Oxidation
This is a conductive surface reacting with air and moisture and forming an insulating oxide layer. This layer raises the contact resistance and weakens the connection under load. It appears green-black on copper and as a thin, hard film on aluminium; aluminium oxide is particularly stubborn.
The oxide layer is very thin but electrically insulating. Its effect can stay hidden at small currents; when the current rises, voltage drops across the layer and the point heats up. This is why an oxidised connection can look fine on an ohmmeter and collapse under real load.
- Prevention: a correctly crimped connection forms a metal-to-metal cold weld and keeps air out of the contact surface; that is why it is considered gas-tight.
- Surface finish: tinned or nickel-plated terminals oxidise far more slowly than bare copper.
- Maintenance: when cleaning, protective grease is applied after abrasive paper or a wire brush; the grease goes on afterwards, not before.
- Moisture management: preventing condensation inside the enclosure directly slows oxidation.
On agricultural and machinery installations working outdoors, the connection points must be put on the periodic inspection list. An oxidised chassis connection is a frequently encountered silent cause of unstable operation complaints.
Context in which this term is used: Installation, redundancy and field continuity