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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
• 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
• 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
• 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