초록 ▼

A circuit protection system employing arrangements of PTC devices and mechanical switches. The PTC device is not involved in the circuit until a fault is sensed. A current sensing relay senses an overcurrent and directs the current to the PTC device. As the voltage across the PTC device increases, a

A circuit protection system employing arrangements of PTC devices and mechanical switches. The PTC device is not involved in the circuit until a fault is sensed. A current sensing relay senses an overcurrent and directs the current to the PTC device. As the voltage across the PTC device increases, a parallel arrangement of voltage sensing relays completes the operation of the protection system, and disconnects the load until the protection system is reset. The protection system may be reset manually or remotely.

대표청구항 ▼

[ What is claimed is:] [1.] An electrical system which can be connected between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, the system having a normal operating condition and a fault condition, an

[ What is claimed is:] [1.] An electrical system which can be connected between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, the system having a normal operating condition and a fault condition, and comprising:(1) a current sensing means having(a) a current deenergized state, when the current passing through it does not exceed a normal current, I.sub.NORMAL, by a predetermined current amount, and(b) a current energized state, when the current passing through it has exceeded the normal current, I.sub.NORMAL, by the predetermined current amount;(2) a first circuit switch which is coupled with the current sensing means and which is(a) closed when the current sensing means is in the current deenergized state, and(b) open when the current sensing means is in the current energized state;(3) a voltage sensing means having(a) a voltage deenergized state when the voltage across the voltage sensing means does not exceed a predetermined voltage amount, and(b) a voltage energized state when the voltage across the voltage sensing means exceeds the predetermined voltage amount;(4) a PTC device; and(5) a second circuit switch which is coupled with the voltage sensing means and which is(a) closed when the voltage sensing means is in the voltage deenergized state, and(b) open when the voltage sensing means is in the voltage energized state; first circuit switch and the PTC device being connected in parallel with each other; the second circuit switch being connected in series with the parallel combination of the first circuit switch and the PTC device; and voltage sensing means being connected in parallel with the series combination of (i) the second switch and (ii) the parallel combination of the first circuit switch and the PTC device.