MDI Mercury Displacement 235NO-24A-18 Contactor

The MDI Mercury Displacement 235NO-24A-18 Contactor is a heavy-duty, 2-pole switching solution engineered for high-cycle industrial HVACR applications. This 35 amp mercury contactor features a 24V AC coil and is designed for normally open operation, providing a reliable interface for controlling resistive loads like electric heaters or high-intensity lighting. Unlike standard mechanical relays, this mercury displacement relay utilizes a liquid mercury contact medium, which eliminates contact bounce and significantly reduces arcing. This hermetically sealed construction ensures the unit is resistant to dust, moisture, and oil contamination, making it a preferred choice for harsh mechanical rooms. The "-18" suffix indicates the inclusion of metal straps around the poles for enhanced structural durability compared to standard nylon-strapped versions like the 235NO-24A. Pro-tip for the field: these units must be mounted vertically to ensure the mercury pool properly bridges the internal plunger and electrodes. With no internal moving parts to wear out like traditional armatures, this low-maintenance HVAC contactor is built for millions of cycles in demanding environments.

• Arc-Free Switching: Liquid mercury contacts prevent the pitting and erosion common in mechanical alternatives.
• Hermetically Sealed: Encapsulated in high-grade epoxy and glass-to-metal seals for operation in contaminated environments.
• Enhanced Durability: Features a metal pole strap (-18 variant) for superior physical stability in industrial panels.
• Silent Operation: The displacement mechanism eliminates the loud "clack" associated with traditional magnetic starters.
• High-Cycle Rating: Capable of millions of operations, making it ideal for rapid-cycling resistive heating elements.

Can I use this contactor for motor loads?
The standard 235NO-24A-18 is Argon-filled and optimized for resistive HVAC loads. For inductive motor applications, veterans typically look for the "H" (Hydrogen-filled) variant to manage back-EMF more effectively.

Are there specific mounting requirements for this part?
Yes. Because it relies on gravity and mercury displacement, the unit must be mounted in a vertical position. Deviating from a vertical orientation will cause the contacts to fail to close or open correctly.

What is the difference between the 235NO-24A and the 235NO-24A-18?
The units are functionally identical in electrical specs (35A, 24VAC, 2P); however, the -18 model includes heavy-duty metal straps securing the poles, whereas the base model uses nylon straps.

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.