As modern industry develops, electricity becomes incredibly useful, but it also becomes incredibly dangerous too! Do you know that it only takes a few milliseconds for a strong electrical current to flow through your heart to hurt you?
Think about this, if you are using an electric cutter and you accidentally cut the cord, if the tool has a metal casing, you are grasping it, or you are repairing the circuit and you accidentally touch the bare cord, and you are standing on the ground, the electricity has to go somewhere. There is a very high risk that your body will form a “short circuit,” the path of least resistance for current to flow.
It only takes the blink of an eye for a stream that is doing you a favor, change your mind and pass through your body.
So how do we avoid electricity through our body? One way to reduce the risk is to use a smart protection device called a residual current device (RCD) or residual current circuit breaker (RCCB).
This is a device that instantly breaks an electrical circuit to prevent serious damage from an ongoing electrical shock.
In Europe, these are better known by their initials RCD, and an RCD + MCB (Miniature Circuit Breaker) is known as a Residual Current Circuit Breaker (RCBO) with over-current protection.
In the United States, the device is more commonly known as a ground fault circuit interrupter (GFCI), ground fault interrupter (GFI), or a leakage current interrupter (ALCI).
In Australia, they are sometimes known as safety switches or an RCD. An earth leakage breaker (ELCB) can be a residual current device, although there is also an older type of voltage operated earth leakage breaker.
How are people electrocuted?
Figures vary from year to year for each country, but global statistics reveal that electrocution is one of the top five causes of death at work.There are many electrical shock accidents in the home, and electrical accidents cause several hundred deaths and several thousand injuries each year in a single country.
How and why do people get an electric shock?
Essentially, as leakage current equipment is accidentally touched or when an electrical appliance fails in such a way that its exposed metal parts temporarily become conductive and dangerous. Many appliances have fuses to protect against excessive currents, but it does not help in the leakage current situation. Some appliances also have “ground” or “ground” wires to protect us when the wires touch things they shouldn’t.
The “ground” or “ground” is not part of the normal power circuit, it is just a replacement wire connected to the exposed metal parts of an appliance. It eventually connects to the ground through your home wiring, then through a metal spike or water pipe that enters the ground outside your home.
The basic idea is that if the live wire fails and touches something like the metal outer casing of a toaster, then the metal distribution box, the ground wire carries the current safely. But what if the ground / ground wire fails the same way? The circuit will pass through your body, how to protect yourself against electric shock? That is where RCD, GFCI, ELCB come to our rescue.
How do RCD devices work?
The RCD consists of five parts, there is a Magnetic Relay (1), Mechanism (2), Input Line Terminals (3), Load Terminals (4), and Sense Coil (5).
The active wire connects the incoming line terminal (1) and connects to your electrical appliances from the load terminals (4), to turn on the mechanism handle (2), to make the connection of copper contact parts of the incoming line terminals (3) and the sense coil (5).
The sense coil is a residual current transformer that surrounds (but is not electrically connected) the active and neutral conductors. In normal operation, all current downstream of the live conductor returns to the neutral conductor. The currents in the two conductors are therefore equal and opposite and cancel each other out.
Any fault in the ground (for example, caused by a person touching a live component in the connected device) causes some of the current to take a different return path.
This means that there is an imbalance (difference) in the current in the two conductors (single-phase case), or more generally, a non-zero sum of currents between several conductors (for example, three phase conductors and a neutral conductor). This difference causes a current in the detection coil (5), which is picked up by the magnetic relay (1).
The sensing circuitry then removes power from the mechanism (2) and the input line terminal contacts (3) are forced apart by a spring, cutting off the supply of electricity to the apparatus.
The RCD is designed so that current is interrupted within milliseconds, greatly reducing the chances of a dangerous electrical shock being received.
Who Invented the RCD / ELCB / GFCI?
He was the electrical engineer Charles Dalziel (1904-1986) from the USA. He served as professor of electrical engineering and computer science at the University of Berkeley.
He saved countless lives when he came up with the brilliant idea of the ground fault circuit interrupter around 1960. He began patenting the idea in January 1961 (in application number 85,364) and finally obtained a patent in October 1965. Among the Benefits of Dalziel’s invention are high enough current sensitivity to protect people from electrocution, low operating current, and power consumption.
Do you need to buy an RCD / ELCB / GFCI?
In our modern household consumer unit (switchboards), like the image shown below, RCDs have been incorporated into some (but not all) domestic circuits.
This means that if you accidentally cut a wire or get it wet, the trip switch on the consumer unit will interrupt power and save your life by doing the same work as a plug-in RCD. It is vitally important to understand how your consumer unit is configured. In this chart.
For example, only the outlets above have RCD protection. So if you’re using an overhead plug to power your toaster, you’re protected. However, if you were using power tools plugged into a downstairs outlet, you would need to use a plug-in RCD for protection because the upstairs circuits do not have RCDs attached.