Winslow Co Type 301 Murray Varley Loop Cable Fault Locator Test Set

Winslow Co Type 301 Murray Varley Loop Cable Fault Locator Test Set

The Winslow Co Type 301 is a portable cable fault locator test set designed to pinpoint faults in buried or aerial cables using the Murray Loop and Varley Loop bridge methods. By connecting a known good conductor as a return loop and balancing a precision resistance bridge, a technician can calculate the exact distance from either end of a cable run to a ground fault, short, or open — narrowing the fault location to within feet over runs stretching miles. This is a classic piece of telephony and power cable infrastructure test gear, housed in its original oak carrying case with full operating instructions mounted inside the lid.

Specifications & What's Included

• Manufacturer: The Winslow Co., New York
• Model: Type 301
• Test methods: Murray Loop, Varley Loop, Simple Varley, Three-Cable method
• Resistance network: Four decades of precision step resistors
• Resistance range: 1 ohm to 10,110 ohm
• Multiply dial: front-panel ratio/multiply selector
• Decade dials: ×1000, ×100, ×10, ×1 step resistor dials
• Built-in analog galvanometer (center-zero)
• Cam-style function switches (INT/EXT galvanometer, RES/VAR/MUR selector)
• Binding posts for loop connections
• Power source: internal dry cell batteries (battery compartment in case base)
• Enclosure: oak wood carrying case with brass corner fittings and metal latch
• Operating instruction card glued inside lid — Murray Loop, Varley Loop, and Three-Cable formulas and wiring diagrams
• Leather carrying handle: missing

Applications

Murray and Varley loop test sets like the Type 301 were standard equipment for telephone companies, telegraph operators, and power utilities from the late 19th century through the mid-20th century. The Murray loop method uses a Wheatstone bridge principle: the faulty conductor and a good return conductor are joined at the far end to form a loop, and resistance ratios are balanced on the decade dials until the galvanometer reads zero — from which the fault distance is directly calculated. The Varley method is a variation that uses a rheostat and fixed ratio resistors, better suited for cables with high loop resistance or for measuring open faults. These instruments were used by telephone plant engineers to locate faults in lead-sheathed cable pairs, aerial open-wire lines, and submarine cable sections without having to dig or physically inspect the entire run. The Type 301 specifically dates from the early-to-mid 20th century — identifiable by its oak and brass construction, bakelite dial knobs, and dry-cell battery power, all hallmarks of that era's field test instruments. Today these sets are collected by vintage electrical instrument enthusiasts and by museums and historical societies documenting early telecommunications infrastructure.