McDonnell & Miller 310462 Switch Assembly

The McDonnell & Miller 310462 (Model SWA-150S) is a heavy-duty snap-action switch assembly designed for precise low water cut-off and pump controller transitions. This automatic reset assembly is a critical replacement component for Series 150S and Series 157S mechanical boiler controls. Built to manage steam boiler water levels up to a maximum operating pressure of 150 psi, the SWA150S provides reliable SPDT switching to prevent dry-fire conditions and maintain optimal pump operation.

When installing this boiler control replacement part, ensure the system is cooled to 80°F and pressure is at 0 psi. The snap switch assembly is specifically calibrated for 150S series heads and is not interchangeable with older mercury switch models. Techs should verify the actuator assembly alignment and ensure all electrical connections are wired in series with existing operating limits. This assembly maintains a 7.4A rating at 120 VAC for pump circuits, making it the standard for commercial steam heating systems requiring automatic reset functionality.

Key Benefits:

• Optimized Compatibility: Direct drop-in replacement for McDonnell & Miller Series 150S and 157S controllers.
• Reduced Arcing: High-quality snap-action mechanism ensures crisp contact breaking to extend component life.
• Boiler Safety: High-side automatic reset protects against low-water incidents without manual intervention.
• Broad Application: Rated for systems up to 150 psi, covering most commercial and industrial low-pressure steam applications.
• Precise Control: Facilitates tight differential pressure management for pump-on and burner-off setpoints.

Common Questions:

Can I use the SWA-150S to replace an old mercury switch?
No. Snap switch assemblies for the 150S series are not interchangeable with mercury-style 150 series controls. If you are converting, a full head replacement (150S-HD) may be required.

What are the electrical load limits for this switch?
The 310462 switch assembly is rated for 7.4A at 120 VAC or 3.7A at 240 VAC. For larger motor loads, you must use a dedicated starter or relay to prevent contact welding.

Does this assembly include the actuator arm?
The SWA150S typically includes the switch blocks and mounting bracket. It is recommended to inspect the internal float and rod for scale buildup during installation to ensure smooth mechanical movement.

This item is not eligible for free shipping.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.