Siemens | MQJ390 | Circuit Breaker | 90A | 3-Pole | 240V

Meet the Siemens MQJ390 Circuit Breaker — a dependable 90A, 3-Pole unit designed for 240V systems. Built to support maintenance, retrofit, and replacement projects where exact specifications matter, this breaker helps ensure reliable protection and minimizes downtime in demanding electrical setups.

Key specifications

• Amperage: 90 A
• Poles: 3-Pole
• Voltage: 240 V
• Part number: MQJ390

Why this matters

Having the exact part number — MQJ390 — on hand is the straightforward way to confirm compatibility with your Siemens equipment or compatible panels. Before ordering, verify fit and ratings to avoid mismatches in bus configuration or trip characteristics that could affect protection levels or wiring safety. This unit is specifically suited for 3‑phase, 240V installations where a 90A protective device is needed.

What makes it unique

• Direct-fit replacement for existing Siemens installations with the MQJ390 reference
• Three-pole design provides coordinated protection across all live conductors in 240V systems
• Reliably built for maintenance and retrofit workflows, reducing downtime
• Ideal for upgrading protection in retrofit projects or stocking spares for quick service

Practical use cases:

• Replacing a worn or failed breaker in 240V, 3-phase panels when the original unit matches MQJ390
• Retrofit projects upgrading panel protection to a 90A capacity without altering the panel footprint
• Maintenance planning in commercial or industrial environments that require stable, predictable protection

Tip: Always cross-check with your panel labeling and the original equipment manufacturer guidance. While MQJ390 is the primary compatibility reference, confirming the exact fit and ratings with your current installation ensures safe, compliant operation.