LIN155 Electrical Hazards & Lab Safety PDF

Electrical Hazards & Lab Safety LIN155 – Electronic Lab & Instrumentation Techniques School of Electronics and Mechanical Engineering Technology (SEMET) Textbook References: Chapter 13, p. 253-262 Agenda Lab Safety General Electrical Safety Electric Cords SEMET Lab Safety Rules/Pol...

Electrical Hazards & Lab Safety LIN155 – Electronic Lab & Instrumentation Techniques School of Electronics and Mechanical Engineering Technology (SEMET) Textbook References: Chapter 13, p. 253-262 Agenda Lab Safety General Electrical Safety Electric Cords SEMET Lab Safety Rules/Policy Electrical Shock Electrical Hazards Grounding Overcurrent Protection Devices Insulation failures Detecting/Reducing Electrical Hazards Canadian Electrical Standards 2  Safety Note Electricity is dangerous. Whenever you use electrical appliances and equipment, whether at home or at work, there is always a risk of an accident, especially of electric shock. Image source: http://www.freeimageslive.com/galleries/workplace/energy/pics/electric_danger.jpg 3 Lab Safety When working in the electrical laboratory, observe proper safety precautions. There are potential hazards in the electrical labs, and failure to follow the procedures can cause accidents. The most common hazard in an electrical lab is electric shock. (For LIN155 labs: also a high risk of burns) 4 General Safety Rules (1) Never work alone. Use instruments and power tools provided with three-wire power tools or double insulated power tools approved by CSA (Canadian Standard Association - www.csa.ca). Always shut off power before handling wiring. Check all power cords for signs of damage. Always wear shoes. 5 General Safety Rules (2) Never handle electrical instruments when your skin is wet. Hot soldering irons should not be left unwatched. Never wear loose clothing around machinery. Make sure that there is adequate illumination for the task area. Assume that all capacitors are charged. 6 General Safety Rules (3) Periodically inspect insulation. Verify circuit voltages before doing work. Do not use water to put out an electrical fire. Use fuses and circuit breakers for protection against excessive current. 7 Electric Cords There are 2500 annual workplace injuries linked to improper use of electric cords. Never use an extension cord for an extended period of time. Never cover extension cords with rugs or mats in an attempt to prevent tripping – hide shorts and bare spots. Never just unplug an extension cord that feels hot in order to cool it down. Image source: https://www.statefarm.com/simple-insights/residence/extension-cord-safety-what-to-do-and-what-to-avoid 8 SEMET Lab Safety Rules Students are expected to conduct themselves in a professional and safe manner at all times. While in a SEMET lab, be aware of the nearest fire extinguisher and location of the safety station with its supplies. Food or drink is not allowed in SEMET labs at any time. Safety glasses and other necessary precautionary or safety equipment will be used or worn. No open-toed shoes or sandals. Long hair should be tied back. Electrostatic wristbands are required in the labs with ESD sensitive electronics (for example: FPGAs and microcontrollers). 9 SEMET Lab Safety Rules continued All laboratory equipment brought into SEMET labs must be CSA approved and in good working order. This will require you to inspect your equipment on a consistent basis. Vandalism of any kind will not be tolerated. Students should note that security cameras are in place for the protection of college property and occupant safety. Offenders will be subject to the terms of the College’s Student Rights and Responsibilities Policy. Failure to comply with the SEMET Laboratory Code of Behaviour will result in a lab grade of zero (0). 10 SEMET Lab Safety Policy Safety glasses are mandatory in the following electrical labs when the power in ON: K2200, A4056, A4058, A4060, A4066, A4068, A4070, A4071, A4072, A4073 Each lab has a safety station, telephone, and an issue sheet. Student Awareness. No food or drink in the SEMET labs at any time. 11  Safety Station Image source: Seneca faculty, SEMET Labs 12  Power Buttons ON OFF Image source: Seneca faculty, SEMET Labs 13  What is Electric Shock? Electric Shock – The effect caused when electric current passes through the human body. The severity of an electric shock varies with the age, gender, and physical condition of the victim. The threshold of perception of current for most humans is 1 mA. The sensation that many people feel at this threshold level is an unpleasant tingling or heating at the point of contact. 14 Effect of Current on the Human Body Current Intensity Effect (1 second contact) 1 mA Threshold of perception. Tingling or heat. 5 mA Not painful but disturbing. Accepted as the maximum harmless current intensity. 6 mA – 16 mA Painful shock. Referred to as the “let-go” or freezing current range. Start to lose muscular control. 17 mA – 99 mA Extreme pain. Difficulty breathing. Cannot “let-go” due to severe muscular contractions. Death possible. 100 mA – 2000 mA Ventricular fibrillation (uneven, uncoordinated pumping of the heart). Nerve damage. Death likely. > 2000 mA Cardiac arrest, severe burns. Death probable. 15  Low Voltage can also Kill The severity of the injury can increase the longer the victim is exposed to the shock current. Low voltages can be extremely dangerous because the degree of injury depends not only on the amount of current but also on the length of time the body is in contact with the circuit. Some victims have stopped breathing when shocked with currents from voltages as low as 49 volts. For example, a shock current of 100 mA applied for 3 seconds can cause injuries as severe as a current of 900 mA applied for a fraction of a second. 16  High Voltage Lead to Serious Injuries A current flow is directly proportional to the voltage supplying the current. That is why the higher the voltage, the higher the shock current flowing through the victim’s body. Therefore, the injuries will be more severe. At high voltage (eg. 600 volts), the shock current can be as high as 4 amps. Trauma due to high current shocks: damage to the heart and other internal organs, clotting in internal blood vessels, nerve damage in the area where the skin touches the electrified object, severe tissue burns, severed limbs. 17  First Aid for Electric Shock 1) The first step in helping a victim of electric shock is to shut off the power. 2) If this attempt fails, try to break the contact of the victim with the power source without injuring yourself. Do not touch the victim with your bare hands. 3) Call 911. 18  Sources of Electrical Hazards Contact with a bare wire carrying current Working with equipment that lacks the UL, CSA, or Special Inspection label Electrical Equipment that has not been properly grounded Working with electrical equipment on damp floors Using metal ladders to work on electrical equipment Working on electrical equipment without ensuring that the power has been shut off Lighting strikes 19  Incidences of Electrocution Electrocution accounts for about 20% of all fatalities in the Canadian construction industry. In Ontario in the 10 years from 2006 to 2015*,  There were 94 deaths due to electrical fires.  There were 63 deaths due to electrocution: About 60% of those occurred in public places. More than 60% were occupational electrical-related. Of the occupations, 25% were electrical tradespeople. Electrocutions and electric shock lost time injury claims outnumbered electrical burn injuries by 1.5 times. Each year, about 110 kids in Ontario suffer electrical injuries. 20  Ground The concept of ground and grounding are vital and integral concepts used in the design of electrical measurement systems. Measurements of potential difference are relative: the voltage level of any point in a circuit must always be compared to some reference level. The reference level is assigned a voltage of “zero” (0 volts) and is known as the circuit ground. 21 Ground continued Different kinds of grounds: Earth ground, floating chassis ground, digital ground. (Each has its own schematic symbol.) AC electrical systems: Ground is a separate conductor that provides a low- impedance path directly to earth ground. It does not carry any current. If a hazardous voltage spike occurs on the line, it will protect the equipment and users. DC electrical systems: Ground is usually the negative side of the source (eg. battery). This means all current in the circuit will return to the source through the common ground rail. 22  Common 3-wire Wall Plug Wire 1 (black - Live) is connected to the terminal of higher potential of the AC source. It will carry a current to the load. Wire 2 and Wire 3 are both connected to Ground. Wire 2 (white - Neutral) is connected to ground at the service panel and also carries the return current from the load back to the source. Wire 3 (green - Ground) is a non-current carrying wire under normal operating conditions. Its purpose is to supply a low resistance path directly back to the service panel, in case there is a rogue voltage on the line. 23 Wiring Diagram of a 3-wire Wall Plug Image modified from: https://learnelectronicshelp.blogspot.com/2015/12/3-pin-plug-wiring-diagram.html 24 Grounding Ultimately, the most important reason for grounding electrical equipment is to provide protection against electrical shock. Electrical instruments and household appliances are built so that their enclosures are electrically isolated from the wires that carry power to their circuits. This prevents the equipment cases from accidentally becoming live (or “hot”), which can cause a shock to operators or surrounding items. Especially in high voltage operations, the equipment shall be grounded and the operator shall not be grounded. 25 Overcurrent Protection Devices Fuses Circuit Breakers Image Source: https://instrumentationtools.com/advantages-disadvantages-fuse-electrical-circuit/ Image source: https://www.electricaltechnology.org/2021/05/types-of-circuit-breakers.html 26  Insulation Failure Direct Sunlight Sparks or arcs from discharging static electricity – holes in insulation Repeated exposure to elevated temperatures Animals… rodents, insects chewing on insulation Contact with abrasive surfaces Moisture and humidity Image source: https://strikecheck.com/2018/07/05/water-damage-electrically-powered-items/ Image source: https://beatpests.com/how-can-rats-chew-through-metal 27  Detection of Electrical Hazards Circuit tester – Test equipment with two wire leads capped by probes and connected to small bulb. 110-220 V – On/Off Receptacle wiring tester is a device with two standard plug probes for insertion in an ordinary 110 V outlet. Continuity tester can be used to determine whether a conductor is properly grounded or has a break in a circuit. Image source: https://images-na.ssl-images-amazon.com/images/I/41BLp8PjZzL.jpg Image source: https://images-na.ssl-images-amazon.com/images/I/81jikGfI7IL._SY450_.jpg Image source: https://www.amazon.ca/Fluke-1AC-A1-II-Volt-Alert-Non-Contact-Voltage/dp/B000EJ332O 28  Reducing Electrical Hazards Grounding provides a safe path for hazardous voltages. Ground Fault Circuit Interrupter – GFCI – can detect the flow of current to the ground and open the circuit, thereby interrupting the flow of current. Fuses consist of a metal strip or wire that melts if a current above a specific value is conducted through the metal. Image source: Seneca faculty, in a SEMET electrical lab 29  Reducing Electrical Hazards continued Double insulation on tools have a plastic non-conductive housing in addition to standard insulation. Interlocks disable a circuit if a second mechanism disables, eg. an interlock key is missing or a barrier is breached. Image source: https://electricianlab.com/best-insulated-screwdrivers-electricians/ Image source: http://www.ideadigitalcontent.com/files/11003/09008926807a544b.jpg 30  Canadian Electrical Standards Rules and regulations regarding installation, wiring and maintenance of electrical equipment are covered by the Canadian Electrical Code. Image source: https://www.csagroup.org/store/product/CSA_C22.1%3A24/ 31 Questions 32 Works Cited David Goetsch, “Occupational Health and Safety for Technologist, Engineers, and Managers”, Canadian Edition, Pearson Canada, March 2, 2018 Stanley Wolf, “Student Reference Manual for Electronic Instrumentation Laboratories”, Pearson/Prentice Hall, 2004 33