Circuit breaker repair

Anyone involved in electrical maintenance will most likely need to interact with circuit breakers at some point in their career. Circuit breakers are essential components in electrical systems, designed to protect circuits and people from overload or short-circuit conditions by interrupting the flow of current. While their primary function is to ensure electrical safety, circuit breakers themselves can present hazards due to stored energy. Working with circuit breakers involves managing stored energy hazards, which pose risks to personnel and equipment if not controlled.

There are some types of circuit breakers that, by their design, shield personnel from almost all stored energy hazards. These are usually molded case circuit breakers, which contain all moving components inside a sealed case. This is also true for insulated case circuit breakers —  unless the covers are removed for inspection or service. Both of these types of breakers promote safety by separating personnel from mechanical hazards and direct exposure to energized conductors.

The Dangers of Mechanical Energy

It is important to remember that circuit breakers are mechanical devices that just happen to control the flow of electricity in a circuit. That mechanical energy can be as dangerous as the electrical hazard if the breaker is being serviced. The most common type of stored energy hazard in a circuit breaker is mechanical energy. Understanding how a circuit breaker mechanism works is crucial for comprehending the stored energy hazards associated with it.

At its core, a circuit breaker consists of three main components: the operating mechanism, the trip unit, and the contacts. The operating mechanism is responsible for opening and closing the contacts of the circuit breaker. A typical circuit breaker employs a spring-loaded mechanism, where energy is stored in springs when the contacts are closed and released to open the contacts when a fault occurs. This mechanism ensures rapid interruption of the circuit when necessary to protect against overloads or short circuits.

Closing and Tripping Breakers

There are two areas of stored energy concern when it comes to safety when servicing circuit breakers: energy associated with closing the breaker and energy associated with tripping a breaker.

In the most basic of breakers, there is a single-stage close function. When a breaker handle is mechanically operated in this type of circuit breaker, the parts in the mechanism rotate to transfer this energy to close the circuit breaker contacts. Inside the mechanism there is often a roller that a prop sits against to hold the contacts closed against the spring tension of the contacts. The breaker mechanism holds the contacts closed with sufficient pressure to maintain a low contact resistance to minimize current losses and control heat generation. An example of this type of breaker would be the original Westinghouse DB-25. The rotation of the manual handle was directly related to the speed at which the contacts closed, with full rotation of the handle allowing the prop to fall into place and latch the contacts closed.

As the design of circuit breakers became more complex, the operation of breakers often utilized spring energy on both the closing and opening actions of the breakers. Even the simple DB-25 was improved upon, and a spring-assisted mechanism was added to later models.

Early designs of electrically operated circuit breakers had a single stage close, employing a coil and an armature to rotate the mechanism to that same closed condition. As advances in distribution engineering occurred, the physical operation of breakers changed. Springs were added into the mechanisms of almost every type of circuit breaker. This increased the speed at which the contacts closed, reducing arcing hazards. Many breakers were designed to have two-stage closing mechanisms: charge and then close.

When a circuit breaker is closed, mechanical energy is stored in these springs, ready to be released when the breaker trips. If not properly controlled, the release of this stored energy can cause the breaker to operate unpredictably, potentially leading to injury to personnel or damage to equipment.

Breaker Mechanism Hazards

Based on their design and operation, it is understandable that interacting with breaker mechanisms is not without hazard. When removing covers or parts, such as arc chutes, for service or inspection, it is important to verify that the circuit breaker is tripped, and the mechanism is discharged. Breakers that utilize the charge/close type of operation are equipped with indicating flags that show whether the mechanism is charged or discharged. It is still important to use caution and visually inspect a breaker to verify that it is discharged in case this flag is not operating properly. Once a circuit breaker is tripped and discharged, it can be safely inspected and serviced.

While maintaining a circuit breaker, it will eventually be necessary to close the breaker. If the covers are not in place, make sure to keep fingers clear of any parts that may move during the charging or closing operation of the mechanism. Hazards come from not only the action of the contacts closing, but also from items such as indicating flags, which are located near the front of the breaker, rotate quickly, and may have sharp edges.

Once a circuit breaker is closed, a different set of hazards arise. Breaker contacts open very quickly as a result of the stored spring energy behind the stationary contacts and in the mechanism springs. As the trip function occurs, the contacts fly open, and the mechanism rotates back to its rest position. It is imperative that personnel keep hands and fingers away from all internal parts of the breaker when it is in the closed position, especially if it is not fully assembled. A visual evaluation of the equipment is the only safe activity when the breaker is charged or closed.

As an additional note, use caution when removing breakers from cubicles. Switchgear is designed to have interlocks preventing the racking out of closed breakers from cells, but those interlocks can get damaged or be non-functional due to lack of maintenance. Ensure that breakers are tripped open before any removal occurs. Also be aware that many types of equipment have mechanism discharge functions built into the cubicle so that upon removal, the breaker will automatically discharge. Before interacting with a breaker that has a charge/close type mechanism, ensure that the mechanism is discharged.

Know Your Equipment

Engineering controls have helped to mitigate stored energy hazards by designing circuit breakers with safety features such as interlocks to prevent unsafe operations and mechanisms for safely discharging stored energy, but training and education are still essential for personnel working with circuit breakers. Workers should be familiar with the operation of circuit breakers and understand the risks associated with stored energy. They should receive training on safe work practices, including procedures for isolating and de-energizing circuits before performing maintenance or troubleshooting activities.

Stored energy hazards are a significant concern when working with circuit breakers. Mechanical energy can be stored in circuit breakers, posing risks to personnel and equipment if not properly controlled. By implementing appropriate safety measures, including maintenance procedures, training, engineering controls, and PPE, these hazards can be effectively mitigated to allow for safe maintenance of electrical equipment.

Author Denise Green is the Midwest regional sales manager and national breaker specialist for Group CBS and has been in the electrical distribution industry for 33 years.

Learn more: