CHAPTER-2

Report
ELECTRICAL SAFETY
OUTLINE
 The basic effect of electricity on human body
 Ventricular Fibrillation
 Electric shock
 Electric Shock – Treatment
 Important of Grounding
 Fuses and Residual current devices (RCD)
 Work on Electrical Equipment
 Safe values of Voltage
 Electrical Fires / Arcs / Explosions
 Electrical equipment selection
 Maintenance of Portable Electrical Equipment
ELECTRICAL SAFETY
AIM OF THE EXPERIMENT
As is well known, electricity can be dangerous when it is not using in proper
situation. In our laboratory, students must be very careful while they are
working. In this document, they could find some important information
about effects of electricity and the grounding of building.
ELECTRICAL SAFETY
 The Basic Effect Of Electricity On Human Body
 Burns
• Electrical burns result from the heat generated by an electric current
passing through the body
• Electrical burns often have serious consequences: scarring,
amputation, loss of function, loss of sensation and even death.
 Electric Shock
• The minimum current a human can feel depends on the current type
(AC or DC) and frequency.
• Current can cause interference with nervous control, especially over
the heart and lungs.
• Other affecting issues are frequency, which is an issue in causing
cardiac arrest or muscular spasms.
ELECTRICAL SAFETY
 Ventricular Fibrillation
• A domestic power supply voltage (110 or 230 V), 50 or
60 Hz alternating current (AC) through the chest for a fraction of a
second may induce ventricular fibrillation at currents as low as 30
mA. With direct current (DC), 300 to 500 mA is required. If the
current has a direct pathway to the heart, a much lower current of
less than 1 mA (AC or DC) can cause fibrillation. If not immediately
treated by defibrillation, fibrillation is usually lethal because all of the
heart muscle cells move independently instead of in the coordinated
pulses needed to pump blood and maintain circulation. Above
200 mA, muscle contractions are so strong that the heart muscles
cannot move at all, but these conditions prevent fibrillation.
ELECTRICAL SAFETY
 Electric Shock
ELECTRICAL SAFETY
 Electric Shock – Treatment
•
•
•
•
Isolate supply immediately
If you cannot isolate DO NOT attempt to touch casualty
Physically remove victim using non-conducting implements
Check for pulse / breathing, give artificial respiration if necessary
• Briefly, effects of electric is shown in following figure
Zone 1 - No danger
Zone 2 - Usually No effects
Zone 3 – Reversible damage, no fibrillation,
breathing difficulties
Zone 4
5% chance of fibrillation
C1- C2
50% chance of fibrillation after C3
ELECTRICAL SAFETY
 Important of Grouding
• Electrical circuits are consist of power source, connecting cables, electrical
equipment. This electrical circuits in the meaning of general, the gounding of
building must be appointed.
• When a short or lightning occurs, energy flows to the ground, protecting you
from electrical shock, injury and death
• Grounded, permanently connected to earth through a ground connection of
sufficiently low impedance and having sufficient capacity that ground fault
current which may occur cannot build up to voltages dangerous to personnel.
• A system or circuit conductor that is intentionally grounded.
• Prevents conducting parts of equipment which do not normally conduct
electricity from becoming live during faults.
ELECTRICAL SAFETY
 What is Make The Grouding?
•Grounding creates a low-resistance path from a tool to the earth to disperse
unwanted current
•Grounded electrical systems are usually connected to a grounding rod that is
placed 6-8 feet deep into the earth.
•Grounded - connected to earth or to some conducting body that serves in place
of the earth.
No bounding- unsafety
Grounding equi-potential Bonding- safe
ELECTRICAL SAFETY
 Residual Current Devices (RCD) and Fuses
 RCD for Electrical Shocks and Fires
• Compares current in Live & Neutral if different and above a certain
value supply switched off
ELECTRICAL SAFETY
 Residual Current Devices (RCD) and Fuses
ELECTRICAL SAFETY
 Residual Current Devices (RCD) and Fuses
 Fuses for Electrical Circuits
• essential for safety, will cut off supply at a certain current level i.e.
16A, 13A, 5A, 3A, 1A, 0.5A mains supply fuse
• Fuse has a ‘fuseable’ wire element which heats up when current
flows
• Excessive current = excessive heat & wire melts preventing current
flow
ELECTRICAL SAFETY
 Work on Electrical Equipment
•
Switch off using a device that will create an air gap that should not fail
•
Lock off where possible to prevent inadvertent switching ON whilst work
taking place
•
Always test conductors in a reliable way before touching (ie. test the test
device before and after use!)
 Safe Values of Voltage
•
55 VAC systems have not caused anybody to be electrocuted
•
Often referred to as a 110VAC -220VAC centre tapped earth supply (CTE)
yellow coloured equipment
•
Less than 120 VDC considered to be safe
ELECTRICAL SAFETY
 Electrical Fires / Arcs / Explosions
 Fires
• Overheating, arcing & sparking
ELECTRICAL SAFETY
 Electrical Fires / Arcs / Explosions
 Arcs
•
Generated during faults / flashover (Lightning)
•
Very high temperatures / causing burns
 Explosions
•
Flammable substances give off vapours
•
Electrical sparks can ignite (ie. domestic light switch)
ELECTRICAL SAFETY
 Electrical Equipment Selection
 Must be suitable for environment
•
Wet, dusty, flammable gases, mechanical strength, corrosive atmospheres
•
Must be maintained in good condition
•
Failure to select suitable equipment and maintain it often results in incidents
at a later date
 Maintenance of Portable Electrical Equipment
•
Many accidents result from 230 volt portable equipment
•
Pressure Washers / Vacuum Cleaners
•
Most important checks are easy to do!
•
Visual Inspection
•
If insulation is damaged – REPLACE
•
So called ‘Electrical Insulation Tape’ will not provide a sufficient barrier between
you and a potentially fatal electric shock
ELECTRICAL SAFETY
 Maintenance of Portable Electrical Equipment
•
•
Plug
•
Check that only the outer insulation has been clamped / gripped.
Clamping inner conductor insulation will potentially lead to exposure of
live terminals.
•
Is fuse correct rating
•
Check that all 3 pins are present and in good condition
Testing
• Only by a competent person
• Earth bond test
• Insulation test, On-Load Test

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