Why Third Rail Trains Use a Shoe Instead of a Wheel for Contact

When we consider the evolution of third rail trains, one fascinating aspect is the choice to use a contact shoe rather than a wheel for electrical contact. This decision, made early on, has numerous practical advantages that have stood the test of time. The history of electrical collection systems for trains, especially those using third rail systems, is rich with experiments, challenges, and improvements. In this article, we delve into the reasons why shoes are preferred over wheels and explore how this choice has influenced the design and functionality of modern trains.

Early Experiments and Challenges

Understanding the early trams provides insight into the development of contact systems. Early trams often used grooved wheels to contact the overhead wire for current collection. However, as the technology evolved, the wide contact shoe pantograph became a more effective solution. The advantages of this system were numerous, including a broader contact surface that avoided sparking and extended the life of the electrical contact surfaces.

The Drawbacks and Innovations

A scaping shoe, which is a type of shoe contact, was more efficient in managing thin layers of ice over the rail. During winter operations, a train encountered on a track with a thick snow cover found it difficult to gather power from the rail. Arcing could melt the snow and snow would eventually melt to maintain power; however, this process was temporary. If the train continued to operate over the icy and snow-covered rail, it would eventually lead to a breakdown of the electrical system. The key issue was that a wheel, which provides only a minute contact area, would be far less effective at managing ice and snow. The shoe, on the other hand, offers a much better contact surface, ensuring more reliable current collection in adverse conditions.

Practical Advantages and Innovations in Tram Technology

Trams evolved significantly as they grew in size and power requirements. The transition from trolley wheels to fixed shoe sliding heads and eventually to bow collectors and pantographs was a testament to the continuous improvement in contact systems. One of the main deficiencies of trolley wheels was the consistent arcing, particularly evident in the dark. As technology advanced, carbon inserts were introduced to overcome this issue. R. Edgeley-Cox, the transport manager and chief engineer of the Corporation Transport department, experimented with these carbon inserts. The results were impressive, drastically reducing arcing issues. However, a new challenge arose with heavy rain.

Water washed out the carbon dust that was created and deposited over the top and sides of the bus, leading to an unsightly appearance on a royal blue paint job. To solve this, the mounting points were extended by a few feet and moved a couple of feet back, allowing the carbon to drop onto the road behind the bus rather than onto its body. A conductor’s practical response to the possibility of drivers’ complaints was: "Their own darned fault for driving too close to the bus".

Impact and Legacy

The transition to carbon shoes, while effective, faced challenges such as aesthetic issues and maintenance needs. Many trolley buses and trams continued to use trolley wheels or pantographs, and the legacy of experimentation with different contact systems remains. During World War II, the supply of carbon was directed to power stations and military equipment, leading to the re-fitting of many trolley buses with the traditional trolley wheels. This practice continued until more advanced systems became more prevalent.

The choice of using a shoe instead of a wheel for third rail contact is not just a historical matter but a decision influenced by practical advantages in terms of efficiency, reliability, and safety. Despite occasional challenges, the shoe system has proven itself to be a robust and effective method for modern trains and trams.

Keywords: third rail, shoe contact, electrical contact surfaces, tram development, ice management