PTC and NTC thermistors, thermostats and thermal cut-outs,
thermal fuses and circuit protection devices are all
available from the UK's market leaders.
ATC Semitec Products
Ceramic PTC thermistors can be used as re-settable fuses. Over-voltage and over-current conditions can cause the PTC to "switch" from a low resistance into a high resistance state. This limits the through current and thus protects the circuit or load in series with the PTC thermistor.
270V Ceramic PTC Fuses - 
PDF document
Semifuse Polymer PTCs - • More info on the PTC Fuses page
A full range of motor protection PTC thermistors with switch points from 60°C to 190°C in 10K steps. Colour-coded 26AWG PTFE leads ensure compliance to DIN44081 with 3-phase triplet versions (DIN44082) and other lead-wire/mounting options also available.
Motor protection thermistors can be wired in series so that several points can be monitored at the same time - any one over-temperature condition triggering the motor protection relay.
Also a range of over-temperature PTC switches from 40°C to 100°C supplied as through-hole or ring terminals versions for heat-sink monitoring or power component protection.
Motor Protection PTCs - PDF document
PTC Thermal Sensors - PDF document
By applying a voltage across a PTC thermistor, current will flow and begin to heat the PTC. The PTC element rises in temperature until it reaches its Curie point, when its resistance will start to rise dramatically.
The increase in PTC resistance limits the through current until the PTC heater reaches a state of equilibrium. If heat is withdrawn from the PTC, its resistance will drop allowing more current to flow through the PTC until equilibrium is again reached. Conversely, if the PTC element temperature rises, its resistance will increase reducing the through current until a state of equilibrium is again achieved.
Thus a PTC thermistor can operate as a self-regulating heater.
Circular Disc PTC Elements - PDF document
Rectangular PTC Elements - PDF document
Our SKTY series linear PTC elements offer a solution for the once common KTY series.
SKTY elements are mounted on a small 3mm x 6mm p.c.b. and are available with R25 values of 1kohm and 2kohm with +/-1% tolerances.
• More info on the Platinum Sensor/Linear PTC page