Circuit Protection Devices

www.shallin.com

Description:

The glass fuse is a type of sacrificial overcurrent protection device. Its essential component is a metal wire or strip that melts when too much current flows, which interrupts the circuit in which it is connected. Short circuit, overload or device failure is often the reason for excessive current. Fuses are selected to allow passage of normal current and of excessive current only for short periods.

Important performance ratings to consider when specifying fuses include voltage rating, current rating, rated braking capacity, and interrupt rating.

• The voltage rating of the fuse = the maximum voltage up to which a safe fault current interruption will occur
• The rated current of the fuse should consider the maximum continuous operating current of the circuit and the influence of the ambient temperature
• The rated breaking capacity of the fuse (interrupting rating) = the short circuit current at which the fuse can blow (at the rated voltage) without destruction or arcing being maintained
• Interrupt ratings can be high interrupt, medium interrupt, or low interrupt

There are two types of fuses:

1. Quick-Acting Fuses are typically used in circuits with small inrush currents or where overcurrent or short circuit must be quickly interrupted, such as resistive loads.
2. Time-Delay fuses are used where high starting inrush currents will occur and decay gradually, such as inductive or capacitive loads.

Maamoon Est. for Electrical Engineering offers the 20 and 30 mm in diameter.

www.shallin.com

Description:

Fuse holders are devices for containing, protecting and mounting fuses. Fuse holders come in two basic types, open or fully enclosed.

Maamoon Est. for Electrical Engineering offers the open fuse holder type such as fuse clips, and fuse blocks. Also, we offer the fully enclosed type such as panel mount, and in-line mount.

www.setfuse.com

Description:

PTC (Polymeric Temperature Coefficient) Resettable Fuses are unlike traditional fuses that have to be replaced after a fault condition, this may not be necessary when using resettable fuses. The internal resistance of the component increases in response to an overcurrent or a short-circuit condition, limiting subsequent disturbances.

After the fault condition is removed, the device cools and the internal resistance drops to nearly its initial value, permitting normal equipment operation to resume.

Maamoon Est. for Electrical Engineering offers the 20, 25, and 30 mm in diameter.

www.setfuse.com

Description:

Thermal cutoffs are a nonresetting, thermally-sensitive devices that are designed to protect electrical appliances and industrial equipment from fire. They are sometimes called thermal one-shot fuses. When ambient temperature is increased to an abnormal level, the thermal cutoff senses the temperature change and breaks the electrical circuit. This is accomplished when an internal organic pellet experiences a phase change, allowing spring-activated contacts to permanently open the circuit. Consequently, cutoff temperature is one of the most important specifications to consider when selecting thermal cutoffs and thermal protectors.

Maamoon Est. for Electrical Engineering offers ...

www.setfuse.com

Description:

Thermistors are thermally-sensitive devices whose electrical resistance varies with temperature. There are two main types of thermistors:

1. Positive Temperature Coefficient (PTC) where electrical resistance increases as temperature rises.
2. Negative Temperature Coefficient (NTC) where resistance drops in a nonlinear manner with a rise in temperature.

Maamoon Est. for Electrical Engineering offers ...

www.setfuse.com

Description:

Metal Oxide Varistors (MOVs) are semiconductors that protect electronic components and systems from transient voltages. These clamping devices contain a matrix of zinc oxide grains sandwiched between two metal plates which serve as electrodes. The boundaries between grains form diode junctions which allow current to flow in only one direction. Applying low or moderate voltages causes reverse leakage through the diode junctions and a small flow of current. Higher voltages trigger the avalanche effect and cause the diode junctions to break down. As a rule, metal oxide varistors exhibit highly non-linear current-voltage characteristics. They have high resistance at low voltages and a low resistance at high voltages.

Maamoon Est. for Electrical Engineering offers ...