Circuit breaker withstand ratings and overload conditions

These are two elementary characteristics inherent to any circuit breaker. If you get the trip rating right, but neglect one of these, you’ll be all washed up . . . .

The circuit breaker protects against damage from large instantaneous currents that develop in circuits by avoiding the situations described in a previous article. One of the technical ratings a breaker has is a withstand current rating. Another to be mindful of is an overload condition.

The withstand current rating generally describes a breaker’s ability (in terms of mechanical strength) to withstand the electromagnetic forces generated during a fault without sustaining structural damage that would hinder their protective function. This rating is specified in terms of kilo-amps: 20 kA, 30 kA, etc.

Breakers also protect against situations where the full-load current for some reason becomes larger than designed but smaller than that of a fault current. Overload currents are smaller, and their effects don’t become immediately obvious, but they’ll eventually result in cable and insulation damage if allowed to continue unchecked. Certain kinds of breakers and protective devices can detect this overload condition and break the circuit.

You can read more about these concepts in a free course published by Siemens called “Basics of Circuit Breakers.” Here’s the link: