Definition
The electrical resistance offered by the insulating material surrounding a conductor, measured between the conductor and ground or between two conductors. High insulation resistance indicates the insulation is doing its job of preventing current from leaking out of the wire; low insulation resistance indicates the insulation has degraded and current is escaping where it should not.
Plain English
A measurement of how well the covering around a wire is keeping the electricity inside the wire, where it belongs. A high number means the covering is working. A low number means electricity is leaking through it.
Context Anchor
Seen in aircraft electrical maintenance, especially when checking wiring, generators, motors, ignition parts, or other equipment for damaged or aging insulation.
Derivation
Insulation comes from the Latin insula, meaning island — the idea is that the conductor is kept on its own electrical island, separated from everything around it. Resistance is the opposition to current flow. Together: how strongly the insulating material resists letting current escape.
Why Pilots Care
Low readings indicate deteriorating insulation that can cause shorts, ground faults, equipment failure, or fire.
Grounding Statement
A good insulated wire keeps electrical current inside the wire path; poor insulation lets some of that current escape where it should not.
Intuition Check
Insulation here does not mean keeping something warm. It means separating electricity from nearby metal, wires, or structure so current does not leak where it should not go.
Example Sentence 1
The technician measured the insulation resistance of the generator windings and found a reading low enough to warrant replacement.
Example Sentence 2
Before installing new avionics, the technician verified insulation resistance on all associated wiring runs.