At the recent TMC meeting at Tampa, FL. the S. 1 Electrical study group held a panel discussion called “Who is watching the aux circuit?” Bruce Purkey moderated this session and there were three great presenters who shared their experiences with this issue.
· Jim Ohlmeire of TransAm told how his company had been using LED testers to test the aux circuit and the other circuits of the seven way cords. They assumed all was well because the lights were working. When they tried to utilize the aux circuit for a new charging system, they realized they had issues. They found corrosion and lack of maintenance had severely damaged the seven way cable’s capacity for current flow. He described the testing and maintenance procedures his fleet adopted to address this issue.
· Bob Rudolph of Haldex then told how important this circuit way to proper functioning of the ABS system on the trailer. He also told how other systems such as roll stability systems and communication systems were now using the aux circuit. He stated there is no real issue with sharing the circuit as long the most important safety related systems are given priority when multiple systems are running.
· Brad Van Ripper of Truck-Lite spoke as to how circuits that are powered off of the seven way cord are impacted by voltage drop. He told the audience that over 40% of fleets replace the green seven way cable with the cheaper black seven way cable that has smaller gauge wires for the aux, ground and stop light circuit. He highlighted the concern that the black seven way cable may not support the all systems on the trailer.
The bottom line is that our industry is paying enough attention to the aux circuit on the seven way cable, yet is increasingly utilizing it to supply power to more and more systems. The group agreed that new standard methods and procedures are needed to help fleets properly maintain this critical circuit.
