A Residual Current Device (RCD) detects current imbalances in single and three-phase circuits, cutting off power if necessary. It also acts as an insulation monitoring device and can detect unwanted arcing in electrical wiring.
A residual current device is a protective agent that detects any imbalance of the currents in single and three-phase circuits and cuts off the power if necessary. Detects the sum of the electric current to the mains conductors as opposite vectors with the same magnitudes. For single-phase connections, the relevant connections are the live wire and the neutral wire. The current flowing through the live wire must be the same as the current flowing in the neutral wire. If not, problems in the circuit must be fixed or lives could be in danger.
Usually the residual current device for single-phase protection makes use of the inductive coupling of the currents induced by the network of the phase and neutral conductors. The latter must be zero if the wiring and insulation are perfect. There are several scenarios where the active and neutral current will have a difference.
In a simple single-phase connection, if the load draws 5 Amperes (A), the current on the live wire and the electric current to the neutral should be 5 A. If the RCD is connected, it will be able to sense up to 20 milliamperes (mA ) in the difference in electric current between the two wires. This could mean that a person has accidentally touched the live wire and is electrocuted by the current in the ground. If this person touched the live wire with bare feet to earth, the Residual Current Device (RCCB) will detect this, break the circuit, and save the person from further electric shock. In this type of usage, the RCCB may also be referred to as an earth fault circuit breaker or earth fault interrupter where the earth fault could be a leakage current caused by poor insulation, water ingress or possible lightning strike of a person.
Furthermore, the RCD is also an insulation monitoring device. When the insulation of the wiring is live or the neutral has been damaged exposing the wire, there is the possibility of leakage to earth or elsewhere. Leakage current goes to an unintended location, so the RCD will detect it and the RCCB will trip the breaker and de-energize the load. Some RCDs such as the appliance leakage current breaker are designed to protect appliances that may have insulation problems or contamination.
The arc fault circuit interrupter (AFCI) is an electrical wiring device that detects and stops unwanted arcing in electrical wiring. These optoelectric arcs are usually caused by loose connections that begin with a very low power arc and progress to a higher power arc that generates enough heat to start a fire. AFCI can detect electrical burst patterns associated with an arc and de-energizes the circuit by breaking it.
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