Electrical Workplace Safety

Transcription

1 Electrical Workplace Safety Alan Kelly 23 rd September 2015

2 Objectives To provide an understanding of Electrical terms and the concepts of electricity To introduce Electrical Protective Devices and provide an understanding of their use To identify the hazards associated with work on or near Live electrical equipment. To demonstrate the need for and use of Electrical Safe Operating Procedures. To Identify the Legislation associated with Electrical Work and Electrically Operated Equipment.

3 Statistics Fatal Electrical Accidents In Ireland Fatalities In 2005 there were 5 people electrocuted 2 of these fatalities were with Low Voltage (LV) = volts. In 2006 there were NO Electrical Fatalities in Ireland First time since 1936

4 What is Electricity? SO WHAT IS IT MADE OF!!! Electricity is made up of a range of components e.g. Voltage Current Resistance Power.

5 What is Electricity? Aluminium Atom 29 Electrons 13 Electrons Nucleus Electricity is the moving of Electrons in a wire or conductor and the consequence of this movement.

6 Voltage Is the pressure which pushes the electricity through the system from the Generator to the Customer. Measured in VOLTS Symbol = V 230 Volts (230V) 10kV/ 20kV /400kV Italian Physicist Alessandro Volta

7 Voltage Voltage Voltage = Pressure Measured in Volts Symbols V, U and EMF Pressure gets electrons to move Levels of Pressure 230V = level of pressure 400V = higher level of pressure 1000V = higher level again.

8 Voltage Levels Extra Low Voltage Low Voltage Medium Voltage High Voltage = < 50Volts = Volts = 1kV 38kV = 38kV- 400kV

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10 Current This is the Rate of Flow of electricity which flows through the system from the Generator to the Customer. Measured in Amps Symbol = I e.g. 20 Amps 20A 20mA (ma=1/1000a) French Physicist Andrea Ampere

11 Current Current = Movement of Electrons Current measured in Ampere s or amps Symbol = I or A

12 Types of Current DIRECT CURRENT (DC) ALTERNATING CURRENT (AC)

13 DC Direct Current CURRENT FLOWS IN ONE DIRECTION LIKE A BICYCLE CHAIN

14 AC Alternating Current CURRENT FLOWS IN BOTH DIRECTIONS LIKE A HAND SAW

15 ALTERNATING CURRENT ALLOWS THE USE OF TRANSFORMERS WHICH MAKES THE TRANSMISSION OF POWER MORE EFFICIENT

16 400 Voltage Voltage Voltage Voltage Current Current Current Ic Ic Current + Ic Current + Ic 100 Volts Time

17 Frequency Frequency of a system = Number of cycles per second In Ireland this = 50; It is measured in Hertz (Hz) 50hz

18 Stroboscopic Effect May cause rotating objects to appear stationary or at least moving slowly Fluorescent lighting Problems Solution Filament lighting adjacent to machine Solution Supply each row of lights from separate Phases

19 Effects Of Electric Current Heating Effect caused by friction Examples Kettle, Cooker, Space Heater, Immersion & Light bulb

20 Effects Of Electric Current Magnetic Effect Voltage Examples Motors, Transformers, Relays, Contactors & RCD s

21 Resistance The extent to which the Flow of Electricity is impeded in a circuit. Measured in Ohms Symbol = Ω (or R or Z) e.g. = 200 Ohms, 200 Ω, 2M Ω German Physicist Georg Ohm

22 Resistance Resistance = Opposition to current flow Resistance due to type of material & CSA Higher Resistance due to smaller CSA Measured in Ohms - Symbol = R or Ω

23 THE ### ELECTRON WON T MOVE THE ELECTRON WILL MOVE EASILY THE ELECTRON WILL MOVE, BUT WITH DIFFICULTY EASY FRICTION HEAT ATOM ATOM ATOM INSULATOR CERAMICS P.V.C. (Plastic) RUBBER OIL CONDUCTOR GOLD SILVER COPPER ALUMINIUM MERCURY RESISTOR TUNGSTEN STEEL NEON GAS SALT WATER CARBON

24 Power Is the rate at which Current flows at a given Resistance and Voltage Power = Voltage x Current Measured in Volt-amps / Watts e.g. 10 VA 15 kva /kw

25 Types of AC circuits Single Phase The transfer of electricity using Two Wires Three Phase The transfer of electricity using 3 or 4 wires.

26 Switching On of Electrical Circuit Switch PH Fuse N Fuse is in circuit to protect the conductors (wires) Switch is in circuit to control the flow of current

27 Switching Off of Electrical Circuit Switch PH Fuse N When ever current flow is interrupted you get an ARC or SPARK due to the Voltage trying to push electrons across the gap

28 Switching Off in Explosive Atmosphere The use of electricity can generate hot surfaces or sparks which can ignite an explosive atmosphere Dust Switch PH Fuse N Explosive Atmosphere = Work Areas where Dust (flour mill), Gases, Paint Spray or Vapours (Petrol Station) exist.

29 IP Rating IP rating of equipment refers to the electrical equipments ability to withstand the ingress of either liquids or solid bodies IP 56 ; In this example the Ingress protection offered by this equipment is given by the two numbers. The first number refers to the protection against the ingress of solid bodies. The second number refers to the protection against the ingress of liquid.

30 IP Rating Example of IP rating IP45 = Protection against normal dust and hosing and is suitable for Dairies. IPX4 = only protected against hosing is given

31 Electrical hazards associated with electrical systems and equipment include: Electric shock Burns sustained at the point of accidental electrical contact, or due to arcing from high voltage conductors Fires caused by overheating or ignition of explosive atmospheres Secondary injuries as a result of muscle spasms during shock or, for example, falling from a ladder after a mild shock.

32 The Electrical Circuit Live Electricity Supply Neutral Frame is Live Electrical Appliance L O A D Fau lt Main Earth Probably a FATAL accident General Mass of Earth

33 Live Electricity Supply What can be done to try to prevent the electric shock? We can Earth the appliance or machine We can install a protective device (fuse or mcb) Neutral The Electrical Circuit Fuse/mcb Electrical Appliance L O A D Fau lt Neutralising Link Main Earth Earth Rod General Mass of Earth

34 The Electrical Circuit What can be done to try to prevent the electric shock? Protective Device Operates Electrical Appliance Live Fau lt Electricity Supply L O A D Neutral Main Earth The larger current flowing blows the fuse and the appliance frame is no longer Live General Mass of Earth Earth Rod

35 The Electrical Circuit Another device used to prevent electric shock is the RCD RCD/ELCB Electrical Appliance Live Electricity Supply Fuse/mcb R E L A Y L O A D Fau lt Neutral Main Earth Earth Rod General Mass of Earth

36 In the event of an Earth Fault the RCD trips the circuit faster than the fuse/mcb Electrical RCD/ELCB Appliance Live Neutral Electricity Supply The Electrical Circuit Fuse/mcb R E L A Y Test Button L O A D Fau lt Main Earth The RCD uses the imbalance between the current in the phase and neutral to identify that there is a fault. General Mass of Earth Earth Rod

37 RCD T The test button on RCD s installed in this country are marked with the letter T It is possible to purchase Plug-in RCD s

38 Circuits feeding plugged-in appliances, showers and immersions must be protected with an RCD. Typical domestic distribution board

39 RCD Recommended to test the RCD twice a year, probably best at time change in spring & Autumn Typical tripping times expected using RCD tester = 0.30 secs at 30mA 0.15 secs at 60mA 0.04 secs at 150mA Testing regime depends on Installation

40 Working on Electrical Equipment Electrical Machine Live Electricity Supply L O A D Neutral Main Earth Probably a FATAL accident General Mass of Earth

41 Electrical Hazards Electric shock electrocution Caused by simultaneous contact of two parts of the body with either: Phase (live) and Neutral (Single Phase System) Phase and another Phase (3 phase System) Phase (live) and Earth.

42 Effects of Electric Shock Involuntary muscular contraction Respiratory paralysis (Asphyxia) Surface and deep tissue burns Lack of Oxygen in blood, Loss of consciousness Ventricular fibrillation of heart (spasms) Death in 3-7 minutes if no intervention (CPR).

43 Effects of Electric Shock depend on: Level of Voltage Duration of shock Body Resistance Insulating material (e.g. shoes, gloves) Path of current Person s health (e.g. heart condition) Age.

44 Effects of Electric Shock on Nervous System Threshold of perception Mild shock Threshold of let-go Very severe shock Fatal ma 2-10 ma ma ma > 50 ma 230 volts will result in a current of approx ma through the body Fuses & MCBs do not protect against electrocution.

45 Electrical Burns Flash - radiant heat Spatter with molten copper Burns at entry and exit points of current from body.

46 Protection Against Electric Shock Proper Earthing and Bonding Use of Earth Leakage Circuit Breaker (RCD) Safe System of Work (Lockout/Tagout) Use of Insulated Gloves, Use of Insulated Footwear or Insulated Mat Use of Double Insulated Work Equipment Regular Inspection & Testing of Installation and Equipment

47 Electrical Device Safety 1. Properly fitted plug tops 2. Plug tops should have the correct fuse 3. Routine Safety Testing 4. Do not place fluids on top of electrical devices 5. Do not plug in equipment when you have wet hands 6. Report all faults 7. Report all frayed cables, broken plugs or any plugs that feel warm.

48 The Electrical Circuit Another Fault that can occur is what s called a Short Circuit. This is a very low resistance connection between the phase/live and neutral in a single phase system or between phases in a 3-phase system. Live Electricity Supply Neutral Fuse/mcb L O A D Main Earth The high level of current flowing as a result of the fault operates the protective device General Mass of Earth Earth Rod

49 Electrical Hazards Short Circuit Explosive effect of discharge. Fire. Pressure Wave Shrapnel Sound

50 Protection Against Short Circuit Use of Proper Circuit Protection. Use of Insulated Tools Adequate information about the risks Use of Full Face Visor & Helmet, Use of appropriate Arc Resistive Overalls Use of suitable barriers & screens Accompaniment by second person Effective control of work area

51 Electrical Faults If an iron, washing machine, etc., causes a fuse to blow or MCB to trip... Always isolate the appliance before restoring the power supply Always identify the fault before reconnecting the appliance The Same applies to all electrical equipment.