S05 Presentation - Earthing PDF

UEENEEG063A S05 - Earthing PRESENTED BY EARTHING UEENEEG063 Control & Protection of Circuits Section 5 REGULATIONS Different levels of regulations AS/NZS 3000:2018 SIR of NSW October 2019 Annexure Metering Requirements July 2018 Electricity Supply Standards – Ausgrid TAFE NSW EARTHING...

UEENEEG063A S05 - Earthing PRESENTED BY EARTHING UEENEEG063 Control & Protection of Circuits Section 5 REGULATIONS Different levels of regulations AS/NZS 3000:2018 SIR of NSW October 2019 Annexure Metering Requirements July 2018 Electricity Supply Standards – Ausgrid TAFE NSW EARTHING - INTRODUCTION Without exception the earth is the most important conductor of any electrical installation An effective earth ensures personnel safety and equipment protection particularly during fault conditions Section 5 of the wiring rules deals comprehensively with earthing arrangements and earthing conductors TAFE NSW EARTHING TERMS Readily Accessible >2.0m from ground Earthed – equipment or conducted to general mass of earth Earthed situation – any situation where someone can touch exposed conductive parts while being in contact with the earth All definitions to terms used in AS3000 are in Section 1.4 in alphabetical order Take the time now to find section 1.4 (Definitions) and highlight it. You should also put a page tab to make it easier to find next time. TAFE NSW GENERAL MASS OF EARTH The term ‘earth’ refers to the general mass of ground or soil The voltages referred to in electrical systems relates to the general mass of earth Earth therefore is the reference point, or zero potential point, to which all other voltages refer TAFE NSW REASONS FOR EARTHING Fundamental reason for earthing To ensure exposed conductive parts do not become live under fault conditions TAFE NSW GENERAL MASS OF EARTH When you are standing on ground, your body is at approximately the same voltage potential of earth (whatever that voltage is – generally zero) In an installation when all accessible metal is connected to earth then these are also at ground potential TAFE NSW AS 3000 EARTHING TERMS The Wiring Rules uses terms for conductive parts in an installation; AND conductive parts that aren’t part of the installation, but may come into contact with the conductive parts of the installation The terms used are Exposed Conductive Parts and Extraneous Conductive Parts TAFE NSW EXPOSED CONDUCTIVE PART The wiring rules specifies the term for an exposed conductive part In general terms it is any metal part of an electrical system that can be touched and may become live in the event of a fault (insulation failure) TAFE NSW EXPOSED CONDUCTIVE PART Exposed conductive parts are conductive parts of electrical equipment that is not live, but can become live if basic insulation fails TAFE NSW EARTHING OF ELECTRICAL EQUIPMENT Exposed conductive parts are required to be earthed when they are installed or could operate in an earthed situation There are exceptions when they do not need to be earthed such as double insulation and ELV The Wiring Rules stipulate earthing of specific equipment such as lighting points and socket outlets TAFE NSW 13 CLASS OF EQUIPMENT Equipment is classified according to its protection method: Class 1 equipment – Earthed Class 2 equipment – Double insulated Class 3 equipment – Extra Low Voltage TAFE NSW G063 SECTION 1 - SAFETY PRINCIPLES EXTRANEOUS CONDUCTIVE PART Is a conductive part that is not part of the electrical installation but may be at a different potential to the earthing system. Examples of extraneous conductive parts include the following: (a) Metal waste, water or gas pipe from outside. (b) Cooling or heating system parts. (c) Metal or reinforced concrete building components. (d) Steel-framed structure. (e) Floors and walls of reinforced concrete without further surface treatment. (f) Tiled surfaces, conductive wall coverings. (g) Conductive fittings in washrooms, bathrooms, lavatories, toilets, etc. (h) Metallized papers. TAFE NSW Extraneous conductive parts are conductive parts that DO NOT form part of the electrical installation, but may be at the electrical potential of a local earth EXTRANEOUS CONDUCTIVE PART TAFE NSW  EQUIPOTENTIAL BONDING Equipotential bonding is a system that connects an earth cable to an extraneous conductive part This is done by connecting the bonding conductor to the earthing system of the installation (The earth bar or terminal) Its job is to ensure that any potential on the extraneous part is at the same potential as the exposed conductive parts of the electrical installation TAFE NSW EQUIPOTENTIAL BONDING Dangerous potentials may be present on these extraneous parts under circumstances such as Distribution system load current flowing in the soil Lightning discharges A fault external to the building Telecommunication voltages on equipment TAFE NSW  EQUIPOTENTIAL BONDING Extraneous conductive parts that need to be bonded: Conductive water pipes Steel building frames Other conductive piping such as fire sprinklers Conductive reinforcing of floors under showers and bathrooms Exposed conductive parts in swimming pool zones Telecommunication earthing system TAFE NSW EQUIPOTENTIAL BONDING The Wiring Rules stipulates the type of conductors and their size to be used It also stipulates other specific requirements Take the time now to find Equipotential bonding section and highlight it. You should also put a page tab to help you get back to this section TAFE NSW EARTH STAR DISTRIBUTION SYSTEM Most common way to distribute power is by four-wire secondary distribution transformer To create a zero reference point, the neutral star point of transformer is solidly connected to general mass of earth TAFE NSW EARTH STAR DISTRIBUTION SYSTEM Earthing the neutral of the transformer ensures primary voltages cannot be applied to low voltage installations if a breakdown of insulation occurs – protection fuses would blow This type of fault (short-circuit) would apply a high voltage to the installation casing insulation failure and subsequent fires TAFE NSW EARTH STAR DISTRIBUTION SYSTEM - ADVANTAGES Common earth reference between distribution transformer neutral and consumer’s earthed equipment Provides for voltage stability. With the earthed star point, the vector sum of three phase currents is nullified to zero. Without earth, a s/c fault will cause neutral to rise in potential through transformer windings Provides for 2 supplies, 400v & 230v supply Phase to earth faults cause the protection fuses to blow TAFE NSW MAIN EARTHING CONDUCTOR Conductor connecting the main earth terminal / connection or bar to the earth electrode Size of main earth is determined from T5.1, relating to the size of the largest active conductor Minimum size is 4mm2 TAFE NSW MAIN EARTH RESISTANCE Locate and highlight the two clauses in the wiring rules that indicate the maximum value of resistance for the main earth (One in S5, one in S8) Note that the test should include the connection to the earth electrode and terminal / connection or bar TAFE NSW MEASURING RESISTANCE OF MAIN EARTHING CONDUCTOR TAFE NSW MAIN EARTH TERMINAL / CONNECTION OR BAR In every installation a main earthing terminal / connection or bar shall be provided at the main switchboard. Cl. 5.3.4 The following conductors shall be connected Protective Earth Conductor Main Earth MEN Equipotential bonding conductors Functional earth conductors TAFE NSW  EARTH SIZES Table 5.1 is used to determine all earth sizes. Make sure Table 5.1 is highlighted and page tabbed. You will use this many times again! Exceptions however include: MEN – when have unprotected or single insulated consumer mains (5.3.5.2) Exposed conductive parts associated with unprotected consumer mains (5.5.3.5) Equipotential Bonding conductor (5.6.3.2) Main earth – limitations (5.3.3.2) FSC earth – limitations (5.3.3.4 a) You may want to note these exceptions next to Table 5.1 (MEN and Unprotected Consumer mains expanded later in presentation) TAFE NSW 28 TABLE 5.1 TAFE NSW  EARTH ELECTRODE The purpose of the earth electrode is to connect earthed parts of electrical installation to the general mass of earth This will allow multiple paths for fault current to clear a fault All wiring systems connected to it will be at zero potential or in the case of an earth fault, at a value above zero depending on the voltage drop over the fault The types of electrodes should be one of the types described in Cl 5.3.6.2 Copper clad rod type electrodes must be driven to a depth of 1.2m TAFE NSW EARTH ELECTRODE Electrode must be located in moist soil. Cl.5.3.6.4 Connection must be accessible, with adequate conductivity. Cl. 5.5.1.2 The connection needs to have protection from corrosion and against mechanical damage. Cl. 5.5.1.2 The P.V.C. pipe in this photo is to allow water to enter the electrode area TAFE NSW  MULTIPLE EARTHED NEUTRAL The MEN system of earthing is where the distribution neutral is used as a low resistance path for earth fault currents It carries any fault current as a result of an active conductor passing current to earth TAFE NSW M.E.N. Stands for Multiple Earthed Neutral A system where all earthed parts of electrical installation are connected together, to the general mass of earth and the supply neutral The M.E.N. link connects the earthing system to the supply neutral AS3000 outlines connection and size details. Cl. 5.3.5 NSW SIR 1.17.7 advises cannot be connected to supply neutral link TAFE NSW  MULTIPLE EARTHED NEUTRAL The neutral conductor is connected to earth at the distribution transformer, at each consumer’s installation and at specified poles or underground pillars A timber batten covers the grounding conductor to provide mechanical protection and also protects against ‘touch potentials’ when a fault current is flowing TAFE NSW MULTIPLE EARTHED NEUTRAL The ground serves to cancel out the effects of leaking currents in an installation by earthing out, or reducing to a zero potential, the voltages picked up by earth conductors The number of parallel paths the fault current can access assists the flow of current TAFE NSW  MULTIPLE EARTHED NEUTRAL A properly earthed installation provides protection for persons and animals against the danger of electric shock by ensuring electrical isolation of any defective equipment through the operation of protective devices TAFE NSW  MULTIPLE EARTHED NEUTRAL With the MEN system, if the circuit neutral is disconnected or suffers a high resistance fault, the fault current can flow through the earth conductor back to the main switchboard However this alone is insufficient for personnel safety. If the distribution neutral becomes open circuit, the only path for fault current is through the ground This path under dry conditions can be a high impedance, resulting in touch voltage potentials between the earthing system and exposed conductive parts of electrical system The effectiveness of the MEN system relies on the continuity of the neutral conductor, the MEN link and the connection of the main earthing conductor to the earth electrode. TAFE NSW  SCENARIO A neutral connection in the service mains somewhere has a hot joint. The returning current will always look for the path of least resistance. Given the fault in the neutral, some of the current will follow a parallel path and travel through the distribution earthing system (Through the ground) As fault current flows through the ground a voltage drop occurs due to the impedance of the earth Therefore different parts of the earth can be at different voltages TAFE NSW EXTRANEOUS CONDUCTIVE PART How does this different potential of the earth cause problems Say a shower head and tap is connected by metallic pipe throughout the house and this pipe enters the house on the opposite side to where the bathroom is. When you stand in the shower you are standing on the wet floor which has an earth connection in the concrete floor (the reinforcement in the concrete is connected to earth). Now you touch the shower head or tap which is at the potential of the earth on the opposite side of the house What you are doing is touching different parts of the earth, which might be 20 or more metres apart. And if fault current is flowing in the earth, you can get electrocuted. TAFE NSW  EQUIPOTENTIAL BONDING Remember the equipotential bonding conductor. It’s job is to ensure that any potential on the extraneous part (taps and shower head) is at the same potential as the earth and exposed conductive parts of the electrical installation. TAFE NSW DETERMINING SIZE OF M.E.N. TAFE NSW PROTECTIVE EARTHING CONDUCTORS A PEC is an earth that connects the earthing system to the electrical installation (But not the Main Earth or Bonding conductors) All PEC’s must be directly connected to the main earth, the earth terminal at a switchboard or another PEC The symbol for a PEC is shown on the right TAFE NSW  PROTECTIVE EARTHING CONDUCTORS PEC conductors may be Separate conductor with g/y insulation An earth conductor in a sheathed cable Metallic sheaths, armours and screens of cables Conductive cable enclosures (conduit, trunking etc) Conductive framework Catenary wires TAFE NSW PROTECTIVE EARTHING CONDUCTORS The purpose of the PEC is to provide a safe path for earth fault current, to ensure the protective device operates The minimum size of the PEC is determined with respect to the CSA of the associated active conductor, from Table 5.1 The earth conductor fixed to metal frame of a switchboard is a PEC, not a bonding conductor If it is a main switchboard, with unprotected consumer mains, the size of the PEC should be at least the same size as the neutral conductor (same CCC) Find this clause together and highlight it now..5.5.3.5 TAFE NSW DETERMINING SIZE OF PEC FOR MAIN SWITCHBOARD TAFE NSW EXAMPLES OF EARTHING ARRANGEMENTS USING EARTH BAR /TREE ARRANGEMENT TAFE NSW  FUNCTIONAL EARTHING CONDUCTORS Functional earthing refers to the need for certain points in electrical equipment or systems to be connected to the earthing system in order to maintain their proper function The symbol for functional earth terminals is shown on the right TAFE NSW FUNCTIONAL EARTHING CONDUCTORS Some RCD have a functional earthing conductor coloured white or pink This is used for the operation of the RCD if the neutral is disconnected Functional earthing conductors do not perform a safety function and are not considered part of the earthing system TAFE NSW EARTHING IN OUTBUILDINGS Clause 5.5.3.1 Can connect to main earthing systems via earthing cable Or, can wire a separate MEN system in the outbuilding Ensure there are no parallel paths from conductive water pipes, covered walkways etc. Equipotential bonding connection should be at ONE END only. TAFE NSW EARTHING IN OUTBUILDINGS TAFE NSW 50 EARTH FAULT LOOP The earth fault loop is shown on the right. It is vital that this path has a low impedance allowing the fault to be cleared within the required time. (Ensuring touch voltages are not present) Wiring rules outline the impedance requirements for the fault loop. TAFE NSW 51 THE END TAFE NSW PRESENTATION TITLE TO GO HERE