Abstract: A device for rapidly discharging without arcing a high-tension DC voltage source includes a cylinder of an insulative material in which slide two electrode pistons. These are equipped with internal auxiliary pistons which carry needles which can be deployed so as to project beyond the domed ends of the electrode pistons. The electrode pistons are connected to the terminals of the high-tension voltage source. When compressed air is fed into the central part of the cylinder, the electrode pistons and the auxiliary pistons are driven towards the ends of the cylinder. The rounded domes and the increased pressure of the air provide a high degree of insulation. Once the high-tension DC voltage source has been switched off, the center of the cylinder is vented to atmosphere. The auxiliary pistons are driven towards one another by springs, entraining the electrode pistons and deploying the needles.