Square D LJF36400U31X - 400 A, 600 V, 3-Pole Bolt-On Circuit Breaker | AmpState

The Square D LJF36400U31X is a rugged, three-pole bolt-on molded case circuit breaker designed for dependable branch circuit overcurrent and short-circuit protection in panelboards and loadcenters. With a 400 A rating and a 600 V capability, this device is built to handle demanding power distribution in commercial and light industrial settings, while still suitable for select residential applications that require higher load handling.

Key advantages that matter in the field

• Secure bolt-on mounting provides a rigid, vibration-resistant bus connection, helping maintain consistent electrical contact in environments with movement or vibration.
• Thermal-magnetic trip unit delivers stable, repeatable protection by responding to both overload and short-circuit conditions, helping prevent nuisance tripping while preserving equipment uptime.
• OEM-compatible design ensures reliable fit and performance with matching load centers and panelboards, reducing installation fit issues and ensuring coordinated protection.
• High-capacity protection 400 A at 600 V, three poles, ideal for main or feeder protection in larger distribution schemes and multi-branch circuits.
• Versatile applications suited for residential, commercial, and light industrial environments where robust, code-compliant overcurrent protection is required.

Technical snapshot

• Manufacturer: Square D
• Part Number: LJF36400U31X
• Type: Thermal-magnetic molded case circuit breaker
• Amperage Rating: 400 A
• Voltage Rating: 600 V
• Number of Poles: 3
• Mounting Style: Bolt-on
• Application: Branch circuit overcurrent and short-circuit protection

Who benefits from this breaker

• Facilities with large panelboards and loadcenters that require strong main or feeder protection
• Electrical installations in commercial spaces, light industrial facilities, and multi-family residences needing reliable three-phase protection
• Technicians seeking a durable, OEM-compatible solution to replace aging or failed breakers in Square D systems

Practical considerations and use scenarios

Install the LJF36400U31X in panelboards and loadcenters designed for bolt-on molded case breakers to ensure optimal contact and performance. Its thermal-magnetic trip mechanism provides predictable protection behavior under varying load conditions, reducing unexpected outages. When planning installation, verify compatibility with the existing OEM enclosure and ensure the mounting hardware and bus connections remain secure to maintain long-term reliability.

Why this matters in your power distribution system

• Reliable protection for critical equipment and circuits helps minimize downtime and potential damage from overcurrent events.
• The combination of bolt-on mounting and a robust thermal-magnetic trip unit supports consistent protection performance even in environments with vibration or mechanical stress.
• OEM compatibility simplifies replacements and maintenance, preserving system coordination and reducing retrofit challenges.