Engr.Tech

Icu:  The rated breaking capacity (Icu) or (Icn) is the maximum fault-current a circuit-breaker can successfully interrupt without being damaged. The probability of such a current occurring is extremely low, and in normal circumstances the fault-currents are considerably less than the rated breaking capacity (Icu) of the CB. On the other hand it is important that high currents (of low probability) be interrupted under good conditions, so that the CB is immediately available for reclosure, after the faulty circuit has been repaired. It is for these reasons that a new characteristic (Ics) has been created, expressed as a percentage of Icu, viz: 25, 50, 75, 100% for industrial circuit-breakers.

In part one of this instrumentation and control (I & C) series, we'll go over the fundamental terminology and concepts used when working with industrial plants. This is the first of a series of technical articles about instrumentation and control. In this series, we will discuss the basic concepts and principles that govern the operation of industrial plants. Concepts associated with measurements of flow, level, temperature and pressure, electronics and pneumatics instrumentation, control loops, PID control, and others will be addressed. Article Scope Someone once asked a colleague what his occupation was. He replied without hesitation, "I am an instrumentation and control engineer." "And what is that?" asked his interlocutor. "...Oh. Oh ... I'm in trouble," thought the engineer. To explain what a mechanical, electrical, chemical, or electrical engineer does is relatively easy, but it is another story to concisely describe the work pe