📝 Description

Used product
The ABB SACE Isomax S3N 250 is a molded-case circuit breaker for electrical distribution and protection applications in industrial systems and low-voltage switchboards.
The device belongs to the ABB SACE Isomax S3 family and is designed to protect circuits against overloads and short circuits. The version shown in the photographs is configured with 4 poles, a rated uninterrupted current of 250 A, and an operating voltage of up to 690 V AC. The nameplate also indicates compliance with IEC 60947-2 and an impulse withstand voltage Uimp of 8 kV.

⚙️ Main Specifications

• Brand: ABB
• Family: SACE Isomax S3
• Model: S3N 250
• Type: Molded-case circuit breaker
• Number of poles: 4P
• Rated uninterrupted current Iu: 250 A at 40 °C
• Rated operational voltage Ue: up to 690 V AC
• Frequency: 50–60 Hz
• Impulse withstand voltage Uimp: 8 kV
• Standard: IEC 60947-2
• Breaking capacity Icu at 380/415 V: 35 kA
• Utilization category: A
• Protection technology: thermal-magnetic trip unit, depending on configuration
• Construction: SACE Isomax S3 molded-case circuit breaker
• Control: front rotary handle
• Connections: front power terminals visible in the photographs.
  Important Note: ABB documentation provides different S3N 250 configurations with different trip units and settings. The complete ABB code or a specific trip-unit setting that is not clearly legible cannot therefore be assigned from the photographs alone.

🔧 Main Functions

• Protection of electrical lines against overloads.
• Protection against short-circuit currents.
• Circuit interruption under fault conditions.
• Manual line isolation and switching.
• Protection of equipment and conductors in industrial electrical switchboards.
• Possibility of integration with accessories and auxiliary devices provided for the SACE Isomax family.
  ABB documents different configurations of the S3N series with thermal-magnetic and magnetic trip units, as well as different versions and terminals.

🔌 Purpose and Operation

The circuit breaker is installed inside an electrical switchboard to protect a line or power load.
During normal operation, it allows current to flow up to its rated current. In the event of an overload or short-circuit condition, the trip unit operates the opening mechanism, opening the contacts and interrupting the circuit.
The S3N 250 is rated for an uninterrupted current of 250 A at 40 °C. ABB specifies an Icu of 35 kA at 380/415 V for this version.

🧩 Device Configuration

The photographs show:

• ABB SACE circuit breaker body;
• S3 indication on the front;
• rotary control handle;
• circuit-breaker position indicator;
• four poles;
• power terminals;
• trip/protection unit;
• side auxiliary wiring/accessory.
  The presence of the side wiring is simply reported as auxiliary accessory/wiring present, without assigning a specific function that cannot be verified from the photographs.

⚠️ Typical Faults and Symptoms

A circuit breaker of this type may exhibit:

• inability to move the circuit breaker to the ON position;
• immediate tripping upon switching on;
• tripping during an overload;
• failure to open;
• failure to close;
• worn or damaged contacts;
• deteriorated terminals;
• overheating of connections;
• control-mechanism anomalies;
• problems with the trip unit or any auxiliary accessories.
  A circuit-breaker trip does not necessarily mean that the circuit breaker itself is faulty: it may be caused by an overload or short circuit present in the system.

🔍 Diagnosis

Professional inspection may include:

• mechanical check of the control mechanism;
• verification of pole opening and closing;
• terminal inspection;
• insulation testing;
• contact continuity testing;
• trip-unit verification;
• checking of any auxiliary contacts;
• inspection of connection conditions;
• functional testing with appropriate equipment.
  For a complete inspection, the specific configuration of the trip unit and any installed accessories must also be considered.

🛠️ Common Services in Case of Failure

• Circuit-breaker diagnostics.
• Mechanical inspection.
• Cleaning and maintenance.
• Contact inspection.
• Terminal inspection.
• Trip-unit inspection.
• Auxiliary-accessory inspection.
• Replacement of compatible components.
• Functional testing before reinstallation.
• Circuit-breaker refurbishment, where technically possible.

🛠️ Applications

The ABB SACE Isomax S3N 250 is suitable for applications such as:

• industrial electrical switchboards;
• low-voltage electrical distribution;
• protection of three-phase lines with neutral;
• industrial machinery;
• distribution switchboards;
• photovoltaic systems and conversion systems, when provided for by the electrical design;
• protection of loads and lines up to the specified rated current.

💡 Advantages

• High current-handling capability.
• Robust construction for industrial applications.
• Rated current up to 250 A.
• Operating voltage up to 690 V AC.
• Overload and short-circuit protection.
• Compact construction relative to the power handled.
• Wide historical availability of accessories and configurations within the SACE Isomax family.

🛡️ Product Condition

Used product.
The circuit breaker shows normal signs of use and wear consistent with a used industrial component.
The photographs do not allow the electrical operation of the device to be certified.

📦 Package Contents

• 1 × ABB SACE Isomax S3N 250 4P
• Wiring/accessories visible in the photographs, if present and supplied together with the circuit breaker.

🟢 Summary

The ABB SACE Isomax S3N 250 4P is an ABB molded-case circuit breaker intended for the protection and isolation of industrial electrical circuits.
The configuration identifiable from the photographs is S3N 250, 4 poles, with Iu 250 A, Ue up to 690 V AC, Uimp 8 kV, and IEC 60947-2. ABB documents an Icu of 35 kA at 380/415 V for the S3N 250 version.
Compatibility Note: Before replacement, always verify the S3N model, number of poles, trip-unit type and settings, terminal configuration, and any installed accessories.