Electrical/Electronic Safety Scratching The Surface

Transcription

1 Electrical/Electronic Safety Scratching The Surface Copyright 2004 D. L. Gould & Niagara College Niagara College - Technology

2 Safety - A Part Of The Job! Be safety conscious. There s a difference between electrical shock and electrocution. Avoid the danger. Personal protection for your senses. Safety in design.

3 Be Safety Conscious Note the location of emergency and first aid stations Obey all posted warning signs. Report dangerous conditions to the supervisor Caution others in violation of safety rules. Lockout all electrical circuits when working on them. Avoid horseplay(distractions) and practical jokes.

4 Threshold of Sensation To Death 10 uamps - the threshold of sensation 1 mamps - a shock that can be felt as a mild tingling sensation.(5 mamps - GFI trip rate) 10 mamps - a shock that can cause muscular paralysis. 50 mamps - a shock that can cause severe breathing difficulties and muscular paralysis(can t let go phenomenon) - may be fatal 100 mamps - produces a shock that can cause death (electrocution) if it lasts for a second or more.

5 Electrical Shock Voltage - The force that causes current to flow through a circuit. Current - Dependent on the circuit s resistance and the value of the voltage Resistance - opposition to the flow of current. Body resistance = 10K to 50K depending on how good a contact you make with the live circuit. (wet skin, cuts, abrasions decrease body resistance)

6 Avoiding The Danger Don t work on live circuits except when absolutely necessary. One hand in your pocket to measure high voltage. Dangerous voltages can be held in some devices after the power is removed. (CRTs, caps) Hand tools used must be electrically insulated. Look for the hazards. (power cords, fuses, worn tools) Use an isolation transformer when servicing.

7 Read the MSDS for the chemicals you use. Make sure you familiar with the operation of a power tool before you use it. Arrange tools so that line cords (soldering iron) and sharp edges are not hanging over the edge of the bench. Never shake molten solder from a soldering iron - use a damp sponge. All decanted chemicals must be clearly labeled. Never take food or drink into the work area. Hold the cord cap to remove a line cord from an outlet, don t pull on the line cord.

8 Safety And The Senses Your Eyes Injury can cause permanent blindness. Clipping component leads - Safety Glasses Solder splash - Safety Glasses A splash or spray of chemicals - Safety Glasses, chemical proof goggles or a face shield A flash of intensely bright light - Filtered Safety Glasses. Lasers - Laser Safety Glasses Compressed air - Safety Glasses Power driven machinery and exposed electrical circuits. - Safety Glasses

9 Safety And The Senses Your Ears Loud sounds & high-pitched tones can cause permanent hearing loss. Power tools - ear plugs or ear muffs Industrial noise (drop forge, sheet metal cutter, metal stamping machine) - ear plugs or ear muffs Aeronautics industry (airports) - ear plugs or ear muffs

10 Safety And The Senses Your Nose Toxic fumes can cause damage to the membranes lining the nasal passages. Your nose is a pathway to your lungs. Printed circuit board chemicals - drawn from the area by vent hoods and exhaust fans. Microelectronics process chemicals - drawn from the area by vent hoods and exhaust fans. Contact cleaners, flux removers, etc. - used in well ventilated areas.

11 Safety And The Senses Your Mouth You could be unknowingly ingesting foreign and hazardous particles. Printed circuit chemicals on your hands. Acid salts picked up on the hands during a chemical process Cleaning solvents & flux removers etc. on the hands. Absentmindedly using your mouth as a third hand to hold the solder. Stripping the insulation from a piece of wire with your teeth.

12 Contaminants on the hands usually end up in the mouth - nail biting - consuming food. Wash your hands after using any chemicals or working in a chemical environment. Wear gloves when working with chemicals. Use a vice as a third hand or ask for help if you need it during a soldering process.. Read the MSDS before handling any chemical.

13 Safety And The Senses Your Skin Injury can cause permanent skin damage Nerve endings may be destroyed because of an electrical shock, burns from soldering irons & solder, hot components and chemicals (acids). Acid proof gloves, an apron and a face shield may be required when working with caustic chemicals. Secure loose clothing, use a hair net, and remove all jewelry around power driven machinery and exposed electrical circuits.

14 Safety in Design The Isolation Transformer Component polarity Fuses Three wire power cords AC leakage test ESD

15 The Isolation Transformer Purpose - to isolate the load from the test equipment. Accomplished by - inducing the 120VAC into the secondary of the isolation transformer. 120 VAC Input 120 VAC Output

16 Why the Isolation Transformer? Power Plug Test Equipment 120 VAC Between Metal Cases Power Plug Load Under Test 120 VAC Source Two pieces of equipment not connected to the same AC neutral.

17 Component Polarity Electrolytic capacitors - polarized incorrectly may explode violently Tantalum capacitors - polarized incorrectly may explode violently Semiconductors - polarized incorrectly may burn up in the circuit. All these polarity problems may result in fires and flying particles.

18 Fuses A safety device placed in equipment to help protect us from the hazards of fires and explosions as a result of excessive current draw due to a circuit malfunction.

19 Three Wire Power Cords Ground 3 Wire Cord Cap Lighted Rocker Switch Panel Mount Fuse Holder Transformer

20 AC Leakage Test No greater than 0.3 Vrms should be measured between the chassis or I/O terminals with respect to hydro ground! A Vrms reading of 0.3 represents a current flow of 0.2 ma. Any reading higher than this would indicate a safety hazard.

21 ESD CMOS & Static Electricity CMOS-complementary metal-oxide semiconductor You can zap as well as be zapped. Use antistatic materials, antistatic wrist straps, conductive foam, aluminum foil - all pins of the device at the same potential. Disconnect the power to the circuit when inserting or removing MOS devices. To avoid static discharge from a soldering iron use one with a grounded tip.

22 Summary Safety as a part of the job. Commonsense safety attitudes. Threshold of sensation. Avoid the danger. Your five senses and safety. Safety in design.

23 Where to get more information Electronic Fabrication Second Edition by Gordon Shimizu Electronic Project Design and Fabrication Third Edition by Ronald A. Reis Electronic Techniques Shop Practices and Construction Fifth Edition by Robert S. Villanucci. Dangerous Voltages The Fatal Current