Product Overview
Type MM Size 4 Heavy Industrial Direct-Current Magnetic Switch
Condition
Unused new old stock. Preserved in clean storage; contact surfaces, operating linkages, and braided shunt leads show no wear. Mounted on an insulating backboard with rear threaded studs and includes a separate uninstalled arc chute piece as pictured. Markings legible on stamped nameplate: Westinghouse CONTACTOR TYPE MM422 S552D181G26 NP55956-B MADE IN U.S.A.
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Product Overview
Direct-current magnetic contactor built for demanding mill, crane, and heavy industrial motor control. The Type MM Frame 4 design handles heavy-duty DC power switching with magnetic blowout coils and molded arc chute structures to suppress arcing during contact opening. This assembly carries style number S552D181G26, complete with auxiliary contact interlocks, flexible copper shunt braids, and a rigid composite insulating backplate ready for panel mounting.
Key Features
- Type MM Frame 4 direct-current magnetic contactor assembly
- Westinghouse style number S552D181G26 with NP55956-B nameplate
- Two-pole contact structure with integral magnetic blowout arc interruption
- Heavy-duty braided copper shunt leads and solid terminal connection pads
- Auxiliary contact interlock block linked to the main operating armature
- Mounted on an insulating backboard with rear threaded mounting studs
- Includes one detached arc chute piece
Applications
- Maintaining legacy industrial DC crane, hoist, and mill motor control panels
- Replacing worn contactors in vintage heavy manufacturing machinery
- Custom high-current DC switching controls for heavy workshop equipment and power supplies
Frequently Asked Questions
What operating power does this contactor switch?
This is a DC contactor engineered for direct-current motor and power circuits, utilizing magnetic blowouts to extinguish DC arcs during contact separation.
What are the physical dimensions of the mounting plate?
The fibrous composite mounting plate measures 13.5 inches in length with rear threaded studs for panel installation.
What style number verifies interchangeability with an existing Type MM installation?
The stamped center nameplate confirms Type MM422 and style number S552D181G26, which matches Westinghouse replacement specifications for Frame 4 two-pole DC contactor assemblies.
Built for an industrial era when contactors were serviced with a wrench and copper shunts were made to outlast the machines they controlled. Bolt it into the panel and put heavy DC power back to work.
