Miniature and Moulded Case Circuit Breakers

Closing a circuit breaker after a trip can have devastating effects and result in serious injuries.

If the automatic operation of a circuit breaker was caused by an overload rather than a short-circuit fault, the circuit breaker can generally be reclosed once the cause of the overload has been remedied. However, one manufacturer quotes that their circuit breaker is rated for 50 operations at 6 times the rated current whilst specifying the circuit breaker can operate 6,000 times at rated current and another 4,000 times without current.

A trip with a large overload or short-circuit current will result in damage to the contacts and arc shutes within the circuit breaker. Miniature and moulded case circuit breakers are generally designed for one trip at their ultimate short-circuit rating but some may specify 3 trips at rated short circuit current.

It will pay to understand the short-circuit ratings of site circuit breakers, fault levels at the site and the duty that the circuit breakers receive through their life. Having a maintenance procedure in place for protection equipment is important to prevent incidents.

Miniature circuit breakers should never vent out around the operating handle/lever but moulded case breakers may. One manufacturer states “If the operating handle and/or arc gas vents is contaminated heavily with soot and molten metal particles, replace the breaker immediately.” A handle can be permanently mounted on moulded case breakers to help protect the operators hand should venting occur around the normal handle/lever. Breakers mounted inside panels with an extension and handle to the outside of the panel should not burn the operators hand as any venting around the normal handle/lever will be inside the panel.

All circuit breakers, including LV ACBs and HV circuit breakers, will need to be maintained or replaced. Check the specifications and design standard for the circuit breakers at your sites and follow all manufacturer recommendations for maintenance and replacement.

More Blog Articles

Poletop Fires

Western Power was recently plagued with approximately 70 poletop fires that caused widespread outages and damage to the network. Around 47,000 homes and businesses were

Read More »