US lawFederal (United States)RegulationsTitle 49 CFR — TransportationChapter II — FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATIONPart 236 — RULES, STANDARDS, AND INSTRUCTIONS GOVERNING THE INSTALLATION, INSPECTION, MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCESSubpart G — Definitions236.72149 C.F.R. § 236.721Circuit, control.Last amended: 2017Year: 2026Length: 15 wordsOfficial source Cite as 49 C.F.R. § 236.721 (2026)An electrical circuit between a source of electric energy and a device which it operates.Previous49 C.F.R. § 236.720Next49 C.F.R. § 236.722