperature of the silver is exceeded. Silver tungsten can withstand very high temperatures such as those generated by the arc which is formed when the circuit-breaker trips under overload and short-circuit conditions.


2.7.12 Interpole barriers


Tere are interpole barriers between the poles of three-phase circuit-breakers to ensure that the arc does not jump from one phase to another.


2.7.13 Ambient temperature


Ambient (surrounding) temperature can have a significant effect on the accuracy of circuit-breakers and steps are usually taken to reduce the effects as much as possible. Termal magnetic circuit-breakers


When the ambient temperature is very low, the tripping current as well as the time delay is increased, fig. 2.10. On the other hand, when the ambient temperature is very high, the overcurrent tripping value as well as the time delay is reduced.


Magnetic circuit-breakers


Te viscosity of the oil used in the cylinder of the hydraulic time delay device is affected by the ambient temperature. When the ambient temperature is very low, the oil becomes thicker and the time delay increases. On the other hand, when the ambient temperature is very high, the oil is thinner and the time delay is reduced.


▲ 3.13 A circuit-breaker is a mechanical switching device which can operate as a manual switch and its purpose is to automatically disconnect an appliance or circuit from the supply in the event of an abnormal condition such as an overcurrent.


▲ 6.8.1 A circuit-breaker may be used as a main or local switch-disconnector provided that it complies with the standards for a switch-disconnector, or alternatively, a switch-disconnector must be connected on the supply side of the circuit-breaker.


▲ 6.6.1.20 Unless obvious, permanent labelling shall identify all incoming and outgoing circuits of the distribution board.


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