49 C.F.R. § 234.231 Fouling wires.
Title 49 - Transportation
Each set of fouling wires in a highway-rail grade crossing train detection circuit shall consist of at least two discrete conductors. Each conductor shall be of sufficient conductivity and shall be maintained in such condition to ensure proper operation of the train detection apparatus when the train detection circuit is shunted. Installation of a single duplex wire with single plug acting as fouling wires is prohibited. Existing installations having single duplex wires with a single plug for fouling wires may be continued in use until they require repair or replacement.
Title 49: Transportation
PART 234—GRADE CROSSING SIGNAL SYSTEM SAFETY
Subpart D—Maintenance, Inspection, and Testing
Maintenance Standards
§ 234.231 Fouling wires.
