Shop Arrow's wide selection of unspecified electric power distribution and protection components from leading manufacturers. Sort by specification and supplier to find the right component. 1 day shipping available. Circuit Protection is required when changing conditions can lead to damage of devices and to ensure the safety of users. Circuit protection can be a mandatory requirement of sale of electronic products, depending upon the application. Devices that provide circuit protection include: circuit breakers, switches, fuses, transformers, current limiters, surge suppression, ESD protection, thermal cutoffs and brownout protection. There are also devices that isolate power supplies if the DC power supply connection is accidentally reversed.

Circuit breakers are required on mains power supply inputs in order to isolate a circuit from a high voltage source. Circuit breakers can be manual switches or they can be based upon current levels, ensuring that a device does not draw more power than the source is specified to be able to supply (as could happen in a fault condition). They can also sense leakage currents or current balance through sensing voltage or using balanced transformer circuits. Such devices are used to detect earth or ground faults.

Isolating transformers electrically isolate the primary side supply from the secondary by providing galvanic isolation. Galvanic isolation is used to prevent current flow directly between the primary and secondary transformer winding circuits, and ensures the current flowing in the protected secondary circuit cannot accidentally flow to ground through a person’s body. Isolating transformers will have a continuous power rating and an isolation rating (measured in kV).

Switches can be essential protection devices. Many products require a user to physically depress a button for the machine to operate, ensuring they are safely out of harm’s way when the machine turns on. Safety cutout switches are commonplace in workshops for rapid power down in emergency. Fuses are available as thermal fast or slow blow types. Slow blow fuses purposefully take time to break in order to accommodate for the transient inrush currents normal with some devices on power up. Resettable trip fuses are also available. Fuses are typically rated with current required to cause the fuse to break open.

NTC thermistors are available for circuits that require ‘inrush current limiting’. This can be required on devices with high capacitive or inductive load switching, and can be a common power-up or start-up problem. Resistance dynamically changes with current, and power associated with the devices I²R losses is dissipated as heat. They are usually rated for a maximum voltage potential in a series configuration, maximum power dissipation and recovery time.

Surge suppressors are non-linear devices that are high impedance until a breakdown voltage is reached and then transition to low impedance. They are used to shunt high voltage spikes in power supplies caused by any number of external effects including lightening. These are typically metal oxide varistor (MOV) devices. Lower power ESD protectors are used on sensitive exposed ports of devices to suppress (by current shunting) high voltage spikes caused by electrostatic discharge. They typically have extremely fast breakdown times measured in picoseconds. Current clamps based upon zener diode technology are used to ensure that power lines or signals do not go over voltage – leading to latch up conditions in semiconductor devices that cause damage. It is an important consideration in systems that have hot swapping or hot plugging requirements. 

Thermal cutouts are devices that sense temperature and switch off supply if the temperature has been exceeded. This prevents electronic devices from overheating. An important consideration in power supply design is protecting a circuit with under voltage situations (brownout). It is common in power supply failure for the mains power supply to drop below the minimum voltage for periods of time due to fault conditions. Should this happen, damage can occur in switch-mode power supplies and sensitive equipment (like compressors).  Control devices are available for monitoring the voltage level on the mains supply and ensuring that it is in the correct range.

There are special MOSFET based switches that can be placed in series with DC power supplies that detect supply voltage reversal and isolate the downstream circuit. This is an important feature to consider in prototyping or designing kitset products where this can be an easy mistake to make.