Definition
A reverse flow of electric current in a circuit, opposite to the normal direction of current flow. In aircraft electrical systems, back current most often refers to current flowing from the battery back into the generator or alternator when the generator output voltage drops below battery voltage.
Plain English
Electricity flowing the wrong way in a circuit. Normally the generator sends power to the battery; if the generator slows down or stops, the battery can start pushing power back toward the generator. That backward flow is back current.
Context Anchor
Seen in aircraft electrical system discussions, especially around batteries, generators, and protective switches that stop reverse flow.
Derivation
‘Back’ here means ‘in the reverse direction.’ ‘Current’ comes from the Latin currere, ‘to run’ — electrical current is literally the running or flow of electricity. So back current simply means electricity running backward through the circuit.
Why Pilots Care
Diodes block back current to protect batteries and generators from damage when the engine is off or during system faults.
Intuition Check
Do not read current here as airflow or a trend. Here, current means the flow of electricity, and back means that flow is going in the reverse direction.
Example Sentence 1
When the engine RPM dropped, the reverse-current cutout opened to prevent back current from flowing into the generator.
Example Sentence 2
A failed rectifier allows back current that can overheat and damage system components.