RCD

Short for Residual Current Device. Protects against electric shock and fire risks.

Works by monitoring the residual current between the live and neutral lines.

Under normal operation, the residual current is . Generated magnetic fields cancel each other out.

When some current leaks to earth (like when someone touch the live wire), there will be a residual current. Which causes an unbalanced flux. Trips when the residual current exceeds the rated sensitivity (usually ).