Current is the flow of electrical energy and is measured in AMPS
Voltage is the force or pressure that pushes current around a circuit and is measured in VOLTS
The public utility supply voltage in the UK is 230V
Voltage is measured between two points and the two points of an 230V electrical supply are Live (L) and Neutral (N). The cables are coloured Live – BROWN and Neutral – BLUE
When current flows heat is produced and whether this heat is wanted or not it has to be dispersed. Failure to disperse this heat with cause components to overheat and fail but more importantly could cause a fire. Fuses and Circuit Breakers are used to stop too much current flowing and therefore prevent fires.
The opposition to the flow of current is RESISTANCE and is measured in the units of OHMS (Ω). It is this resistance in conjunction with the current that causes heat to be produced. The resistance of a component is determined by the material it is made out of, its length and its cross sectional area.The bigger a component is then it will have less resistance. Therefore when more current needs to flow components have to be bigger. A component that is too small could potentially overheat and catch fire.
The current flowing through a component is determined by the VOLTAGE divided by the RESISTANCE.
Electric shock is when current flows through a person. The current flowing through the person would be determined by the voltage and the resistance of the circuit that the person makes. This person would therefore have to come into contact with a live component and the person has to make to two points of contact in order for current to flow through the. One point of contact a person might be making anyway is the ground. This means that a person has to only make one point of contact with a live source and the ground is automatically the second point of contact. Wearing good rubber soiled shoes or standing on rubber mats would effectively (electrically) disconnect a person from the ground. The rubber will be adding resistance into the circuit. This would help minimise the risk of shock. However if a person makes two points of contact with two other parts of the body then the rubber soled shoes would be of no help.
It is not possible to know in advance how much current will flow through a person when they touch a live source. It is variable and unpredictable. It all depends on the person and the circumstances of how they got that shock. A wet environment would be more hazardous than a dry one as this may lower the resistance of the circuit that the person has made.
The current though a person is determined by the voltage and the higher the voltage is then; the more likely it is that a person is going to be hurt, injured or killed. If a person comes into contact with 230V IT IS POSSIBLE that enough current could flow through the person to harm them. Therefore 230V should be considered as a potential killer. Voltages up to 50V are unlikely to hurt a person.
The consequences of electrical shock might vary from an unpleasant experience, aches and pains, burns and effects on the heart. A current of only 100mA (0.1A) could cause the heart to go into Ventricular Fibrillation (no heart beat) and if that is not rectified very soon a person may suffer serious injuries or death. When we work on equipment we always remove the power source and make sure no-one can inadvertently reconnect that equipment to the supply.
These regulations are a statutory requirement meaning they have to be complied with as they are a legal requirement.
These regulation makes statement such as
Many electrical systems store energy and this could create a danger in some cases. Batteries are often inside systems but these are low voltages and would not be harmful in terms of electric shock. However a person should be very careful not to allow, say, a screwdriver to touch across the terminal of the battery creating a very low resistance path. Making a low resistance path across an electrical supply is known as a short circuit. This could cause a high current and the battery could overheat and potentially catch fire.
One possible problem that could occur with an electrical system is that the outer metal case could become live due to a connection between the live and the casing. This would give an electric shock to the user of the equipment. An earth wire, colour Green and Yellow, is connected to the casing of the equipment. If a short circuit to the casing occurs, this creates a low resistance path, causing lots of current to flow which should blow a fuse or trip a breaker. Items of equipment such as chargers, some domestic appliances do not have a metal casing (the casing is made of plastic) and therefore do not need an earth.
An RCD (Residual Current Device) measures the current flowing into a circuit and compares it with the current flowing out of the circuit. If these two currents are different it means that current is flowing somewhere it shouldn’t be flowing. This will typically be though a person or through the body of a piece of equipment. RCDs will not allow the difference between the current in the live differ from the current in the neutral by more than 30mA. This will hopeful protect a person from harmful electric shock.
