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Basic Electrical Safety Faculty of Science

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Title: Basic Electrical Safety Faculty of Science


1
Basic Electrical Safety Faculty of Science
Health
  • Safe Lab Module
  • January 2008

2
Electrical Safety at DCU
  • Electrical Safety Awareness
  • Electricity basics few simple pointers
  • Specific laboratory examples,
  • A few Dos Donts Watch out fors

3
Content
  • I Basic Electrical Theory Ladybird
    version, no maths !
  • Voltage current
  • Electricity in the body effects on the body
  • Electricity associated hazards
  • II Electrical Appliances
  • Safety features, cables, connections, design
  • General Electrical Guidelines Precautions
  • Electrocution
  • III Specific Hazards Personal Safety

4
I Electricity
5
Basic Electrical Theory
  • Voltage driving force causes current e - to
    flow
  • AC / DC - from safety perspective - negligible
    difference
  • Single Phase / Three Phase. 3? get a
    professional
  • Circuit / loop is necessary for current to flow
  • a start point - a route - an end point

6
Voltage, Current and Resistance
  • Voltage increases gt Current increases
  • Resistance decreases gt Current increases
  • Voltage Current / Resistance - Ohms Law

7
The complete circuit
  • A complete Circuit or loop is
  • necessary for current to flow

8
A complete circuit
  • complete Circuit or loop
  • is necessary for current to flow

Current takes the path of least resistance
9
Basic Electrical Theory
  • Voltage causes a Current to flow
  • Water analogy
  • A complete Circuit is necessary for current to
    flow
  • Bird on HT wires

10
Voltages
  • Low Tension 0 gt 50V
  • Batteries AA, AAA, MP3 player
  • Car, trucks, busses 12 / 24 / 48
  • Garden lights, domestic halogen lights
  • High Tension 100 gt 300V
  • EU Mains, Electrophoresis, DART, Capacitors SM
    PSUs
  • Very High Tension 1KV
  • ESB pylons, TV tubes, photocopiers, X-Ray
    machines, Mass Spectrometers

11
Electricity in the body
12
Electricity in the body
  • Muscles
  • Muscles control all the body movements
  • Including importantly those that keep us alive
    - Breathing and Heart
  • The brain controls voluntary muscles using
    Current pulses along nerves

13
Electricity in the body
  • External current through the body causes
  • Loss of muscle control
  • Spasms Involuntary movement
  • Inability to let go
  • Burns - external internal

14
Electricity associated hazards
15
Electricity - associated Hazards
  • Indirect Injury
  • Falls from ladder
  • Thrown back. Fall to ground, onto sharp edge
  • Drop objects
  • Thermal burns Very hot equipment surface,
    explosion
  • Wires cables - Trailing leads gt trips
    damage,
  • Re-route, tidy up, cover over
  • Life Support muscles
  • Diaphragm and breathing
  • Heart Fibrillation Random, uncoordinated
    heart contractions
  • De-fribrillation High voltages (3000 V
    at 20 A) fraction of a second
  • Burns - death of tissue
  • Internal organs
  • External skin

16
END I Electrical Theory Section
17
II Electrical Appliances Safety -
design guidelines Connectors, cables
fuses Selection, maintenance use Dealing with
electrocution
18
Electrical Appliances
  • Safety guiding principle
  • keep currents and voltages inside apparatus and
    away from our bodies
  • Inherently safe - Low voltage / low current
  • Enclosures
  • Insulation
  • Safe secure connections

19
Electrical cables plugs
  • Mains cable
  • Brown Live - power
  • Blue Neutral
  • Green/yellow Earth

20
Electrical cables plugs
  • Mains cable
  • Brown Live power
  • Blue Neutral
  • Green/yellow Earth

L
N
21
Live, Neutral, Earth Fuses
22
Live, Neutral, Earth Fuses
L
N
23
  • RCD Residual Current Device
  • RCCB Residual Current Circuit Breaker
  • ELCB Electric Leakage Circuit Breaker
  • MCB Magnetic Circuit Breakers
  • RCBO Residual Current Breaker
  • with Overcurrent protection
  • current difference of gt30 mA
  • for a duration of gt30 ms

L
L
N
N
E
24
Live, Neutral, Earth Fuses
  • The Live and Neutral wires carry current around
    the circuit
  • The Earth wire is there to protect you.
  • The Earth wire can act like a back-up Neutral
    wire,
  • Many appliances have metal cases e.g. kettles,
    toasters, dishwashers, washing machines etc.
  • The Fuse is very thin piece of wire.
  • The wire has a quite low melting point. As
    current flows through the wire it heats up.
  • If too large a current flows it melts, thus
    breaking the circuit
  • Use appropriate fuse size/rating
  • Additional safety devices - RCDs, ELCBs, MCBs

25
Electrical Equipment Guidelines
26
Guidelines
  • Use low safe voltages
  • EU 230 VAC / US 110 VAC Hz
  • Select equipment appropriate for environment
    use
  • Use equipment as per manufacturers instruction
    design
  • Ensure adequate maintenance
  • Insulate and enclose live parts
  • Prevent conducting parts from becoming live.
    Earth, double insulation separate supply from
    earth, limit electric power
  • Avoid electricity where its use could be
    dangerous. Rubbing, Induction Capacitance
    effects can build up static electricity
  • Toxic - Berilium heat sinking, Incomplete
    burning can produce carbon monoxide

27
END II Electrical Appliances
28
III Electrical Hazards Personal Safety
29
Electrocution
30
Electrocution
  • Prevention Training Where are red mushroom
    switches ?
  • Response Immediately cut power, red buttons /
    switch / plug
  • If in any doubt - Do not touch victim.
  • One hand behind back, stand on insulation, tip
    with back of hand
  • Use insulating rod / stick to move wires from
    victim.
  • Call for assistance
  • Talk reassure victim
  • If unconscious then use first aid, CPR

31
Electrical Hazards Personal Safety
  • Where
  • Office home 95
  • Laboratory 5
  • Trailing wires, faulty wires
  • Mains
  • Avoid direct working with mains. Use only low
    voltages (tension )
  • Check all leads for Fraying, Proper clamping,
    Proper earthing.
  • Repairing
  • Do not repair, competency required
  • One hand behind back, tip cautiously with back of
    hand
  • Trust nobody, remove fuse, use phase tester
  • Note Switch Mode PSU, laptop chargers, CF lamps

32
Specific Hazards Personal Safety
  • Medical / sports equipment
  • Very strict regulations on equipment operation,
    design, repair
  • Never modify or tamper with such equipment
  • ECG measurements. even a few micro amps in a
    susceptible location can have massive
    consequences Basis of Heart pacemaker
  • Pace makers
  • Susceptible to strong magnetic fields NMR! ,
  • Possibly RF Micro waves
  • Solvent
  • Flammable environments require specialised
    electrical equipment
  • E.g. Fridge storage of samples stored in
    solvents
  • Cold rooms / water cooling
  • Equipment moved from a cold room with get
    condensation on its internal electrical
  • circuits Avoid this movement, Use LT, give lots
    of time to acclimatise

33
Specific Hazards Personal Safety
  • RF µW
  • Capacitive coupling, no need to touch,
  • Both can burn severely internally and externally
    depending on how focused. Think of them like an
    open air µ-wave oven
  • HT
  • Static, OK Very low current, moderate power
  • Will jump considerable distances, beware of
    capacitors
  • Power
  • Heating effect in body gt internal burns /
    damage
  • Contact burns, deep burns necrosis
  • Trailing power and signal wires - Protect
    Tidy them up

34
Specific Hazards Personal Safety
  • Other Laboratory Situations
  • Other Office Situations
  • Other Home Situations

35
Where to get more Information
  • Your Supervisor, Manager, Head of Department
  • Department Safety Statements
  • Department Safety Committees Safety Officer
  • DCU safety - WEB
  • Edinburgh HS - WEB
  • University London HS - WEB

36
Summary
  • Awareness of the need for electrical safety
  • Introduction to the source of electrical dangers
  • Your responsibility to take care
  • of yourself and others

37
  • END

38
Whats the problem?
39
M.C.Q.s
  • Q1) Use you knowledge of insulators and
    conductors to explain
  • Why the wires are made of copper
  • Why the sheaths are made of plastic.
  • Q2) Why are the pins made of brass and why is the
    case plastic?
  • Q3) Why is only the part nearest the cases
    sheathed? Why not the whole pin?
  • Q4) A table lamp usually carries a current of
    0.5A. What fuse should be put in the plug 3A,
    5A, or 13A?
  • Q5) An iron usually carries a current of 5.2A.
    What fuse should be put in the plug 3A, 5A, or
    13A?
  • Q6) A kettle is protected by an earth wire and a
    13A fuse. The live wire comes loose and touches
    the side of the kettle. The fuse blows. Explain
    why.
  • Q7) Explain why the fuse is always located on the
    live wire and not the neutral wire?
  • Q8) Describe and Explain what happens in the
    following scenarios
  • a) The earth and live wire switch
    terminals on the plug
  • b) The Live and neutral wire switch
    terminals on the plug
  • c) The neutral and earth wire switch
    terminals on the plug
  • d) When the earth wire is removed
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