What is the function of auxiliary switch in circuit breaker?
The auxiliary switch provides a secondary contact that signals the breaker's status to other equipment, without carrying the main load current. It is typically used for remote indication, interlocking, and control logic based on whether the breaker is open or closed.
What exactly is an auxiliary switch?
In a circuit breaker assembly, the auxiliary switch is a mechanical contact that moves as the breaker contacts move. It is electrically separate from the main current path and is specifically designed for signaling and control purposes, not for switching the main load. The auxiliary contacts report the breaker's position to other devices or systems such as alarms, controllers, or interlocks.
Key characteristics
Auxiliary switches are typically low-current signaling contacts. They come in configurations that either indicate the breaker is closed, open, or both, and are used to feed control logic or status indicators rather than to bear the main circuit current.
Signal configurations
Common auxiliary contact configurations offer different signaling options to suit control logic and interlock schemes.
- Normally Open (NO): closes when the breaker is closed, providing a "closed" indication to a control circuit.
- Normally Closed (NC): opens when the breaker is closed, providing an inverse signal for certain control schemes.
- Dual (NO + NC): both contacts operate, giving two independent signals for redundancy or more complex interlock logic.
These signals are typically wired to PLCs, annunciators, SCADA systems, or interlock circuits and are intended to carry only signaling currents, not main-load currents.
Typical uses in control systems
Before listing common applications, it is helpful to note that the auxiliary switch acts as a status feedback mechanism, enabling safer and more automated operation of electrical systems.
- Remote status indication for operators and dashboards, so personnel can see whether a feeder is energized.
- Interlocking with other equipment to prevent unsafe or improper sequencing in a system.
- Safety-related signaling that informs control logic to disable or enable certain functions when the breaker is open or closed.
- Feed for control circuits that require a known safe state before downstream equipment operates.
In all cases, auxiliary contacts handle signaling currents and are not intended to interrupt high-power loads. Their ratings are specified by the breaker manufacturer and must be matched to the control circuit requirements.
Practical considerations
Before selecting and wiring an auxiliary switch, it is important to consider how the signaling will be used and how it will interact with other safety and automation layers.
- Electrical rating and contact type: verify whether NO, NC, or both are available, along with current/voltage ratings for signaling use.
- Wiring and compatibility: ensure the signaling circuit voltage and logic levels match the control system (PLC/SCADA) and use appropriate input protection if needed.
- Safety and interlocks: design interlock logic to prevent misleading signals that could compromise safety or operations.
- Maintenance and testing: regularly test auxiliary contacts as part of protection-system verification to ensure signaling remains accurate after switch events.
When properly implemented, auxiliary switches enhance monitoring, safety interlocks, and automation without risking the integrity of the main power path.
Summary
Auxiliary switches in circuit breakers provide a secondary, low-current signaling path that reflects the breaker’s position (open or closed). They enable remote status indication, interlocks, and control logic, while ensuring the main load path remains unaffected. Understanding their configurations, ratings, and wiring is essential for reliable, safe electrical automation.
What is the purpose of the auxiliary switch?
Auxiliary switches are used to control and monitor accessories, providing a way to power add-on devices or get information about the status of electrical systems like circuit breakers and motor starters. In vehicles, they allow users to easily power accessories like lights or winches, while in industrial settings, they monitor the position of equipment or trigger alarms based on a circuit's status.
In vehicles
- Powering accessories: They provide pre-wired and fused power for add-on devices like winches, fog lights, and other electrical equipment, so you don't have to add your own aftermarket wiring.
- Control: They give you direct control over these accessories, and some systems, like the "upfitter" switches in a Ford truck, are designed to be easily wired to various devices.
In industrial and electrical applications
- Remote monitoring: In circuit breakers, auxiliary switches provide remote feedback on the breaker's status (open or closed), which helps operators monitor the system from a distance and identify any issues.
- Status indication: They can activate indicator lights or alarms based on the state of a main circuit or piece of equipment.
- Control of secondary functions: In motor control, they can be used to operate other devices, such as a cooling fan, when the motor is running.
How they work
- Vehicle examples: The switches are typically linked to a power distribution box, which then routes power to various locations in the vehicle. When a switch is activated, it completes a circuit and provides power to whatever is wired to it. For safety, it's often recommended to leave the engine running to maintain the battery charge when using high-draw accessories.
- Circuit breaker examples: An auxiliary switch's contacts are mechanically linked to the main contacts of the circuit breaker. When the breaker is opened or closed, the auxiliary switch changes state, which can be used to signal the change to another system.
What is the function of an auxiliary switch in a circuit breaker?
Circuit Breakers: In circuit breakers, auxiliary switches are used to indicate the position of the breaker (open or closed). They can trigger alarms or indicators on a control panel.
What is the purpose of an auxiliary switch on a contactor?
An auxiliary contactor allows one switch to control another (usually larger) switch. The auxiliary contactor has a coil with high-power contacts inside and two sets of low current contacts on either end. The “low voltage” set of contacts is usually labeled as such.
What is the difference between auxiliary switch and alarm switch?
The alarm switch contacts only change state when the circuit breaker trips, not when the breaker is simply turned off. The auxiliary switch contacts change state any time the breaker contacts change state, regardless of how it is done.
