Why does the current display value change when the welding wire extension length changes during CO2 welding?

During CO2 welding, changes in the wire extension length (dry extension) will cause changes in the current display value, mainly for the following reasons:

**Resistance Heating Effect:** The longer the wire extension, the greater its resistance. According to Joule's law (Q=I²Rt), increased resistance means more current is used to heat the wire itself (i.e., resistance heat loss) rather than for the welding arc. Therefore, the current display value will decrease due to the shunting effect of resistance heat, and the actual welding current will also decrease accordingly.

**Melting Rate and Current Matching:** Increasing the wire extension length will accelerate its melting rate (due to increased resistance heat), but the welding current is regulated by the wire feed rate. If the two are mismatched (e.g., melting rate > feed rate), it will lead to arc instability, further affecting the accuracy of the current display value.

**Melting Rate and Current Matching:** Increasing the wire extension length will accelerate its melting rate (due to increased resistance heat), but the welding current is regulated by the wire feed rate. If the two are mismatched (e.g., melting rate > feed rate), it will lead to arc instability, further affecting the accuracy of the current display value. Impact of Standard Parameters
Welding current and wire extension length must be matched:

For current ≤200A, a wire extension length of 10-15mm is recommended;
For current 200-350A, 15-20mm is recommended;
For current 350-500A, 20-25mm is recommended.

Exceeding the reasonable range (e.g., too long) can easily lead to spatter, insufficient penetration, or unstable arc, indirectly affecting the current display.

00:00 Importance of Wire Extension Length

00:10 Calculation Formula for Wire Extension Length

00:32 Impact of Excessively Long Wire Extension

00:41 Impact of Excessively Short Wire Extension

01:01 Relationship between Wire Extension Length and Current

Summary: Wire extension length interferes with stable current output by altering resistance heating and melting speed. Therefore, it must be strictly controlled within the range of 12-20mm (generally recommended), and specific parameters should be adjusted according to the current magnitude.