electrical/electronic safety - niagara...

Electrical/Electronic SafetyElectrical/Electronic SafetyScratching The SurfaceScratching The Surface

Copyright © 2004D. L. Gould & Niagara College

Niagara College - Technology

Safety Safety -- A Part Of The Job!A Part Of The Job!l Be safety conscious.l There’s a difference between electrical shock

and electrocution.l Avoid the danger.l Personal protection for your senses.l Safety in design.

Be Safety ConsciousBe Safety Conscious

l Note the location of emergency and first aid stations

l Obey all posted warning signs.l Report dangerous conditions to the supervisorl Caution others in violation of safety rules.l Lockout all electrical circuits when working on

them.l Avoid horseplay(distractions) and practical jokes.

Threshold of Sensation Threshold of Sensation To DeathTo Death

l 10 uAmps - the threshold of sensationl 1 mAmps - a shock that can be felt as a mild

tingling sensation.(5 mAmps - GFI trip rate)l 10 mAmps - a shock that can cause muscular

paralysis.l 50 mAmps - a shock that can cause severe

breathing difficulties and muscular paralysis(can’t let go phenomenon) - may be fatal

l 100 mAmps - produces a shock that can cause death (electrocution) if it lasts for a second or more.

Electrical ShockElectrical Shock

l Voltage - The force that causes current to flow through a circuit.

l Current - Dependent on the circuit’s resistance and the value of the voltage

l Resistance - opposition to the flow of current.l Body resistance = 10K to 50K depending on how

good a contact you make with the live circuit. (wet skin, cuts, abrasions decrease body resistance)

Avoiding The DangerAvoiding The Dangerl Don’t work on live circuits except when absolutely

necessary.l One hand in your pocket to measure high voltage.l Dangerous voltages can be held in some devices

after the power is removed. (CRTs, caps)l Hand tools used must be electrically insulated.l Look for the hazards. (power cords, fuses, worn

tools)l Use an isolation transformer when servicing.

l Read the MSDS for the chemicals you use.l Make sure you familiar with the operation of a

power tool before you use it.l Arrange tools so that line cords (soldering iron)

and sharp edges are not hanging over the edge of the bench.

l Never shake molten solder from a soldering iron -use a damp sponge.

l All decanted chemicals must be clearly labeled.l Never take food or drink into the work area.l Hold the cord cap to remove a line cord from an

outlet, don’t pull on the line cord.

Safety And The SensesSafety And The SensesYour EyesYour Eyes

l Injury can cause permanent blindness.l Clipping component leads - Safety Glassesl Solder splash - Safety Glassesl A splash or spray of chemicals - Safety Glasses,

chemical proof goggles or a face shieldl A flash of intensely bright light - Filtered Safety

Glasses.l Lasers - Laser Safety Glassesl Compressed air - Safety Glassesl Power driven machinery and exposed electrical

circuits. - Safety Glasses

Safety And The SensesSafety And The SensesYour EarsYour Ears

l Loud sounds & high-pitched tones can cause permanent hearing loss.

l Power tools - ear plugs or ear muffsl Industrial noise (drop forge, sheet metal cutter,

metal stamping machine) - ear plugs or ear muffsl Aeronautics industry (airports) - ear plugs or ear

muffs

Safety And The SensesSafety And The SensesYour NoseYour Nose

l Toxic fumes can cause damage to the membranes lining the nasal passages.

l Your nose is a pathway to your lungs.l Printed circuit board chemicals - drawn from the

area by vent hoods and exhaust fans.l Microelectronics process chemicals - drawn from

the area by vent hoods and exhaust fans.l Contact cleaners, flux removers, etc. - used in well

ventilated areas.

Safety And The SensesSafety And The SensesYour MouthYour Mouth

l You could be unknowingly ingesting foreign and hazardous particles.

l Printed circuit chemicals on your hands.l Acid salts picked up on the hands during a chemical

processl Cleaning solvents & flux removers etc. on the hands.l Absentmindedly using your mouth as a third hand to

hold the solder.l Stripping the insulation from a piece of wire with your

teeth.

• 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.

Safety And The SensesSafety And The SensesYour SkinYour Skin

l Injury can cause permanent skin damagel Nerve endings may be destroyed because of an

electrical shock, burns from soldering irons & solder, hot components and chemicals (acids).

l Acid proof gloves, an apron and a face shield may be required when working with caustic chemicals.

l Secure loose clothing, use a hair net, and remove all jewelry around power driven machinery and exposed electrical circuits.

Safety in DesignSafety in Design

l The Isolation Transformerl Component polarityl Fusesl Three wire power cordsl AC leakage testl ESD

The Isolation TransformerThe Isolation Transformer

l Purpose - to isolate the load from the test equipment.

l Accomplished by - inducing the 120VAC into the secondary of the isolation transformer.

120 VACOutput

120 VACInput

Why the Isolation Transformer ?Why the Isolation Transformer ?

Test Equipment

Load Under Test

120 VAC BetweenMetal Cases

Power Plug

Power Plug

120 VAC Source Two pieces of equipment not connected to the same AC neutral.

Component PolarityComponent Polarity

l Electrolytic capacitors - polarized incorrectly may explode violently

l Tantalum capacitors - polarized incorrectly may explode violently

l Semiconductors - polarized incorrectly may burn up in the circuit.

l All these polarity problems may result in fires and flying particles.

FusesFuses

l 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.

Transformer

LightedRocker Switch

Ground

3 Wire Cord Cap

PanelMountFuse Holder

Three Wire Power CordsThree Wire Power Cords

AC Leakage TestAC Leakage Test

l No greater than 0.3 Vrms should be measured between the chassis or I/O terminals with respect to hydro ground!

l A Vrms reading of 0.3 represents a current flow of 0.2 mA. Any reading higher than this would indicate a safety hazard.

ESDESDCMOS & Static ElectricityCMOS & Static Electricity

l CMOS-complementary metal-oxide semiconductor

l You can zap as well as be zapped.l Use antistatic materials, antistatic wrist straps,

conductive foam, aluminum foil - all pins of the device at the same potential.

l Disconnect the power to the circuit when inserting or removing MOS devices.

l To avoid static discharge from a soldering iron use one with a grounded tip.

SummarySummary

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

Where to get more Where to get more informationinformation

l Electronic Fabrication Second Editionby Gordon Shimizu

l Electronic Project Design and Fabrication Third Edition by Ronald A. Reis

l Electronic Techniques Shop Practices and Construction Fifth Edition by Robert S. Villanucci.

l Dangerous Voltages

l The Fatal Current