The Invention
The patent, US395538A, granted to Granville T. Woods of Cincinnati, Ohio, on January 1, 1889, is for a safety device for electric circuits. The invention’s purpose is to automatically shut off the power from a generator in case of a break or fault in the main conducting wire. This was a critical safety feature for early electric lighting and power systems.
Key Features:
- Circuit-Breaking Armature: The central component of the invention is a circuit-breaking armature (c). This is a small, pivoted piece of metal that acts as a switch, connecting the generator to the main conducting line.
- Auxiliary Return Wire: The main conductor (B) is paired with an auxiliary return wire (E). These two wires run parallel to each other.
- Electromagnet Control: The armature is controlled by an electromagnet (e) that is powered by the auxiliary return wire.
- Normal Operation: In a healthy circuit, current flows from the generator, through the armature, into the main conductor, and returns via the auxiliary wire to power the electromagnet. The electromagnet’s magnetic pull holds the armature in place, keeping the circuit closed and the power flowing.
- Automatic Shut-Off: If the main conductor wire breaks at any point, the circuit is interrupted. The current stops flowing through the auxiliary return wire, causing the electromagnet to lose its power. A retractile spring (s) then pulls the armature away, automatically opening the circuit and cutting off the power from the generator. This prevents dangerous situations like live wires falling to the ground.
- Protection from Sagging: Woods also includes a clever feature to protect against a “mere displacement” like a wire sagging. He adds small insulated links (f) that connect the main conductor to the auxiliary return wire. If the main wire sags too much, these links apply a strain that is designed to break the weaker auxiliary wire, which in turn de-energizes the electromagnet and shuts off the power.
Significance of the Invention and Inventor
Granville T. Woods was a pioneering African American inventor who made immense contributions to electrical and railway technology.1 This patent is a testament to his focus on safety and reliability.
- Revolutionizing Electrical Safety: In the early days of electrification, power lines were a major public safety hazard. This was especially true for arc lighting systems, which operated at high voltages. A broken or sagging wire could be deadly. Woods’s invention was a simple yet brilliant solution to this problem, providing an “automatic” fail-safe that could prevent accidents. It was a crucial step in making electric power a more viable and safer technology for widespread use.
- An Innovative System Designer: This patent demonstrates Woods’s skill not just as an inventor of a single device, but as a systems designer. He created a coordinated system of components—the armature, the electromagnet, and the auxiliary wire—that worked together to achieve a high level of safety and reliability. His foresight in including a solution for “sagging” wires shows his deep understanding of the practical challenges of electrical infrastructure.
- A Prolific Legacy: This patent is one of dozens held by Woods, a testament to his prolific output and wide-ranging expertise.2 Despite facing racial prejudice and legal battles, his work was consistently ahead of its time. His innovations in electrical safety, railway telegraphy, and motor technology were fundamental to the development of modern electrical systems and transportation networks.
