How Does a Shunt Trip Breaker Work?

I get this question a lot from people starting their apprenticeship journey. Every type of circuit breaker has its own function. Shunt trip breakers fall into that category and are predominantly used in kitchens and other spaces that might have electrical hazards.

Generally, shunt trip breakers work in these ways:

  • Manually, with a switch
  • Automatically, with an external power source.

They send a signal to the main circuit breaker’s electromagnet in both cases. The electromagnet gets charged by a power surge transmitted by the shunt trip breaker, and it trips the main circuit breaker.

I’ll go into more detail below.

A Few Words About the Electrical Circuit System Before We Start

A building’s electrical system consists of small circuits that connect to a power source.

Each circuit “arrives” at the main panel that consists of cables and circuit breakers. The reason is that, ultimately, those circuits do not connect to each other. Thus, when one circuit is damaged or undergoes a power surge (i.e., the kitchen’s circuit in a home), all the other rooms’ circuits remain unaffected by the issue.

The circuit breakers exist to cut the power when a power surge occurs. They connect to the electrical system and individually to an electromagnet and a switch.

The breaker’s electromagnet gets charged and overheats when excessive electricity runs through the electrical system. At that moment, the switch immediately trips, forcing the circuit breaker also to trip.

Each circuit is connected in series, while all circuits are connected to the power source in parallel formation.

What Do We Call a Shunt Trip Breaker?

hand holding a shunt trip breaker accessory
Video | Schematix

A shunt trip breaker is an optional accessory that allows the main circuit breaker to trip by remote signaling.

The shunt trip breaker consists of two conductive elements, between which there is a metal strap. The metal is constructed with manganese, nickel, and copper. One end is connected to the ground, and the other connects to the control system.

The device is resistive and placed in series on a Direct Current (DC) line. However, the resistance levels are low enough not to disrupt the electricity flow through the circuit system.

One can measure the amperage that flows through the system by using the voltage and the resistance of the shunt (Ohm’s law, Amperage=Volts/Resistance).

The shunt trip breaker can also connect to other devices, such as PLCs and current monitoring devices. Those devices give off certain effects depending on the levels of current that pass through the system.

In general terms, these breakers are used for manually shutting off the electrical system in case of emergencies or with a sensor.

What Does a Shunt Trip Breaker Do?

Shunt trip breakers are mainly used for remote tripping of main circuit breakers.

Most of the time, the shunt trip breaker is connected to a control panel that connects to an emergency system (i.e., a fire system). They are usually tied to chemical suppression systems that send remote signals to the system so they can cut off the electricity.

The shunt trip breaker has thermomagnetic elements within its construction, which do not trip because of the amount of current flowing through it.

Why is a Shunt Trip Breaker Important?

shunt trip breaker in zoom
Video | Electrician U

Shunt trip breakers are mostly used to cut the flow of electricity into a building’s system.

The most common usage of this type of breaker is fire prevention. For the shunt trip breaker to work, in this case, the smoke detector needs to turn on. The operation of the alarm triggers the shunt trip breaker, which prevents all electrical hazards.

The importance of the breaker lies in the possibility of electrocution. For example, if a smoke detector is connected to a sprinkler, it shuts off the electrical system. This action reduces all electrocution risks to a minimum.

The feature that adds to its biggest value add is the manual switch. That switch allows a user to shut off the main circuit breaker to minimize danger in emergencies.

The shunt breaker also prevents damage to the building’s electrical equipment.

Where Can You Use a Shunt Trip Breaker?

shunt trip breaker panel diagram
Video | CASService

In general cases, the shunt trip breaker is not required in most electrical circuit systems.

However, they are usually mandatory on the:

  • Kitchens
  • Offices
  • Elevators

Shunt trip breakers in kitchens and offices are mainly used for fire-related emergencies. As stated above, once the fire detector starts to operate, the shunt trip breaker trips the main circuit breaker to prevent damage to a building’s electrical systems.

Elevator shunt trip breakers also have to do with fire detection.In this case, all such breakers’ purpose is to cut the power before the sprinkler systems’ operation, not just to protect the main circuit.

Aside from the above cases, shunt trip breakers are ideal for areas where heavy and industrial machinery is used.

How Does a Shunt Trip Breaker Work?

The shunt trip breaker is always connected in series with other circuit breakers.

Since the shunt trip breaker has very little resistance, electricity flows through its metallic strip without affecting the circuit. Under normal conditions, you can use the shunt trip to measure the current passing through.

An electromagnet is located under the circuit breaker’s switch so it can trip during a power surge. A shunt trip breaker can aid a circuit breaker tripping through two methods:

  • By using an external power source
  • By functioning via a remote switch

Both cases allow the shunt trip breaker to send a signal to trip the main breaker in the electrical system.

1. External Power Source

shunt trip breaker in an elevator controller system
Video | Joe Klochan

The external power source is used for elevator and kitchen circuit breakers.

They receive a signal from an external system (i.e., the activation of the fire alarm) that is transferred from the shunt trip to the main breaker. That signal is the charging of the electromagnet of the circuit breaker, which then trips the switch.

During a power surge, the circuit breaker can trip on its own, nevertheless, the shunt trip breaker acts as a safety mechanism in case the tripping doesn’t happen.

2. Remote Switch

The remote switch is usually placed outside a building.

To activate the shunt trip breaker manually, one needs to access the switch. It is usually equipped with a button that transmits an electrical surge through the wiring. Thus, the power is cut off.

Remote switches are mainly used as a safety precaution.

Take a look at some of our related articles below.




Video References

Electrician U

Schematix

CASService

Joe Klochan

Jr Electric School

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About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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