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Electricity – Part 1 Peter Coulahan Learning Outcomes Having completed all of the learning activities associated with this lecture, you should be able to: Electricity – Part 1 Dr Peter Coulahan University College Dublin Safety Officer Explain the basic principles of electricity in the context of its relevance to the safety of persons at work Explain the conditions / factors that must be present for a person to suffer an electric shock Explain the key terminology associated with electrical safety Describe the physiological effects of electric shock and the associated risks Detail the arrangements that can be put into place to mitigate the risks of electric shock and electrical fire. What is electricity? Terminology – voltage, current, resistance, earth, Ohms Law, electrical circuits, short circuit, direct current (DC), alternating current (AC), static electricity, electrical arcing Electricity is at its simplest the flow of electrons through a material Like charges repel each other whilst opposite charges attract – if you try and force electrons together they will repel each other and flow to a positively charged area or to an area with no charge, i.e. earth Electricity Part 1 Part 1 An introduction to electricity Part 2 Practical electrical safety measures What is electricity? Structure of a carbon atom Electron / Electricity Flow 6 protons + 6 neutrons Electron Proton Neutron Carbon atom 1 Electricity – Part 1 Peter Coulahan Electron / Electricity Flow Voltage The movement of negatively charged electrons to a positively charged area or to an area with no charge (i.e. earth) is the basic principle Voltage is a measure of the force which motivates electrons / electricity to flow behind electricity For electricity to flow between two points there must be a ‘voltage difference’ between those two points Electrons will always take the path of least Voltage is measured in volts Resistance is a measure of a materials ability to either impede or allow the flow of electricity Conductors allow electricity to flow easily – they exhibit low resistance Insulators do not allow electricity to flow easily – they exhibit a high resistance Resistance is measured in Ohms (Ω) An electrical circuit is a closed path through resistance to earth Current Current is a measure of the amount of Resistance electricity flowing in a circuit It is measured in amps or milliamps The term amperage is sometimes used interchangeably with current Ohm’s Law There is a fixed relationship between voltage, Electrical Circuit current and resistance This is known as Ohm’s Law which electrical current can flow An electrical circuit can be disrupted by Voltage = Current x Resistance breaking the pathway at any point along its Current = Voltage / Resistance route Resistance = Voltage / Current A short circuit occurs when electricity is lost from the closed pathway 2 Electricity – Part 1 Peter Coulahan Alternating Current (AC) – Domestic Supply Direct Current (DC) Electron flow + Battery RMS Average 230 Volts Voltage Electric lamp (glowing) Time - Electron flow One Cycle 1/50 sec (50 Hz) The flow of electricity in the same direction through a circuit at a constant and steady voltage. Alternating Current (AC) Three Phase Alternating Current In an alternating current electricity is supplied at a constantly changing voltage and direction When referring to AC voltages we refer to the Root Mean Square of the supply, i.e. the average voltage of the supply The number of cycles per second is known as the frequency of supply Three phases Voltage Time Static Electricity When two materials are brought into contact with each other electrons can be transferred from one to another giving the latter a negative charge If a static charge is allowed to build up on a material then when a conductor is brought close to the affected area a spark can jump from one to the other – static discharge Electrical Arcing An electrical arc is a discharge of electricity between two or more conductors across a gap, e.g. as when electrical current ‘jumps’ from a high voltage power line across an empty space to a metal digger located below It differs from static discharge in that no contact between materials is required 3 Electricity – Part 1 Peter Coulahan Summary What is electricity? Voltage Current Resistance Ohms Law Electrical circuits Earth Direct current (DC) Alternating current (AC) Static electricity Electrical arcing Electricity Part 1 An introduction to electricity Part 2 Practical electrical safety measures 4