Transcript Electrical Safety

Basic
Electrical Safety
Faculty of Science & Health
Safe-Lab Module
Alan Hughes
January 2017
Ver.1.0
Why this Module!
Encouraging Electrical Safety
In an Educational & Active Research Environment
Specifically
 Avoid Injury, Death – You & Others
 Avoid Equipment Damage & Loss of Research
 Awareness of your moral & legal responsibility
to yourself, colleagues & to all others
By increasing your

awareness of potential dangers & how to avoid
creating them

awareness of your skills & Limitations

providing sources of advice & information
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Overview of Module!
Encouraging Electrical Safety
in an Educational and Research Environment

Information sources

Overview of Electrical Basics

Electrical Equipment

Specific laboratory examples
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Where to get more information

Your Supervisor, Manager, Head of Department

Department Safety Statements
Department Safety Committees & Safety Officer
DCU safety - WEB



Edinburgh University H&S - WEB
University London
H&S – WEB
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These PP slides on Faculty Safety web site

Safety in Schools

Department of education document
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TODAY
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Content
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[ I ] Basic Electrical Theory
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[ Ladybird version, no maths
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Voltage & Current
Electricity in the body & effects on the body
Electricity & associated hazards
[ II ] Electrical Equipment
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Electrocution
General Electrical Guidelines & Precautions
Safety features: fuses, ELCBs, cables, connections, equipment design
[ III ] Specific Hazards & Personal Safety
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A few Do’s , Don’ts & Watch-out-for’s
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[I]
Electricity
Basic Electrical Theory
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Basic Electrical Theory
Electricity

is the flow of electrons around a circuit
Voltage [a driving force] causes Current [e - ] to flow

AC / DC -
- Negligible difference wrt Safety
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Single Phase / Three Phase.
- if 3 phase get a professional

SI units
Volts , Amps / milli-Amps and for power Watts, energy kWHrs

Circuit

necessary for current to flow
a start point - a route - an end point
Cannot keep pouring water into a sealed bottle
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Voltage, Current and Resistance
Water analogy
Water flow
Water pressure
Conductor
Pump
: electrical current flow
: voltage
: pipe
: battery
High resistance : Narrow, long pipe
Low resistance : Wide short pipe
Switch
: Slam shut, on/off valve


Voltage increases
=>
Current increases
Resistance decreases => Current increases
Voltage = Current / Resistance -
Ohms Law
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Voltages

Low Voltage

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0 => 50V
Batteries: AA, AAA, PP3, MP3 player, Android/i-Phone
Car, trucks, busses 12 / 24 / 48
Phone or laptop charger, Christmas tree LEDs, Garden lights
High Voltage [high tension, HT ] 100 => 300V


AC = = DC
EU Mains, Electrophoresis, DART power lines, Capacitors SM-PSUs
Very High Voltage [ EHT ]
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1KV +
ESB pylons, TV tubes, photocopiers, X-Ray machines, Mass Spectrometers
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The complete circuit
A complete Circuit or loop is
necessary for current to flow
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A complete circuit
.
- Complete Circuit or loop
is necessary for current to flow
- Current
takes the path of least
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Summary - basic Electrical Theory
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Voltage causes
a Current to flow
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Big voltage => Big current
Water analogy
A Complete Circuit
is necessary for
current to flow
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Bird on H.T. wires 
Power
Voltage X Current
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Electricity
&
Human Body
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‘Normal’ Electricity in the body
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Muscles
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Muscles control all body movements, activated
using small electrical currents
Including & very importantly, those that keep us
alive: our Breathing and our Heart beat

The brain controls voluntary muscles using
small current pulses along nerves

Some local autonomous circuits for involuntary
muscles e.g. Heart
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‘External’ Electricity in the body

External Current through the body overrides
all biological control and causes:

Loss of muscle control, respiratory, paralysis
including ‘Inability to let go’
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Spasms & Involuntary movement
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Fibrillation of the Heart [no heart pumping]
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Burns - external & internal
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Just a little current can kill
It is the
Current
driven through
the body
by Voltage
that creates
danger
•
Keep voltages low
•
Do not make your
body part of a circuit
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Just a Little Current Can Kill
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• 1 mA,
slight tingle is felt.
• 5 mA,
slight shock is felt, not painful but disturbing. The
average individual can let go, involuntary reactions can lead to injuries.
• 6-25 mA,
painful shock, muscular control is lost
• 9 – 30 mA,
called the freezing current or “let-go” range. many
humans cannot get their muscles to work, and they can’t open their hand
to let go of a live conductor.
• 50-150 mA,
there will be extreme pain, respiratory arrest, and
severe muscular contractions. Individual cannot let go, death is possible.
• 1000-4300 mA,
there is ventricular fibrillation. Muscular contraction
and nerve damage occur. Death is most likely.
• 10,000+ mA,
Cardiac arrest, severe burns and probable death.
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Electricity
&
Associated Hazards
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Electricity - associated hazards

Life support muscles
 Diaphragm and breathing
 Heart Fibrillation
Random, uncoordinated heart contractions
De-fibrillation:
High voltages (3000 V at 20 A) fraction of a second

Burns - death of tissue
 Internal
[organs]
 External
[skin] Usually at Exit & Entry areas
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Indirect Injury
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Falls from ladder
Thrown back. Fall to ground, onto sharp edge
Drop objects, injure an innocent bystander
Thermal burns – Very hot equipment surface, explosion
Wires & cables
Indirectly probably the most common “electrical” injury
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Electricity - associated Hazards
Wires & cables
Trailing leads
Trips, falls & injury
Equipment damage
Re-route, tidy up, cover over
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Exit & entry Burns
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END
[I]
Electrical Theory Section
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Electrical Appliances
Safety guiding principles

keep currents and voltages to a minimum

inside apparatus and away from our bodies
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when a fault is detected Trip out
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Electrical Appliances
Minimise voltages [ and thus minimise current ]
 Inherently safe - Low voltage / low current
Keep Voltages away from our bodies
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Enclosures
Insulation
Connections safe & secure
Trip out when fault detected
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Safety features – Fuses, ELCBs, Switches
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Electrical cables & plugs
Mains cable
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Brown
Blue
Green/yellow
Live - power
Neutral
Earth
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Electrical plugs, cables & fuses
Mains cable

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
Brown
Live power
Blue
Neutral
Green/yellow Earth
L
N
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Electrical fuses & ELCBs
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Live, Neutral, Earth & Fuses
L
N
L
N
E
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Live, Neutral, Earth & Fuses
L
N
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ELCB
RCD
Electric Leakage Circuit Breaker
Residual Current Device
RCCB
MCB
RCBO
Residual Current Circuit Breaker
Magnetic Circuit Breakers
Residual Current Breaker
with Over-current protection


current difference of
for a duration of
L
> 30 mA
~ 30 ms
L
N
N
E
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Fuse Vs ELCB
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A Fuse breaks the circuit
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When too much current attempts to flow through an appliance
Usually the excess current is in Amps [Very dangerous] and it
happens in less than a second
Must be replaced
An
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ELCB breaks the circuit
When there is a difference between the current flowing in the Live
and in the Neutral wires
Usually operates when the difference is ~ 30mA [borderline safe]
Operates very fast, in a small fraction of a second
Is resettable
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Electrical extension boards
Emergency Stop Switch
•
•
•
Avoid where possible
Do not daisy-chain
Check total current
•
•
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Know where they are
Check occasionally
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Electrical summary
Live and Neutral wires carry current to equipment

The
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The Earth wire is there to protect you.
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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.
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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
ELCBs, RCDs Important Safety Devices

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Leakage-to-earth sensors with trip out
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Electricity Safety Summary

High Voltage causes High current


Electricity require a circuit

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Ensure that all equipment has an earth connection
When a fault occurs
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Ensure your body does nor complete the circuit
Electric current takes the easiest path


Keep voltages low
All equipment should have fuses and ELCBs
Wires & cables
Probably the single most common electrical hazard
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Equipment & Laboratory Guidelines
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Use low & safe voltages: Mains voltages are dangerous 230 VAC
Select equipment appropriate for environment & use
Avoid electricity where its use could be dangerous.
Use equipment as per manufacturer’s instruction & design
Ensure adequate maintenance, damaged case, frayed leads
Insulate and enclose live parts
Ground casings to earth
Prevent conducting parts from becoming live. Earth, double
insulation, separate supply from earth, limit electric power
Rubbing, Induction & Capacitance effects can build up static
electricity
Avoid use of daisy-chained power extension boards
Toxic - Beryllium heat sinks, Incomplete burning can produce
carbon monoxide & other toxicfumes
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Electrical Hazards & Safety
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Safety in Schools
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Good Housekeeping
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Water & electricity do not go well together
Water makes you a better conductor allowing MORE current to flow
Mains
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Well organised & laid out laboratories
Adequate Class control
Water
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1.3
3.1
Department of education document
Electrical Services & equipment
Pages 10 & 11
General Electrical safety precautions
Pages 20 & 21
Avoid direct working with mains. Use low voltages
Check all leads for: Fraying, Proper clamping, Proper earthing.
Repairing
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Do not repair, competency required
Trust nobody, remove fuse, use phase tester
One hand behind back, tip cautiously with back of hand
Note: Switch Mode PSU, laptop chargers, CF lamps [high voltages persists on capacitors long after switch off]
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Environmental issues
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Don’t waste power -Turn off
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Use Low power versions of equipment
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15c per kWh
Flat screen Vs old CRT tube TV
Lighting: LED, fluorescent, CFL, Filament
Reduce and recycle, waste considerations!
Avoid hazardous materials
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Mercury fluorescent tubes & CFLs
Cadmium & lead from re-chargeable batteries
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Electrical Hazards & Personal Safety
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Used where!
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Office & home
Laboratory

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Trailing wires, faulty wires
Mains

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
95%
5%
Avoid direct working with mains. Use low voltages
Check all leads for: Fraying, Proper clamping, Proper earthing.
Repairing

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
Do not repair, competency required
Trust nobody, remove fuse, use phase tester
One hand behind back, tip cautiously with back of hand
Note: Switch Mode PSU, laptop chargers, CF lamps [high voltages persists on capacitors long after switch off]
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Some examples of electrical hazards

Electronics experiments

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Use acceptable low voltage
Mains operated LT power supplies
Wrong connection – IC / electrical component over heats, shatters

Van De Graaff generator
High voltage
Low current !

Teltron tubes
High voltage
Vacuum implosion

Magnetic experiments
High currents
Heart pace makers
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Hot plates
Burns
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Electrophoresis
High voltages
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Trailing Power and Signal wires - Protect & Tidy them up
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Sometimes forgotten hazards
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Medical / Sports equipment
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Pace makers
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Susceptible to strong magnetic fields [NMR! ],
Possibly RF & Micro waves interference
Chemical Solvents


Very strict regulations on equipment operation, design, repair
Never modify or tamper with such equipment
ECG measurements. even a few micro amps direct to the heart can have
massive consequences [basis of a heart pacemaker ]
Flammable environments require specialised electrical equipment
E.g. Spark-free fridge for storage of samples dissolved in solvents
Cold rooms / water cooling

Equipment moved from cold room can get condensation on its internal
electrical circuits. Avoid this movement, Use L.T. and give lots of time to
acclimatise
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Yet more examples

RF & µW
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EHT
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Static, OK [Very low current, moderate power] nearby Solvents!
Will jump considerable distances,

Beware of capacitors


Power



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
Heating effect in body
=> internal burns / damage
Contact burns, deep burns & necrosis
Trailing Power and Signal wires - Protect & Tidy them up
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Specific Hazards & Personal Safety

Other Laboratory Situations ?

Other Office Situations ?

Other Home Situations ?
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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.

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Call for assistance
Talk & reassure victim
If unconscious then use first aid, CPR
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END
[ II ]
Theory Section
Electrical Appliances
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SUMMARY
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Summary

Awareness of the need for electrical safety

Potential Source of electrical dangers

Your responsibility to take care of
Yourself and Others

Note Safety References for future use

If unsure never be afraid to ask
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Where to get more information

Your Supervisor, Manager, Head of Department

Department Safety Statements
Department Safety Committees & Safety Officer
DCU safety - WEB



Edinburgh University H&S - WEB
University London
H&S – WEB

http://sce.e-smartonline.net/elec_safety-smart/index.html

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END
Thanks for your attention
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