Circuit Protection Devices

What is a Circuit Protection Device? A circuit protection device is a current or voltage sensitive device that protects a circuit from either overcurrent or overvoltage conditions. Fuses Unlimited offers a broad range of circuit protection devices. Our circuit protection product offering includes a variety of types of circuit protection devices. Overcurrent products include fuses, fuse clips, fuseholders, fuse blocks, circuit breakers and positive temperature coefficient (PTC) resettable devices. Overvoltage products include Metal Oxide Varistors (MOV's), discreet transient voltage suppression diodes (TVS Diodes), TVS diode arrays, protection thyristors, electrostatic discharge suppressors (ESD) and gas discharge tubes (GDT's).

Circuit Breakers are mechanical circuit protection devices. Hydraulic Magnetic Circuit Breakers have a coil, an iron core sealed in a tube filled with hydraulic fluid, a spring loaded actuator and two electrical contacts. When excessive current from a current overload runs through the device, the electromagnetic field in the coil is increased which moves the iron core through the tube and causes the spring loaded actuator to trip, separating the contacts and opening the circuit. Opening speed is determined by the viscosity or thickness of the hydraulic fluid. Thermal circuit breakers utilize a bimetal strip that deforms from the heat generated from an overcurrent condition to trip the breaker and open the circuit. Thermal Magnetic circuit breakers utilize a bimetal strip to activate the breaker in a current overload condition and a spring actuated electromagnetic coil to activate the breaker in a short circuit conditions.

PTC Devices are made of a special polymer material that changes its state in response to the heat generated from an overcurrent condition which opens the circuit. When the overcurrent condition is removed, the material reverts to its original state and closes the circuit. A Positive Temperature Coefficient Device is also referred to as a PTC Device or a Resettable Fuse.

Varistors are voltage sensitive devices designed to protect circuits against transient voltage surges. Multilayer Varistors (MLV's) are surface mount devices that utilize a ceramic multilayer-layer construction and are used to protect circuit boards in small electronics from transients generated from electrostatic discharge (ESD), inductive load switching and lightning surge remnants. Metal Oxide Varistors (MOV's) are epoxy encapsulated zinc oxide discs with radial or axial leads. MOV's are mid-range devices used to protect small machinery, power sources and components.

TVS Diodes are discreet, fast switching, semiconductor devices that can respond to overvoltage events faster than most other types of circuit protection devices. It is a Crowbar Device that is useful for protecting against very fast and damaging voltage transients, such as lightning, inductive load switching and electrostatic discharge. TVS stands for discrete transient voltage suppression.

Sensing Products include the reed switch, the reed sensor, the reed relay, the Hall Effect sensor and temperature sensing thermistors and RTD's. Typical applications include the sensing of proximity, liquid level, liquid flow, speed and temperature.