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In modern electrical and control systems, every action — even the smallest one — must be monitored, recorded, and controlled.
The Auxiliary Switch is a smart yet simple component designed to tell the system what’s really happening inside the breaker:
whether it is ON, OFF, or has tripped due to a fault.

🔹 What Is an Auxiliary Switch?

An auxiliary switch is an additional electrical contact unit that is electrically isolated from the main power circuit, yet mechanically synchronized with the main contacts of the breaker or magnetic protector.
In simple terms — when the main breaker opens or closes, the auxiliary switch changes its state simultaneously, sending a signal to the control system.

The contacts may be:

  • NO (Normally Open) – closed when the breaker is ON.

  • NC (Normally Closed) – opened when the breaker is ON.

  • Or a combination of both in a single SPDT (changeover) structure.

🔹 Why It Matters

In critical environments — defense, industrial, or medical — there’s no room for guesswork.
A control system or load-management computer must know, in real time, whether a breaker has been activated, tripped, or manually switched off.
The auxiliary switch provides this information reliably, precisely, and instantly.

Key advantages:

  • Remote monitoring and control – allows PLC or SCADA systems to track breaker status in real time.

  • Smart maintenance and alerts – forms the basis for alarms and automated fault diagnostics.

  • Safety integration – enables timed disconnection or prevents unintended restart after a trip.

  • Isolation between power and control circuits – keeps low-voltage control (e.g., 24 VDC) separate from high-voltage power (e.g., 230 VAC).

🔹 Auxiliary Switches in Airpax™ Products

In Airpax™ magnetic circuit breakers, auxiliary switches are an integral part of the design —
offered either as an internal option within the series pole, or as an external control module.

Each contact is engineered for:

  • Simultaneous operation with the main contacts, ensuring accurate status feedback.

  • Complete electrical isolation, allowing mixed-voltage operation.

  • Optimized contact materials – gold or silver, chosen per application:

    • Gold contacts (REG) for very low-voltage signals (below 6 VAC or 5 VDC).

    • Silver contacts for higher loads (up to several hundred mA).

  • Reliable operation both under manual actuation and automatic trip, ensuring accurate event signaling.

For example, in the IAL, LEL, and AP series, Airpax™ auxiliary switches are available with codes such as –IREC4, –IREG4, –IREC5,
and can be configured for any Trip Series arrangement.

🔹 Typical Applications

  • Industrial control panels – monitoring motor protection, frequency converters, and multi-phase power systems.

  • Defense and aerospace systems – feedback to control logic or data logging units.

  • Medical and precision instrumentation – strict supervision of power and safety interlocks.

  • Energy and infrastructure – real-time monitoring of DC/DC converters, power supplies, and UPS units.

  • Industrial IoT – acting as a “status sensor” transmitting real-time data for remote analysis.

🔹 Simple Integration – Major Impact

Though small, the auxiliary switch directly enhances:

  • Operational reliability,

  • Reduced downtime, and

  • Predictive maintenance capability.

Airpax™ switches are built to withstand the harshest environments —
shock levels up to 100 G, vibration up to 2000 Hz, and insulation performance meeting UL1077, VDE, and MIL-PRF-39019 standards.
The hydro-magnetic design of the AP and IAL series ensures stable operation under extreme temperatures and vibration conditions.

🔹 Amironic – Official Airpax™ Representative in Israel

Amironic Ltd. proudly represents Sensata-Airpax™ in Israel — one of the world’s leading manufacturers of rugged magnetic circuit protection solutions.
With a broad range of products — from auxiliary switches to precision current protection and three-phase breakers —
Amironic provides reliable, compliant, and easily integrated solutions tailored for every Israeli application.

⚙️ In Summary

The auxiliary switch may be small, but it’s the intelligent sensor that lets your system “see” what’s happening behind the panel.
With Airpax™ engineering and Amironic’s local expertise, these switches deliver dependable monitoring and control —
ensuring operational continuity in every environment, under every condition, and at every engineering standard.

Signal Logic
Control System Integration
Indication vs Safety
Common Engineering Mistakes
How to Specify the AUX Option
FAQ
Signal Logic

The Airpax auxiliary switch does not sense current.
It reflects the mechanical state of the circuit breaker.

The contact changes state when:

  • The handle is moved to OFF

  • The breaker trips due to overcurrent or fault

  • The breaker is reset to ON

In other words, the auxiliary contact reports:
“Is this breaker currently allowing power to flow?”

This makes it a true status feedback signal rather than an electrical measurement.

Control System Integration

The auxiliary switch creates a digital interface between the power breaker and the control system.

Typical uses include:

  • PLC or controller input

  • Vehicle power management systems

  • BMS or energy control units

  • Alarm or indication panels

  • SCADA and monitoring systems

Using the auxiliary contact, the system can:

  • Detect a tripped breaker

  • Lock out equipment until reset

  • Generate alarms

  • Log protection events

  • Trigger automatic recovery logic

This turns the circuit breaker into an intelligent system component.

Indication vs Safety

An auxiliary contact is for indication and control, not for safety.

It is designed to:

  • Report breaker state

  • Provide a logic signal

It is not designed to:

  • Carry load current

  • Interrupt power

  • Act as a safety-rated device

If the contact is required for a safety loop, SIL function, or emergency shutdown, a dedicated safety device must be used.

Common Engineering Mistakes

Typical integration errors include:

  • Using the auxiliary contact to drive a relay or load

  • Assuming it measures current

  • Confusing handle position with trip indication

  • Selecting NO when a fail-safe NC is required

  • Ignoring electrical noise and contact rating

The auxiliary switch must be treated as a control signal, not a power contact.

How to Specify the AUX Option

When ordering an Airpax breaker with an auxiliary switch, the following must be defined:

  • Contact type: NO, NC or SPDT

  • Switching logic: how the contact changes when the breaker trips

  • Number of contacts

  • Intended use: indication only or control input

The AUX configuration is encoded in the breaker part number.
An incorrect selection will cause the system to receive the wrong logic state.

For this reason, the AUX option should always be specified based on system logic, not just on catalog terminology.

FAQ

Does the auxiliary switch sense current?
No. It only reflects the mechanical state of the breaker.

Does it change when the breaker trips and when it is turned off manually?
Yes. In both cases the contact changes, indicating that the breaker is no longer allowing power flow.

Can it be used to drive a relay or load?
No. It is for signal-level indication only.

Should I choose Normally Open or Normally Closed?
In most control systems NC is preferred, as it provides a fail-safe signal if a wire breaks.

Is the auxiliary switch suitable for military and industrial environments?
Yes, for signaling purposes. It is designed to operate in the same environments as the breaker itself, but it is not a safety-rated device.

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