It’s a common question—and a common mistake. While copper wire might seem like an easy and affordable option for extending a thermocouple, doing so can lead to inaccurate temperature readings and unreliable measurements.
Why People Think Copper Wire Is OK
Many people assume copper wire is acceptable because:
- It looks like regular wire and is familiar.
- There’s a belief that “wire is wire,” and all conductors behave the same.
- For short extensions, some think the impact will be negligible.
- Thermocouple theory isn’t widely understood—many people don’t realize that accurate voltage readings depend on using specific metals consistently throughout the entire cable run.
- In low-accuracy applications, it might even “seem” to work—until it doesn’t.
Why It’s Actually a Problem
Thermocouples rely on the Seebeck effect, which produces a voltage based on the temperature difference between two dissimilar metals. Here’s what goes wrong when you use copper wire:
- Incorrect Materials
Copper doesn’t match the thermoelectric properties of thermocouple wires like Chromel, Alumel, or Iron. Splicing copper in creates extra junctions that behave like unintended thermocouples.
- Distorted Readings
These new junctions generate additional voltage that interferes with the true signal, leading to false temperature readings.
- Temperature Gradient Issues
Any temperature differences along the copper extension create unintended thermoelectric effects that throw off the sensor’s output.
- Calibration Errors
Thermocouples are calibrated based on the specific thermoelectric properties of their metal types. Introducing copper into the circuit disrupts this calibration, resulting in unreliable measurements.
The Right Way to Extend Thermocouple Wires
Always use thermocouple extension wire that matches the type of thermocouple you're using (e.g., Type K, J, T, etc.). These wires are made with the same or compatible materials to preserve measurement integrity and ensure accurate signal transmission.
Need help choosing the right extension wire for your application? Contact our team for guidance!