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.

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.

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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.

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Electric Shock

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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

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Zone 1 - No dangerZone 2 - Usually No effectsZone 3 – Reversible damage, no fibrillation, breathing difficultiesZone 4 5% chance of fibrillation C1- C250% chance of fibrillation after C3

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.

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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.

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No bounding- unsafety Grounding equi-potential Bonding- safe

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

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Residual Current Devices (RCD) and Fuses

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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

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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!)

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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 Fires / Arcs / Explosions Fires• Overheating, arcing & sparking

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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)

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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 dateMaintenance 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

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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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