In its most basic form, circuit protection is the intentional incorporation of a “weak link” in an electrical circuit. This link is usually broken when an electrical fault takes place, whether it occurs from high temperature, excessive current, or a short circuit in a conductor. Essentially, circuit protection protects the electrical circuit from damage.
Why Is Circuit Protection Important?
Circuit protective devices are important as they ensure that under fault conditions, a high fault current does not flow. This protects consumers from being injured or killed due to an electrical fault. Overcurrent protection is typically provided by circuit breakers or fuses that operate within specific limits, and they automatically disconnect the electrical supply when there is an overload or fault current, which is either a short circuit or earth fault.
Generally, overcurrent conditions develop from overloads or short circuits. Meanwhile, an overload happens because of a faulty item or multiple faulty items being connected to a circuit. A short circuit, on the other hand, occurs when a live conductor comes in contact with an exposed conductive part or another conductor in the circuit where there is low or negligible impedance. This can happen as a result of incorrectly connected wiring or damaged cables
With regard to earth faults, they are similar to short circuits and occur when a live conductor comes in contact with an earthed conductor’s exposed conductive part. Furthermore, there does not need to be a high current flow in an earth fault for this to happen. To ensure a safe electrical installation, the appropriate circuit protection devices must be present.
Types of Circuit Protection
As we mentioned, there are various types of circuit protective devices, some of which we will cover in more detail.
A fuse contains a strand of wire that melts easily, such that if a high current flows through the fuse, the wire heats up until it melts and breaks the circuit. There are several types of fuses, those of which include BS3036 rewirable fuses, BS1361/1362 cartridge fuses, and BS88 High Breaking Capacity Fuses (HBC).
? BS3036 rewirable fuses are utilized in domestic circuit protection, and they are cost effective, easily repaired, and easily maintained. Unfortunately, they are not precise, contain dangerously hot metal, and can become quickly damaged by fitting an incompatible fuse wire.
? BS1361/1362 cartridge fuses are used in plug tops and distributions as they are relatively accurate, possess a low fusing factor, can be easily replaced, and do not have any external arcing. However, they have higher price points, and it is hard to determine if they have blown.
? BS88 High Breaking Capacity Fuses (HBC) are found in industrial installation and motor circuits. More than that, they operate quickly and accurately, but they are expensive to replace.
Residual Current Device (RCD)
A Residual Current Device (RCD) is designed to detect and disconnect supply when an earth fault occurs. Common examples include when a live conductor touches an earthed equipment case, or if a live conductor is cut through.
Miniature Circuit Breaker (MCB)
A circuit breaker acts as a switch and opens when excessive current flows in a circuit. It can also be reset without damage, and the main contacts are kept closed via a latching mechanism. Please note that the latch can be tripped in two ways: thermally and magnetically.
A Miniature Circuit Breaker (MCB) is defined as an electromechanical device designed to protect an electric circuit from overcurrent. MCBs are reusable, whereas fuses are not. Due to their ON/OFF switching for circuit isolation, they are easier to use. As an added benefit, the conductors are housed within a plastic casing, meaning that they are safer to use.
Residual Current Breaker with Overcurrent (RCBO)
A residual current breaker with overcurrent (RCBO) is best suited for applications where the protection against both types of overcurrents and earth leakage current faults is necessary.
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