Square D 9421LR4 400A Circuit Breaker, NEMA 3R, NEMA 1 | AmpState

Meet the Square D 9421LR4 400A circuit breaker — a robust, genuine protection device engineered for reliability in both outdoor and indoor electrical distributions. With NEMA 3R weatherproof suitability for outdoor installations and NEMA 1 indoor versatility, this breaker is built to handle the demands of modern panelboards, load centers, and distribution systems without compromise.

Why this breaker stands out

• Dual weather ratings in one part: NEMA 3R compatibility for outdoor, weather-exposed configurations and NEMA 1 suitability for indoor use — giving you flexibility across site conditions without carrying multiple parts.
• Exact BOM alignment with Square D systems: Part number 9421LR4 ensures seamless replacement in existing installations, preserving electrical characteristics and footprint to avoid compatibility surprises.
• High-current protection rated at 400 A, making it ideal for feeder and distribution applications where consistent, reliable interruption protection is essential.
• Strategic spare and replacement option: A dependable choice for maintenance inventories, service upgrades, retrofits, and long-term asset management — align your bill of materials with the original part to simplify ordering and reduces downtime during replacements.

Perfect for

• Replacement projects in commercial or industrial facilities that use Square D panels and load centers
• Service vans and maintenance programs that require on-hand spares to minimize downtime
• Projects where BOM alignment is critical to maintain system compatibility and performance

What you can expect in practice

• Reliable overcurrent protection to safeguard wiring, devices, and downstream equipment per 400 A application needs
• Consistent performance across indoor and outdoor environments thanks to its dual NEMA-rated design
• A straightforward fit for original installations, reducing the risk of adverse electrical interactions or misfits

Need help confirming fit? If you’re unsure about compatibility with a specific panelboard or distribution setup, send us a message and we’ll help verify the match to your exact equipment.

Availability is provided by AmpState, making it easier to source this genuine Square D part when you’re planning replacements or stocking spares. For professional installation, rely on a qualified electrician and follow all applicable electrical codes and safety guidelines.