Making Connections

Electric railway systems normally use a single overhead wire to bring power to the train; and they use the running rails as the current return path back to the power station. There are variation on the theme: dual overhead wire, third rail, and underground conduit; but normally it's single overhead wire. Copper is the wire of choice for overhead because of its low resistance, high strength, and moderate cost. Using the rails for a return path has its own set of compromises. Steel is plenty strong, and rails have a large cross-section to handle the return current. The biggest problem occurs at the rail joints because steel rails rust - and iron oxide is non-conductive. To compensate, electric railways must join their rails together to form an unbroken path back to the power station. You can see that work in progress in this photo.


In the old days, a mold - containing thermite charges and a copper bond wire - was placed across the rail joint, and then lit on fire. The thermite melted the steel rails enough to fuse the bond wire into the rails. We have the equipment to do thermite bonds, but we've elected to use a newer method. We're using a big MIG welder to make the rail bonds. The bonds we use have a steel bar on each end of the wire; and you can weld those bars directly to the rails - if your MIG has enough power. In the next picture, you can see a finished rail bond in place.


Every joint on the railroad needs one of these bonds before the trolley cars will run again. We are only bonding one of the two rails; but there are still a couple hundred bonds to install - and later inspect and repair. George Epperson and Bob Clarke have been working on this project for two weeks. They are getting close, but they still have a ways to go.