Definition
A two-terminal electronic component whose electrical resistance varies with the voltage applied across it. At low voltages it acts as a near-insulator, but once the applied voltage exceeds a specific threshold its resistance drops sharply, allowing current to pass. This behavior makes it useful for protecting circuits from voltage spikes.
Plain English
An electrical part that normally blocks current, but suddenly lets current flow if the voltage gets too high. It is used to absorb electrical surges and protect sensitive equipment.
Context Anchor
Seen in aircraft electrical-system and avionics maintenance discussions, especially where equipment needs protection from voltage spikes.
Derivation
Formed from 'variable' + 'resistor' — literally a resistor whose value varies. Knowing this makes the function easy to remember: its resistance is not fixed.
Why Pilots Care
Prevents damage to avionics and electrical components from transient voltage spikes that can occur during engine starting or generator malfunctions.
Analogy
A varistor is like a pressure relief path for unwanted electrical pressure. Under normal conditions it does little, but when voltage rises too high, it gives the surge a safer path and helps keep sensitive equipment from being hit directly.
Intuition Check
A varistor is not a cockpit control or a manually adjustable resistor. It is an automatic protective part inside an electrical circuit.
Example Sentence 1
A varistor is installed across the radio's power input to absorb voltage spikes from the aircraft electrical system.
Example Sentence 2
During the preflight electrical check, the mechanic verified that the varistor had not failed and was still providing overvoltage protection.