EWTH is well suited for DCEN and not suitable for which?

• A. AC
• B. DCEN
• C. DCSP
• D. None

Answer: (A)

In GTAW, the type of tungsten electrode and the current polarity together determine arc stability and electrode wear. Thoriated tungsten (EWTH) provides excellent electron emission and arc stability at higher currents when using direct current with the electrode negative (DCEN). That setup concentrates heat in the workpiece and helps you weld thicker sections with good control, while the electrode remains durable and easy to start the arc.

But alternating current (AC) reverses polarity rapidly, which changes how the electrode tip behaves. Under AC, the thoriated tip is more prone to rapid wear, tip contamination, and unstable arc characteristics, making it less reliable. For AC, other tungsten types such as pure tungsten or ceria/lanthanated tungstens are preferred because they handle the frequent polarity changes better and maintain a stable arc.

So EWTH is best for DCEN due to strong emission and arc stability in that polarity, and is not suitable for AC because its performance degrades with the rapid polarity switching.