Electrical Workplace Safety
Alan Kelly 23rd September 2015
Objectives
To provide an understanding of Electrical terms and
the concepts of electricity
To introduce Electrical Protective Devices and provide
an understanding of their use
To identify the hazards associated with work on or
near “Live” electrical equipment.
To demonstrate the need for and use of Electrical
Safe Operating Procedures.
To Identify the Legislation associated with Electrical
Work and Electrically Operated Equipment.
Statistics
Fatal Electrical Accidents In Ireland
2001–2011
33 Fatalities
In 2005 there were 5 people electrocuted – 2 of these
fatalities were with Low Voltage (LV) = 50 – 1000 volts.
In 2006 there were NO Electrical Fatalities in Ireland
First time since 1936
What is Electricity?
SO
WHAT IS IT MADE
OF!!!
Electricity is made up of a range of
components e.g. Voltage – Current –
Resistance – Power.
What is Electricity?
Aluminium Atom
13 Electrons
29 Electrons
Nucleus
Electricity is the moving of Electrons in a wire or
conductor and the consequence of this movement.
Voltage
Is the pressure which pushes the
electricity through the system from the
Generator to the Customer.
Measured in VOLTS
Symbol = V
230 Volts (230V) 10kV/ 20kV /400kV
Italian Physicist Alessandro Volta
Voltage
Voltage
Voltage = Pressure – Measured in Volts –
Symbols V, U and EMF
Pressure gets electrons to move
Levels of Pressure
230V = level of pressure
400V = higher level of pressure
1000V = higher level again.
Voltage Levels
Extra Low Voltage
= < 50Volts
Low Voltage
= 50 – 1000Volts
Medium Voltage
= 1kV – 38kV
High Voltage
= 38kV- 400kV
Current
This is the Rate of Flow of electricity
which flows through the system from
the Generator to the Customer.
Measured in Amps
Symbol = I
e.g. 20 Amps
20A
20mA (mA=1/1000A)
French Physicist Andrea Ampere
Current
Current = Movement of Electrons
Current measured in Ampere’s or amps
Symbol = I or A
Types of Current
DIRECT CURRENT (DC)
ALTERNATING CURRENT (AC)
DC
Direct Current
CURRENT FLOWS IN ONE
DIRECTION
LIKE A BICYCLE CHAIN
AC Alternating Current
CURRENT FLOWS IN BOTH
DIRECTIONS
LIKE A HAND SAW
ALTERNATING CURRENT
ALLOWS THE USE OF
TRANSFORMERS WHICH
MAKES THE TRANSMISSION
OF POWER MORE EFFICIENT
400
Voltage
Voltage
Voltage Current
Voltage
Current Current
300
Ic
Ic
Current + Ic
Current + Ic
200
100
Volts
0
0
0.2
0.4
0.6
0.8
-100
-200
-300
-400
Time
1
1.2
1.4
1.6
1.8
2
Frequency
Frequency of a system = Number of
cycles per second
In Ireland this = 50;
It is measured in Hertz (Hz)
50hz
Stroboscopic Effect
May cause rotating objects to appear
stationary or at least moving slowly
Fluorescent lighting – Problems
Solution – Filament lighting adjacent to
machine
Solution – Supply each row of lights from
separate Phases
Effects Of Electric Current
Heating Effect – caused by friction
Examples – Kettle, Cooker, Space Heater, Immersion & Light bulb
Effects Of Electric Current
Magnetic Effect
Voltage
Examples – Motors, Transformers, Relays, Contactors & RCD’s
Resistance
The extent to which the Flow of
Electricity is impeded in a circuit.
Measured in Ohms
Symbol = Ω (or R or Z)
e.g. = 200 Ohms,
200 Ω, 2M Ω
German Physicist
Georg Ohm
Resistance
Resistance = Opposition to current flow
Resistance due to type of
material & CSA
Higher Resistance due
to smaller CSA
Measured in Ohms - Symbol = R or Ω
THE ###
ELECTRON WON’T
MOVE
THE ELECTRON
WILL MOVE
EASILY
THE ELECTRON
WILL MOVE, BUT
WITH DIFFICULTY
FRICTION
HEAT
EASY
ATOM
INSULATOR
•
•
•
•
CERAMICS
P.V.C. (Plastic)
RUBBER
OIL
ATOM
ATOM
CONDUCTOR
RESISTOR
•
•
•
•
•
•
•
•
•
•
GOLD
SILVER
COPPER
ALUMINIUM
MERCURY
TUNGSTEN
STEEL
NEON GAS
SALT WATER
CARBON
Power
Is the rate at which Current flows at a
given Resistance and Voltage
Power
=
Voltage x Current
Measured in Volt-amps / Watts
e.g. 10 VA
15 kVA /kW
Types of AC circuits
Single Phase
The transfer of electricity using Two Wires
Three Phase
The transfer of electricity using 3 or
4 wires.
Switching “On” of Electrical Circuit
Switch
PH
Fuse
N
Fuse is in circuit to protect the conductors (wires)
Switch is in circuit to control the flow of current
Switching “Off” of Electrical Circuit
Switch
PH
Fuse
N
When ever current flow is interrupted you get an ARC or SPARK due
to the Voltage trying to push electrons across the gap
Switching “Off” in Explosive Atmosphere
The use of electricity can generate hot surfaces or sparks which
can ignite an explosive atmosphere
Dust
Switch
PH
Fuse
N
Explosive Atmosphere = Work Areas where Dust (flour mill), Gases,
Paint Spray or Vapours (Petrol Station) exist.
IP Rating
IP rating of equipment refers to the electrical
equipments ability to withstand the ingress of
either liquids or solid bodies
IP 56 ; In this example the Ingress protection
offered by this equipment is given by the two
numbers.
The first number refers to the protection
against the ingress of solid bodies.
The second number refers to the protection
against the ingress of liquid.
IP Rating
Example of IP rating
IP45 = Protection against normal dust and
hosing and is suitable for Dairies.
IPX4 = only protected against hosing is
given
Electrical hazards associated with electrical
systems and equipment include:
• Electric shock
• Burns sustained at the point of accidental
electrical contact, or due to arcing from
high voltage conductors
• Fires caused by overheating or ignition of
explosive atmospheres
• Secondary injuries as a result of muscle
spasms during shock or, for example,
falling from a ladder after a mild shock.
The Electrical Circuit
Electrical
Appliance
Frame is Live
Fau
lt
Live
L
O
A
D
Electricity
Supply
Neutral
Main
Earth
Probably a FATAL accident
General Mass of Earth
The Electrical Circuit
What can be done to try to prevent the electric shock?
We can “Earth” the appliance or machine
We can install a protective device (fuse or mcb)
Electrical
Appliance
Fau
lt
Live
Fuse/mcb
L
O
A
D
Electricity
Supply
Neutral
Neutralising Link
Main
Earth
Earth Rod
General Mass of Earth
The Electrical Circuit
What can be done to try to prevent the electric shock?
Protective Device Operates
Electrical
Appliance
Fau
lt
Live
L
O
A
D
Electricity
Supply
Neutral
Main
Earth
The larger current flowing blows
the fuse and the appliance frame
is no longer Live
General Mass of Earth
Earth Rod
The Electrical Circuit
Another device used to prevent electric shock is the RCD
RCD/ELCB
Electrical
Appliance
Fau
lt
Live
Electricity
Supply
Fuse/mcb
R
E
L
A
Y
L
O
A
D
Neutral
Main
Earth
Earth Rod
General Mass of Earth
The Electrical Circuit
In the event of an Earth Fault the RCD trips the circuit faster than the fuse/mcb
Electrical
Appliance
RCD/ELCB
Fau
lt
Live
Electricity
Supply
Fuse/mcb
R
E
L
A
Y
Test
Button
L
O
A
D
Neutral
Main
Earth
The RCD uses the imbalance between
the current in the phase and neutral to
identify that there is a fault.
General Mass of Earth
Earth Rod
RCD
T
The test button
on RCD’s installed
in this country are
marked with the
letter “T”
It is possible
to purchase
Plug-in RCD’s
Circuits feeding ‘plugged-in’ appliances, showers
and immersions must be protected with an RCD.
Typical domestic distribution board
RCD
Recommended to test the RCD twice a year,
probably best at time change in spring & Autumn
Typical tripping times expected using RCD tester
=
0.30 secs at 30mA
0.15 secs at 60mA
0.04 secs at 150mA
Testing regime depends on Installation
Working on Electrical Equipment
Electrical
Machine
Live
L
O
A
D
Electricity
Supply
Neutral
Main
Earth
Probably a FATAL accident
General Mass of Earth
Electrical Hazards
Electric
shock – electrocution
Caused by simultaneous contact of two parts
of the body with either:
Phase (live) and Neutral (Single Phase System)
Phase and another Phase (3 phase System)
Phase (live) and Earth.
Effects of Electric Shock
Involuntary
muscular contraction
Respiratory paralysis (Asphyxia)
Surface and deep tissue burns
Lack of Oxygen in blood,
Loss of consciousness
Ventricular fibrillation of heart (spasms)
Death in 3-7 minutes if no intervention
(CPR).
Effects of Electric Shock depend on:
Level
of Voltage
Duration of shock
Body Resistance
Insulating material (e.g. shoes, gloves)
Path of current
Person’s health (e.g. heart condition)
Age.
Effects of Electric Shock on
Nervous System
Threshold of perception
Mild shock
Threshold of “let-go”
Very severe shock
Fatal
0.5 - 2 mA
2 - 10 mA
10 - 30 mA
30 - 50 mA
> 50 mA
230 volts will result in a current of
approx. 80-240 mA through the body
Fuses & MCBs do not protect against
electrocution.
Electrical Burns
Flash
- radiant heat
Spatter
with molten
copper
Burns
at entry and
exit points of current
from body.
Protection Against Electric Shock
Proper Earthing and Bonding
Use of Earth Leakage Circuit Breaker (RCD)
Safe System of Work (Lockout/Tagout)
Use of Insulated Gloves,
Use of Insulated Footwear or Insulated Mat
Use of Double Insulated Work Equipment
Regular Inspection & Testing of Installation
and Equipment
Electrical Device Safety
1. Properly fitted plug tops
2. Plug tops should have the correct fuse
3. Routine Safety Testing
4. Do not place fluids on top of electrical devices
5. Do not plug in equipment when you have wet hands
6. Report all faults
7. Report all frayed cables, broken plugs or any plugs
that feel warm.
The Electrical Circuit
Another Fault that can occur is what’s called a Short Circuit.
This is a very low resistance connection between the phase/live and
neutral in a single phase system or between phases in a 3-phase system.
Live
Fuse/mcb
L
O
A
D
Electricity
Supply
Neutral
Main
Earth
The high level of current
flowing as a result of the fault
operates the protective device
General Mass of Earth
Earth Rod
Electrical Hazards
Short
Circuit
Explosive effect of discharge.
Fire.
Pressure Wave
Shrapnel
Sound
Protection Against Short Circuit
Use of Proper Circuit Protection.
Use of Insulated Tools
Adequate information about the risks
Use of Full Face Visor & Helmet,
Use of appropriate Arc Resistive Overalls
Use of suitable barriers & screens
Accompaniment by second person
Effective control of work area
Electrical Faults
If an iron, washing machine, etc.,
causes a fuse to blow or MCB to
trip...
Always isolate the appliance
before restoring the power supply
Always identify the fault before
reconnecting the appliance
The Same applies to all electrical
equipment.