Definition
A current-limiting device that uses an incandescent lamp filament, typically made of iron wire in a hydrogen-filled bulb, to keep current relatively constant in a circuit. As current through the filament increases, the filament heats up and its electrical resistance rises, which in turn restricts further current flow. This self-regulating behavior protects sensitive components from current surges.
Plain English
A special light bulb wired into a circuit to keep the electric current steady. When the current tries to rise, the bulb's filament heats up and resists the flow, holding the current near a set value.
Context Anchor
Seen in older aircraft electrical systems, equipment manuals, and maintenance troubleshooting for circuits that need current limiting or current stabilization.
Derivation
Ballast comes from a Middle English word for the heavy material placed low in a ship to keep it stable. The term was borrowed into electrical work to describe a component that stabilizes a circuit. A ballast lamp stabilizes current the way ship's ballast stabilizes a vessel.
Why Pilots Care
Ensures steady current to lights and instruments in legacy aircraft without overloading circuits or causing flickering.
Analogy
It is like using a narrow section in a water line to keep the flow from becoming too strong. The ballast lamp helps restrain the flow of electricity in the circuit.
Intuition Check
Do not assume “lamp” means its main purpose is lighting. In “ballast lamp,” the lamp is used mainly to control electrical current.
Example Sentence 1
The mechanic traced the radio fault to a burned-out ballast lamp in the power supply circuit.
Example Sentence 2
Before flight the pilot confirmed the ballast lamp was glowing evenly, indicating the circuit was properly regulated.