How to avoid Shock Hazards? Solution File 3

You know, electricity is highly impatient because it is travelling at light speed around 2, 99,460 kilometers in one second. So it is wise to stay away from its path because we cannot move away as fast as electricity. Electric current is the flow of electrons through a conductor when a potential difference develops between the ends of the conductor. Ignorance, mis handling, lack of safety measures can lead to hazardous results like shock or fire. When the conductor offers less resistance, flow current will be fast and if the conductor offers higher resistance, flow of current will be slow. When the current passes through a conductor with higher resistance, heat develops due to friction. Our body, especially the skin is a good conductor for electricity and the skin offers some resistance. So when we touch a live wire, current can easily pass to the earth through the body. Since the skin offers resistance, heat will develop and causes burning. Electricity stimulates nerves and muscles and results in jerking reflex which is considered as shock. We have to understand much in this matter as safety precautions. Let us continue to see this.

Lethal Current

Let us see how current becomes harmful to Human body. Individual body chemistry has significant impact on the effect of current on the body. Some people are more sensitive to current while others are less sensitive. The table below indicates the effect of AC and DC on the human body.

AC                          DC                  Effect
0.3-0.4 mA         0.6-1 mA        Slight sensation
0.7-1 mA              40-60 mA     Pain feeling
10-15 mA              50-70 mA    Voluntary contraction. Cannot withdraw hands
15 – 20 mA           60-100 mA Difficulty in breathing. Pain
100 mA                   500 mA       Heart fibrillation

It is important to note that a low AC current of 15-20 mA across the chest can induce heart fibrillation in some physiological conditions. Ohms law can be used to determine the amount of voltage required to pass 20 mA current through the body. I x R = V.
If the skin resistance of the dry body is 1 M and current is 20 mA then 20 mA x 1 Meg ohms is 20, 000 volts or 20kV.The condition worsens if the body is wet. Skin resistance drops to 20 K or less when the body wet. In this state the voltage required to cause 20 mA current to pass through the body is

20mA x 20K = 400 volts.

If the body has metal objects or in contact with a metal object, the skin resistance drops to 1 K or less. In this condition only 20 volt is sufficient to pass 20 mA current through the chest. A current around 17-20 mA is enough to cause heart fibrillation. In short, the effect of current worsens if the body is wet or in contact with a metal object.

Here are some possible sources of shock hazard and safety measures to prevent it.

1. Bathroom

Bathroom is one of the more likely places where wet people may contact with switches, water heaters etc. Switches, power receptacles, telephone sockets etc should not be installed inside the bathroom. Water heater should not be placed close to water taps and tubs. Telephone plugged into socket is also a source of shock even though it uses DC. Open circuit voltage of telephone line is 48 volts and the ringing voltage is 150 volts DC. Remember an excess of 30 volts AC or DC can cause a shock.

This is not the way to provide a socket in bathroom

2. Extension cord

Most of us use extension cords to power more than one device. Since it powers many gadgets, make sure that its current handling capacity, gauge of wire, strength of contacts etc are suitable for powering many gadgets. Otherwise, due to overloading, contacts and wires heat up and insulation may break. The abberated or cracked wires pose potential dangers. If a cracked point is found, unplug the extension cord and cut the broken point, rejoin and make shock free with insulation tape.

This should be removed immediately

3. Power cords

Power cords used to connect appliances like Mixer, Grinder, TV etc are another source of shock. Now most of the electric appliances use molded cords. If the quality of the insulation cover of the cord is not good, cracks may develop near the plug since the cord bends several times while plugging. Through the cracked insulation, copper wires may expose so that when we plug in the device, there is chance for touching with the cracked point. Remember, a single copper wire can discharge heavy electricity into the body. Check the point of cord joins with the plug. If there is any insulation crack, use insulation tape there or replace the power cord.

This Mixi is dangerous

4. TV

Another possible source is TV and cable. The TV power cord and the Cable inlet are placed nearby on the back side of the TV. Close observation is not possible while inserting the antenna cable into the receptacle. Always unplug the TV while inserting the balloon of antenna into the receptacle. The antenna cable also becomes a source of shock in rainy seasons. If the antenna cable is in contact with trees, electric wires, earth pipes etc during rainy season, there is chance for passing electricity through the cable. So do not try to repair the antenna cable during rainy season without adequate precautions.

Some safety measures

Correct way of wiring

It is better to avoid conditions that may leads to shock hazard. Adequate safety measures should be adopted white repairing, testing or troubleshooting the electric appliances. The following tips will help you to avoid electric shock.

• Always unplug the electrical appliances before opening its cover.

• Wear rubber foot wears while doing electrical works. Rubber is safer than leather since leather holds some moisture in it.

• Check the presence of current in all bare points using a tester before unscrewing the wire contacts.

• Use a rubber sheet on the floor below the work bench so that the feet will rest on it while doing work.

• Wear rubber gloves before working with high volt AC.

• Hand-to-hand current path is more dangerous since current passes through the chest and affects heart. The best way to prevent this is to keep the left hand behind the body or insert into the pocket so as prevent accidental holding of left hand with a metal object while the right hand is in use.

• While installing television antenna or dish antenna, make sure that it is not close to any electric lines or wires.

If a Cap is there, child will be safe

• Close all the unused power sockets with Safety caps to prevent shock hazards. Children may insert metal objects into the sockets while playing.

• Always use switch for controlling the plug sockets. Use 3 pin plugs with correct wiring.

• Make sure that the switch is provided in the phase line. Installing switch through the Neutral line has no use. If body of the appliance makes accidental contact with the phase line, body becomes charged even if the switch in the off position.

Many people don’t care this. But it is a must

DO NOT use multi-way adaptors. Over loading can cause fire. One socket outlet is for one appliance only.

A common view but is dangerous

Install MCB, ELCB etc. in the electrical circuits with proper earthing. Earth pipe should be piled deep into the soil to discharge electricity.

• Unplug all the appliances if they used occasionally.

• ENSURE the switch is in “OFF” position before changing bulbs.

• DO NOT drive nails carelessly on the wall. There may be concealed wiring inside.

• Avoid using handheld appliances when your hand and/or body is wet.

• Check accessories such as plugs attached to appliances for cracks and burnt marks and have them replaced. If undue overheating occurs or burnt marks appear in any electrical appliance, have it checked and serviced.

• Switch off and take the Immersible water heater before using the water.

• Take care while using Washing Machine. Switch off or unplug the machine before removing wet cloths. Use a dry rubber sheet in front of the washing machine to stand on it.

• Never use Mixer near Wash tub in the kitchen.

• Switch off or Unplug Wet Grinder before removing the contents. Do not touch the metal parts while it is operating. Before adding water, switch off the grinder.

• Inside the TV there very high voltage especially in the HT section. So do not touch any parts near the HT section while trouble shooting.

• Unplug the inverter system and switch off its output while removing or cleaning the battery terminals.

• Do not touch the electrical appliances when there is lightning. If possible, unplug all the electrical appliances when the thunder strikes start. Remember, during lightning, very high volt around 5000-50000 volts may pass through both live and neutral lines. Fuse protection is available only in the phase line so when the neutral charges, current passes into the device leading to its permanent damage. This kind of lighting breakdown is common in TV since most people switch off the TV through remote leaving the power cord charged.