Electrolesk A Guide to Practical Electrical Installation Work.

Safety Sign

Electrical Safety vital for Electricians

Anyone working with electrical equipment or installation work, should be careful enough avoiding getting an Electric Shock. This is called Electrocution. An electric shock can occur if a person becomes a part of a Electric circuit. The magnitude and the duration of the current flow through the body are the main factors for the seriousness of Electrocution. One can feel even a current of 5mA [5/1000 Ampere] entering through the hand.Even a 1mA current through the heart can be fatal. AC Currents in the range of 100mA are lethal if they pass through sensitive portions of the body. An electric shock due to 50 /60 Hz AC current can be fatal than a current of the same magnitude from a DC source.

If by accident, one touches a live conductor by one hand and if the other hand is placed on an earthed metal object, then a current can run through the body, entering from one hand ,passing through the heart area and leaving from the other hand to the earth,which can be most dangerous.


The amount of current passing through the body mainly depends on the body resistance . When the body is wet or perspired, even a small voltage will make more current flow through the body. Notice, how the current decrease with the increase of the body Resistance from the Ohms Law,

Current = Voltage / Resistance

Table below indicates the current flow through the body when the body resistance changes.

Voltage-Volts AC Resistance- Ohms Current-mA Effect on person
230 100 2300 Hazardous
230 1,000 230 Hazardous
230 10,000 23 Hazardous
230 100,000 2.3 Hazardous
230 1,000,000 0.23 Threshold
230 10,000,000 0.023 Safe
230 100,000,000 0.0023 Safe

 

Skin Resistance of Humans changes under different conditions of the body.

Skin resistance -Dry - 100,000 Ohms

Skin resistance -not Dry or Wet - 5000 Ohms

Skin resistance -Wet - 1000 Ohms or Less

 

The Effects of magnitude of Current through Human Body

A current of 1mA or less through body- Person do not feel the effect

A current of 5mA or more through body- Person experiences shock

A current of 10-15mA through body- Local muscle contracts. A person holding a live wire or a an object will by hand not be able to release the grip of the hand holding the live wire or object.

A current of 50mA-100mA through body- Ventricular Fibrillation of the Heart occurs, which means that the normal rhythm of the heart's pumping action stops and the pulse disappears.

A current of 100mA or more through body- Damage to body tissues occur.

 

The Effects of duration of Current through Human Body

The maximum safe duration of dangerous current for Humans is about 3/10 th of a second or 300 mill Seconds. Anything above this time will be dangerous.

 

Electrocution leads to

[1] Ventricular Fibrillation

This is the malfunctioning of co-ordination of the Heart's pumping action.

[2] Respiratory Arrest

Currents of 1000mA or above through Lung area or Head causes Respiratory malfunction

[3] Asphyxia

When current flaws through the arm, the muscles of the forearm contracts and stops the ability loosening or manipulating the grip of the fingers and palm area thus the person under shock is unable to control the actions of the arm at his own will.

 

The early, Screwdriver type voltage testers with a neon bulb were connected with a Mega ohms valued resister in series that limited the current flow through body to a safe value but gave a Glow in the Neon light when the tip of the tester touched a live main wire. Mainly, a person’s body has to get earthed for a current to flow through, after entering, say through one’s hand and leaving through the foot to the earth.

 

One can increase the overall resistance of the body by means of wearing protective wear, to a value of some Mega Ohm range, so that currents of Micro Ampere range only will flow through the body when the person works with low voltage[50 to 600 V -AC ] live wires.


That’s how some electricians work on live conductors while wearing specially manufactured rubber boots and gloves.

 

 

To avoid Electric Shock, the following precautions can be taken by a person working on any Electrical work.


- Make a thorough Visual Inspection on the area of work , one intends to do , taking into consideration, the existing condition of the Electrical installation, the placement of Main Switch positions and the equipment. This way, one can asses the condition of the Electrical Installation.


- Poorly maintained Electrical Installations are hazardous and specially in rainy weather and in wet conditions


- Make sure to isolate power to the circuit or equipment by disconnecting [ switching off Main Switch/ MCBs etc.] Mains Power.


- Keep a Warning displayed at the disconnected Main switch so others will know that the mains were knocked off purposely for maintenance work.


- Check with a Test Lamp or with a Voltmeter whether the power has been disconnected.
- Wearing Rubber soled shoes or boots will be safer for a person while doing electrical related work.


- Take extra precautions when working in wet or damp environment.


- Use proper tools specified for Electrical work with good Insulation quality.


- Concentrate on the work mindfully till you finish the relevant electrical work. Electricution is a serious affair, which will happen only in seldom, but being knowledgeable on the subject is an asset to everybody.

 

What action to be taken in the event of a person gets electrocution.

Disconnect the power supply immediately.

Never try to touch the person to dislodge him from the live conductor or equipment.


In a worst case, with a dried wooden pole [ or any other insulated material you can find ] , try to push the person from the live conductor or equipment.


Once the person is removed from the power source, immediately take him to the nearest hospital.

 

To minimize the risk of getting Electrocution, special power distribution methods has been in use in some countries and also Residual Current Devices which [ for households which operates from 30mA fault current setting] has been incorporated in final circuits so that the power gets disconnected if there is a current flow to earth.