A method to achieve arcless interruptions in low current circuits

In most existing low current interruption devices, the current is interrupted using only separating contacts. By adding a ceramic PTC (CPTC) element in parallel with the contacts, 100% of the interruption energy can be converted to heat, eliminating the are totally. The initial voltage across the contacts must be less than a pre-determined value in order to shunt all of the current to the CPTC. The cold resistance of the CPTC is the main factor in determining the initial voltage across the contacts and the current at which the CPTC trips. Two types of ceramic PTC devices were tested, with cold resistances of 16 and 32 ohms respectively. In the case of each device, at 300 Vdc and 1.0 A, all of the interruption energy was consumed by the CPTC. At 300 Vdc and 1.5 A, the 16 Ohm CPTC successfully absorbed 100% of the interruption energy; however, the 32 Ohm CPTC device had a slightly lower performance at 98%. Because of the elimination of arcing, use of the CPTC in low current interruption devices will result in reduced contact size and increased operation cycles. It will also provide an arcless interruption for application in hazardous conditions.