49 C.F.R. § 236.723 Circuit, double wire; line.
Title 49 - Transportation
An electric circuit not employing a common return wire; a circuit formed by individual wires throughout.
Title 49: Transportation
PART 236—RULES, STANDARDS, AND INSTRUCTIONS GOVERNING THE INSTALLATION, INSPECTION, MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCES
Subpart G—Definitions
§ 236.723 Circuit, double wire; line.