Current disruptions may be excited spontaneously in a laboratory plasma when the electric current density along the magnetic field is large. This phenomenon is investigated in the plasma column of a triple plasma device with an inductive external electric circuit. Each current disruption then gives an inductive voltage pulse of several hundred volts over the plasma, and this potential drop is found to be concentrated at an electric double layer which forms in the plasma during the pulse. Most of the magnetic energy, initially stored in the circuit inductance, is transferred to the double layer during the period of current decrease and released there as particle energy. Simultaneously as the current decreases the potential level at a local potential minimum in the plasma is found to decrease. Reflection of electrons at this minimum is conjectured to cause the decrease of the current during a disruption.