Southwire MSTR-300-B Liquid-tight Straight Connector 3 in

Product Description

The SOUTHWIRE MSTR-300-B is a 3-inch straight liquid-tight box connector designed for secure, watertight conduit terminations at electrical enclosures and junction boxes. Constructed from malleable iron with an insulated throat, this connector resists mechanical stress and protects conductors from abrasion at the entry point. It is used by licensed electricians wherever liquid-tight flexible metal conduit (LFMC) or liquid-tight flexible nonmetallic conduit (LFNC) must be terminated in wet, oily, or corrosive environments. The straight configuration suits direct entry applications where a 90-degree fitting is not required.

This connector is suited for industrial, commercial, and heavy-duty residential installations. Typical applications include machine tool wiring, HVAC equipment connections, pumps, compressors, and outdoor electrical enclosures where moisture ingress must be controlled. The 3-inch trade size accommodates large-diameter liquid-tight conduit runs commonly found in high-ampacity branch circuits and equipment feeder connections. This part is also referenced by Madison as MSTR-300-B and by Topaz as 478S.

Key Features

• Straight configuration for direct conduit-to-box terminations without angular offset
• Malleable iron body for durability and resistance to mechanical impact
• Insulated throat protects wire insulation from abrasion at the connector entry
• Liquid-tight design seals against moisture, oils, and contaminants
• 3-inch trade size for large-diameter conduit applications

Compatibility

Designed for use with 3-inch liquid-tight flexible metal conduit (LFMC) and liquid-tight flexible nonmetallic conduit (LFNC) in standard knockout termination applications. Cross-referenced with Madison MSTR-300-B and Topaz 478S.

Installation Notes

Installation should be performed by a licensed electrician in accordance with the National Electrical Code (NEC). De-energize all circuits and lock out the panel before beginning work. The connector is tightened using an appropriately sized wrench on the locknut and connector body — do not overtighten malleable fittings. Verify that the conduit sealing ring is properly seated to maintain the liquid-tight integrity of the connection.

Technical Specifications

• Trade Size: 3 inches
• Configuration: Straight
• Body Material: Malleable iron
• Throat: Insulated
• Conduit Type: Liquid-tight flexible metal or nonmetallic conduit

Standard Information

• Brand: SOUTHWIRE
• Manufacturer Part Number: MSTR-300-B