Abstract: To control the plasma arc in accordance with the present invention, the pressure change characteristics or curve in a torch is determined from the moment a plasma forming gas is delivered thereto until this plasma forming gas reaches the pressure in the supply manifold. Such a measurement is done for each selected cutting condition characterized by a constant flow rate of the plasma forming gas. The arc supply current is then fed in two stages: at first by a jump to a current amounting to approximately half the cutting current for a selected condition and then by gradually increasing the current in compliance with the pressure change characteristics or curve until the cutting current value is attained.