Circuit breaker failures have a serious potential for harm, both to people and to equipment.

Circuit breakers are a known technology, and companies should have good knowledge of how to prevent failures. Unfortunately, we observe that companies do not sufficiently learn from previous incidents.

What is a circuit breaker?

A circuit breaker is a switch that should be dimensioned to conduct, break or close the current path both in normal operation and at defined fault currents. Operation of the breaker can be performed directly on the circuit breaker itself or remotely, from a central control room, for example.

The main purpose of a circuit breaker is to protect cables and equipment from overloads, short circuits and ground faults. It can also act as a disconnect or separation function to order to deenergise parts of a system.

Serious incidents

In recent years, circuit breakers have been involved in a number of serious incidents in the petroleum industry.

Havtil has investigated some of these incidents:

High power and high current

Circuit breakers are often used where high power and high current are present. When the current path is interrupted, powerful electric arcs can occur. Circuit breakers are designed to interrupt the current safely by handling and extinguishing any arcs. Gas or air is most often used to prevent or handle arcing when the breaker opens.

There are several types of circuit breaker available from different suppliers and for different applications and voltage levels. Some circuit breakers are replaceable while others are a permanent part of a panel. Circuit breakers in use today are commonly mechanical devices with many moving parts.

Underlying causes

Through our investigations and experiences from other supervisory activities, we see that incidents involving circuit breakers share a number of features.

Underlying causes often concern:

  • Aging and residual life assessments (non-establishment of service life requirements)
  • Technical weaknesses in design
    • Misdimensioning
    • Frequent start/stop of equipment with large starting currents
    • Missing barriers in the event of failure
  • Weaknesses in maintenance and verifications (unable to detect all failure modes or developing failure modes)
  • Failure to implement risk-mitigation measures to reduce the likelihood and consequences of an arcing incident
  • Lack of learning from similar events
  • Deficient planning and performance of work

Havtil follows up

Havtil has a clear expectation that the companies will use experience from previous incidents involving circuit breakers in their improvement work, and we will follow up the companies' work on this in our future supervisory activities.

We will also contribute to knowledge sharing through conferences and seminars.

In 2025, Havtil is also planning its own electrical safety seminar, whose topics will include incidents involving circuit breakers. More information about the electrical safety seminar will be available in due course.