Frog: The Amphibian That Switches Trolley Poles

To most people, a frog is an amphibian: a small creature that hops between water and land, croaking at dusk. It has nothing to do with electricity, rails, or metal.

On an electric railway or streetcar line, a frog is a shaped metal device fitted into the overhead catenary wire system at track switches. When a trolley car changes tracks, its pole must move from one live wire to another without losing contact or arcing dangerously. The frog guides and redirects the trolley pole smoothly across this junction, allowing it to follow the conductor from the old wire onto the new one. The device's forked or angled geometry inspired its amphibian name: it straddles two paths, just as the animal straddles water and land.

The frog is a critical safety component. A badly designed or worn frog can cause the pole to bounce, interrupting power or creating sparks that damage both pole and wire. Maintenance crews inspect frogs regularly, checking for wear in the contact surfaces and proper alignment with the incoming and outgoing wires.

The metaphor runs deeper in textile production, where frogging means deliberately unravelling part of a finished piece to correct an error. Here too, the work changes direction: instead of continuing forward, the thread retraces its path backward. Though textile frogging predates electric railways, both uses share the idea of a device or action that forces a path to change course at a critical junction.