basic electrical safety - dublin city university · electrophoresis, dart power lines, capacitors...

January 2020

Ver.1.5

Basic

Electrical SafetyFaculty of Science & Health

Safe-Lab ModuleAlan Hughes

January 2020 Ver.1.5 2

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 & your limitations awareness of sources of advice & information


Overview of today!

….. Increased Safety by awareness of ….

Your Permissions your Limitations

Information sources

Education Overview of Electrical Basics

Electrical Equipment

Specific laboratory examples

-



Information sources 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

These PP slides Faculty Safety web site

‘Safety in Schools’ Department of education document


Electricity & Safety

[ I ] Basic Electrical Theory [ Ladybird version, no maths ]

Voltage & Current

Electricity in the body & effects on the body

Electricity & associated hazards

[ II ] Electrical Equipment Electrocution

General Electrical Guidelines & Precautions

Safety features: fuses, ELCBs, cables, connections, equipment design

[ III ] Specific Hazards & Personal Safety A few Do’s , Don’ts & Watch-out-for’s


-


[ I ]

ElectricityBasic Electrical Theory


Basic Electrical Theory

Voltage [a driving force] causes Current [e - ] to flow AC / DC - - Negligible difference wrt Safety

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 bottle

Electricity is the flow of electrons around a circuit


Voltage, Current and Resistance

Voltage increases => Current increases

Resistance decreases => Current increases

Voltage = Current / Resistance - Ohms Law

Water analogy

Water flow : electrical current flow

Water pressure : voltage

Conductor : pipe

Pump : battery

High resistance : Narrow, long pipe

Low resistance : Wide short pipe

Switch : Slam shut, on/off valve


Voltages AC == DC

Low Voltage 0 => 50V Batteries: AA, AAA, PP3

Car, trucks, busses 12 / 24 / 48

Phone or laptop charger, Christmas tree LEDs, Garden lights

High Voltage [high tension, HT ] 100 => 500V IE/EU Mains

Electrophoresis, DART power lines, Capacitors SM-PSUs

Very High Voltage [ EHT ] 1kV + ESB pylons, oldTV tubes, photocopiers, X-Ray machines, Mass

Spectrometers


The complete circuit

A complete Circuit or loop is

necessary for current to flow


A complete circuit

- Complete Circuit or loop

is necessary for current to flow

- Current takes the path of least resistance

.


Summary - basic Electrical Theory

Voltage causes

a Current to flow

Big voltage => Big current

Water analogy

A Complete Circuit

is necessary for

current to flow Bird on H.T. wires

Insulation to prevent a circuit

Power Voltage X Current


Electricity

&

Human Body


‘Normal’ Electricity in the body

Muscles Muscles control all body movements

They are 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

Electrical synapse

October 2016 Ver. 1.4 17

Biological

mechanical and

electrically conductive link

between two

neighbouring neurons


‘External’ Electricity in the body

External Current through the body overrides

all biological control :

Loss of muscle control, respiratory, paralysis

including ‘Inability to let go’

Spasms & Involuntary movement

Fibrillation of the Heart [no co-ordinated heart beat]

Burns - external & internal


Just a little current can kill

It is the

Currentdriven through

the body

by Voltagethat creates

danger

• Keep voltages low

• Do not make your

body part of a circuit

Just a Little Current Can Kill • 1 mA A slight tingle is felt.

• 5 mA light shock is felt, not painful but disturbing.

Average individual can let go

• 6-25 mA painful shock, muscular control is lost

involuntary reactions can lead to injuries.

• 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,

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.



Electricity

&

Associated Hazards


Electricity - associated hazards Life support muscles

Diaphragm and breathing Heart Fibrillation Random, uncoordinated heart contractions

Defibrillators High voltages (3000 V at 20 A) fraction of a second

Burns - death of tissue Internal [organs] External [skin] Usually at Entry & Exit areas

Indirect - Injury Falls from ladder Thrown back. Fall to ground, onto sharp edge Drop objects, injure an innocent bystander Thermal burns – Very hot equipment surface, explosion

Indirect - Wires & cables Indirectly probably the most common “electrical” injury


Electricity - associated Hazards

Wires & cablesTrailing leads

Trips, falls & injury

Equipment damage

Re-route, tidy up, cover over


Exit & entry Burns


END

[ I ] Electrical Theory Section


-


Electrical Appliances

Safety guiding principles

keep currents and voltages to a minimum

inside apparatus and away from our bodies

when a fault is detected, Trip out



Minimise voltages [ and thus minimise current ]

Inherently safe - Low voltage / low current

Keep Voltages away from our bodies Enclosures

Insulation

Connections safe & secure

Trip out when fault detected Safety features – Fuses, ELCBs, Switches


Electrical cables & plugs

Mains cable Brown Live - power

Blue Neutral

Green/yellow Earth


Electrical plugs, cables & fuses

Mains cable

Brown Live power

Blue Neutral

Green/yellow Earth

L

N


Electrical fuses & ELCBs


Live, Neutral, Earth & FusesL

N

L

N

E


Live, Neutral, Earth & Fuses

L

N


ELCB Electric Leakage Circuit Breaker

RCD Residual Current Device

RCCB Residual Current Circuit Breaker

MCB Magnetic Circuit Breakers

RCBO Residual Current Breaker

with Over-current protection

current difference of > 30 mA

for a duration of ~ 30 ms

L

N

E

L

N


Fuse Vs ELCB

A Fuse breaks the circuit 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 ELCB breaks the circuit

When there is a difference between the current flowing in the Liveand 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


Electrical extension boards

Emergency Stop Switch

• Avoid where possible

• Do not daisy-chain

• Check total current

• Know where they are

• Check occasionally


Electricity summary The Live and Neutral wires carry current to equipment

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

ELCBs, RCDs Important Safety Devices Leakage-to-earth sensors with trip out


Electricity Safety Summary

High Voltage causes High current Keep voltages low

Electricity require a circuit Ensure your body does nor complete the circuit

Electric current takes the easiest path Ensure that all equipment has an earth connection

When a fault occurs All equipment should have fuses and ELCBs

Wires & cables

Probably the single most common electrical hazard


END

[ II ]

Theory Section



-


Equipment & Laboratory Guidelines

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


Good General Electrical Safety

Safety in Schools Department of education document

1.3 Electrical Services & equipment Pages 10 & 11

3.1 General Electrical safety precautions Pages 20 & 21

Good Housekeeping Well organised & laid out laboratories slips, trips & falls

Adequate Class control

Water Water & electricity do not go well together

Water makes you a better conductor allowing MORE current to flow

Mains Avoid direct working with mains. Use low voltages

Check all leads for: Fraying, Proper clamping, Proper earthing.

Repairing 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]

Environmental issues

Don’t waste power -Turn off 15c per kWh

Use Low power versions of equipment Flat screen Vs old CRT tube TV

Lighting: LED, fluorescent, CFL, Filament

Reduce and recycle, waste considerations!

Avoid hazardous materials Mercury fluorescent tubes & CFLs

Cadmium & lead from re-chargeable batteries



Electrical Hazards & Personal Safety

Used where! Office & home 95%

Laboratory 5% Trailing wires, faulty wires

Mains Avoid direct working with mains. Use low voltages

Check all leads for: Fraying, Proper clamping, Proper earthing.

Repairing 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]


Some examples of electrical hazards

Electronics experiments 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

Hot plates Burns

Electrophoresis High voltages

Trailing Power and Signal wires - Protect & Tidy them up


Sometimes forgotten hazards

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 direct across the heart can

have massive consequences [basis of a heart pacemaker ]

Pace makers Susceptible to strong magnetic fields [NMR! ], Possibly RF & Micro waves interference

Chemical Solvents 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


Yet more examples

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

EHT Static, OK [Very low current, moderate power] nearby Solvents!

Will jump considerable distances,

Beware of capacitors

Power Heating effect in body => internal burns / damage

Contact burns, deep burns & necrosis

Trailing Power and Signal wires - Protect & Tidy them up


Specific Hazards & Personal Safety

Other Laboratory Situations ?

Other Office Situations ?

Other Home Situations ?


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


-


SUMMARY


Summary Awareness

Of the need for electrical safety

Of your personal limitations & permissions

Potential Sources of electrical dangers

Aware of your responsibility to take care of

Yourself and Others

Note Safety Sources for future use

If unsure never be afraid to ask or to say ‘NO’


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


END

Thanks for your attention

basic electrical safety - dublin city university · electrophoresis, dart power lines, capacitors...

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