Contact vs Transistor output
Written by Luke Ellacott
Updated at May 6th, 2026
Scenario
In automation systems, digital outputs are commonly either contact (relay) outputs or transistor outputs. Both are used to switch signals ON and OFF, but they operate in different ways.
| Feature | Contact Output (Relay Output) | Transistor Output |
|---|---|---|
| Operation Type | Mechanical switch with moving parts | Electronic switching (no moving parts) |
| How it Works | Metal contact physically opens/closes | Electronic component controls current flow |
| When ON | Contact closes, current flows | Allows current to flow |
| When OFF | Contact opens, current stops | Blocks current flow |
| Voltage/Current Capacity | Supports wider voltage range and higher current | Supports lower voltage and current range |
| Speed | Slower due to mechanical movement | Faster switching |
| Durability | Wears over time (mechanical parts) | Longer lifespan (no mechanical wear) |