An Investigation of Current Interruption in Low-Voltage Circuits

The effect of circuit inductance on the performance of electrical contacts in low-voltage circuits has been investigated. The contact electrodes interrupt currents in the range 5 amperes to 15 amperes in a 6-volt circuit over a wide range of inductances, 0.1 H to 10 H. Measurements of the voltage transient across the opening electrodes show that an arc discharge occurs at all values of the circuit inductance. The duration of the arc is found to be proportional to the inductance. In an associated experiment, metal migration from cathode to anode and from anode to cathode is measured using a radioactive tracer technique. It is found that the metal transfer is strongly dependent upon the inductance, and hence the duration of the arc, even at the lowest values of the inductance. The effect of the rupture of the molten metal bridge and the subsequent micro-arc is discussed with relation to the observed metal transfer.