Less heated air is extracted to outside, and less electricity consumed if the fan operates only while work is in progress. Switch the fan on/off manually at the hood, or automatically with a sensor clamp. Single-phase power supply to the operation box. The automatic fan control has a sensor clamp to be attached to the earth cable of the welding set for automatic start-up of the fan. Detects currents from 8 A. The operation box consists of a 30 VA transformer for the lighting kit in the extraction arm, a delay timer for fan stop variable from 0-5 minutes, and two separate connections for sensor clamps.