How you get electric shocks

I have sent a lengthy article to this blog some time back on how a person can happen to get electrical shock. However, some readers complained that it was too long that they have difficulties finding what they want to read about. Therefore, I have decided to write a few short articles on subtitles covered by that post for the benefits of casual readers who are looking for only certain very specific issues. This post is the first of those subtitles.

Look at the four beautiful diagrams that I just created below.

Diagram 1 – Touching live electrical wire and the neutral wire



THE SIMPLE LOGIC OF ELECTRIC SHOCKS

Electric shock happens when a certain amount of electrical current happen to flow through a person’s body for whatever reason. The human body has not been designed to conduct electricity above a certain current level or miliamperes. The above-mentioned post on electric shock protection gives a detailed description on the levels of current that can cause injuries and electrocutions. You can read it here, ELCB - Home Electrical Shock Protection, if you wish to know them in more details.
What happen when the electrical current flow through the body? At a lower level, the current interferes with the nervous system. That is why when someone accidentally holds a live wire with her hand, she may not be able to let go of the wire. In fact, her fingers may even grip the live wire tighter, resulting in a much better contact between the hand and the wire. This will result in lower contact resistance that will further increase the current flow and therefore more serious injuries. If you visit this post, Electrical injury pictures, you can see the pictures of how serious the electrical injuries can be.

The higher the shock current, the more severe the injuries

If the shock current is higher, then the body tissue where the current flows will get damaged. The higher the current, the more serious the damage. At 10mA, the victim may still be able to control his arm and instinctively release the electrified object or wire he is holding. However that is about the maximum shock current that he can handle. If the shock current is higher, he would lose control of the arm. The hand grip on the tool may get stronger, resulting in higher current flow.

At 100 mili-amperes (that is 0.1A), the victim faces a certain death if he sustains that level of shock current flow for 2 seconds or more.

The degree of injuries depends on which body parts the shock current flow through

The path where the shock current travels through the body also will have some effects on how serious the injuries can be. If a person touches a live wire by his right hand while standing on a grounded metal part, the electric current flow through from the live wire through the hand, the arm and shoulder, the chess, legs and down to the metal part. In this case, the current can damage the victim’s heart while flowing through the chess. At 30 mili-amperes, the victim may even stop breathing (respiratory paralysis).

The higher the voltage, the more serious the injuries

The higher the voltage, the more serious the resulting injuries. At 600 volts, the electric shock current can be as high as 4 amperes. This level of current can seriously damage the victim’s heart and other internal organs. The skin where the body makes contact with the live wire can be burned. The tissue damages are so serious that a limb on the path of the flow of the shock current can come off the victim’s body.

The longer the current flow through the victims body, the more serious the injuries

As I said above, at 100 mili-amperes, the victim faces a certain death if that level of current continues to flow through the body for more than 2 seconds. This is very useful information for those who work on live electrical parts either by occupation or just a do-it-yourself (DIY) working on a live house wiring.

The way you stand or the way you access the live parts should be in such a way as to make the duration of contact with the live part as short as possible in the event of accidental contact. Of course, you must at all times de-energize the faulty part before starting on the repair works. However this advise very often are just ignored by some people either because they feel they are skilled enough to work on live parts, or they just don’t bother much with their own safety.

Whatever the reasons are, you can actually position yourself such a way that at the moment of accidental contact, your reflexes will cause your body to break contact immediately. This quick contact break will mean life or death.

About a week ago, a news broke out about a fatal accident involving electrical works has occurred at a project not far from the jobsite I was working on. After some checking, I finally found out what actually has happened that led to the immediate death of the worker. Actually he was trying to cut an insulated electric wire inside a recently completed building. The building has just been handed over to the client and most of the tenants were busy with their own renovations works before they actually move in to the new place.

So the worker was trying to cut a live internal wiring that was supposed to have been dead and isolated by a colleague. As it happened, his colleague isolated a wrong circuit breaker on the electrical DB.

We can talk about isolation procedures in other posts. What I wish to point out here is the way the tool is handled in the case of a wire cutting. The cutter is held with the palm of the hand and a few fingers forming a strong grip. This form of hand action is difficult to let go in the case of an accidental contact.

Some other forms of hand action will more likely result in breaking contact by the body reflexes as the electric shock is sensed. One example is the turning of a termination screw at a circuit breaker terminal using a screwdriver. This sort of issue can be quite subjective and different persons may handle a tool a bit differently. But I think all experienced technicians agree that there is a room there to make the injuries less severe if it has to happen.

The higher the skin contact resistance, the lower the shock current

What does this mean in layman terms? I know these electrical terms can be intimidating to some people. However, electrical safety should be an issue for concern to everyone who use electricity on his or her houses or at their workplaces.

Look at Diagram 1 again. In this case, the girl is almost touching two electrical wires. When both hands touches the wires, the shock current can travel from the left hand holding the red live wire to the right hand holding the black neutral wire.

How much current will actually flow?

That depends on three things. 1. How many volts of voltage at the red live wire; 2. How many volts of voltage at the neutral black wire; 3. How much resistance is presented by the body against the current flow from left hand to the right hand.

Let’s answer this question one by one. For question 1, if you live in London, that voltage may be 220 volts. (Note: Do not get confused by the “volts” terminology. A volt is like speed. 3A or 3 amperes is like 3 meter per second, not like 3 apples per basket.) If you live in Kuala Lumpur, that voltage level may be 240 volts.

However if you live in Los Angeles, your house power sockets will have 110 volt supply. So the red wire there will have 110 volts of voltage.

For question 2: The voltage there will probably be zero volts in all the three cities mentioned above. However there are situations where the voltage at the neutral wire there is not zero. So the neutral wire is not always safe. Always keep this in mind when working on electrical wiring or equipment.

Before we go to question 3, let us do a little bit of calculations first. Since the voltage at the left hand is 240 volts (assuming you are visiting Kuala Lumpur), and 0 volt at the right hand, then the voltage different between the two points is

240 – 0 = 240 volts.

An electrician will call this a 240 volts of potential difference. If the black neutral wire is injured somewhere on the floor, and it touch a live faulty equipment which is at 200 volts, then the potential difference is

240 – 200 = 40 volt, which is a lower value (and hopefully less dangerous).

So how much shock current will flow through the girl’s body if the potential difference is 240 volts (assuming 240 – 0 volts)?

That will depend on how much resistance is presented by the girl’s body against current flow from the live wire and the neutral wire.

So how much is the normal body resistance? This is actually Question No 3 above.

Well, when the skin is dry, the body can present a resistance as high as 100,000 ohms (that is 100 kilo-ohms) against the current flow.

The magnitude of current is lower as the body resistance goes higher. So in this case, the magnitude of the shock current will be:

Shock current = voltage difference divided by body resistance
= 240 volt / 100,000 ohm
= 0.0024 ampere

That is 2.4 thousandth of an ampere of electric current flow, or 2.4 mili-amperes, or 2.4 mA.

How much damage will this amount of current do to the human body? Again you can see the detail list of the injuries in the above-mentioned post. However I listed a few of them here for easy comparison and to help you appreciate the size of this shock current from the viewpoint of injuries that it can cause.

At 1 mA – a normal person would feel a slight tingling sensation.

At 5 mA - A light shock will be felt, but most persons will be able to “let go”. Not a painful feeling, but definitely disturbing. However, a strong reflexive movement by the victim can cause further accidents and other type of injuries.

At 6 to 30 mA - The victim can be paralyzed, or the muscles will freeze (will not be able to release a tool, wire, or other object).

Painful, and my not be possible to let go.

At high voltage (above 600 Volt), this current can already cause severe burns.

As you can see above, at 5 mili-amperes or below, a normal person should still be able to let go the electrified object the he accidentally came into contact with. So a person with dry skin would be less likely to suffer severe injuries if he accidentally comes into contact with a 240 volts live wire. A 110 volts domestic voltage at American house will be less than half of that shock current, so it would be safer theoretically (the American safety follows a different standard so we cannot really compare them apple to apple).

Now let’s see what will happen when the skin is wet. The wet condition can result in a very much lower skin resistance to electric shock current. It can be as low as 1,000 ohms. Therefore the shock current is

Shock current = 240 divided 1000
= 0.24 ampere, which is 240 mili amperes!

From the list that I copied above, at 30 mA the victim would surely not be able to let go of the electrified object he was holding. Therefore the shock current through the body will eventually rise to the maximum that is limited by the body resistance which is 240 mA.

So the victim can suffer a maximum level of injuries. The list on the other post says:

(At 75 mili-Amperes and above – The victim undergo ventricular fibrillation (very rapid, ineffective heartbeat). This condition can cause death within a few minutes. The only way to save the victim is by a special device called defibrillator.

So there you have it. The comparison of the level of resulting injuries between the lowest and the highest skin contact resistances.

BASIC CASES OF ELECTRIC SHOCKS

I started out this post with the intention of explaining about how someone can get electric shocks. But I seem to have spent this far explaining more on the logics of electric shocks.

However, the understanding of the working principles, or the mechanics, behind these accidents will be more useful to you in achieving the most important objective: that is to prevent all serious injuries that result from electrical shocks.

It would be nice to be able to prevent electrical accidents altogether. However as any construction man would testify, it is near to impossible to prevent accidents at construction sites.

The rough environment that a temporary electrical installation is subjected to, the nature of the electrical users at the jobsite, and the difficulties faced by persons responsible on electrical safety on large construction sites to ensure adequate level of safety habits are actually practiced throughout the construction grounds and floors. These three constraints make it near impossible to totally prevent electrical accidents on large construction sites with thousands of workers, especially those with small site areas such as high rise construction at city centers.

What we can do is to minimize the degree of electrical injuries when they do occur.

However, electrical accidents at home or office can still be prevented totally. That is my opinion.

Now THE how to get electric shock No 1. As shown in Diagram 1 at high up in the beginning of this post, that can happen when two locations on the human body came into contact with conductive parts at two different voltages. I have used this diagram to explain the whole upper part of this post above. So that should be enough.

Diagram 2 -Touching live and earth wire


In this case, the right hand came into contact with the earth wire instead of the neutral wire shown in Diagram 1. The result can be similar. I said “can be” instead of “will be”. Why? Because in this case, the live red wire can be installed with an electric shock protection device that will sense this shock current.

The devise is the ELCB (earth leakage circuit breaker). Other names are also used to explain this function in an electrical installation such as RCD (residual current devices), GFCI (ground fault circuit interrupters), etc. Read this post ELCB Circuit to know more how this device functions.

Diagram 3 – When the hand touches a live wire and the person is not separated at the feet from the ground with purpose-made electrical insulation means like rubber shoes, the rubber mat in front of the switchboards in electrical rooms, etc.



Diagram 4 – When there is simultaneous contacts with fault electric motors and ground.



The electric motor can be any electric equipment or appliances. The same process of electric shock current flow will happen.

There are more points that I wish to write down here. However it’s already almost three AM and I have to go to work tomorrow. So I will continue this some other time, in another post.

Stay safe. Electricity kills.

RELATED ARTICLES: a) Home electrical wiring, symbols and checking;

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ELCB circuit

The diagram below shows how a single phase ELCB circuit looks like. However, before I get down to explain more, please take note that I am using the name ELCB as a generic name, just like a circuit breaker.

1. ELCB is a short for Earth leakage Circuit Breaker. When it first came to be used, the devise is actually a voltage-operated device that was designed to detect a current leaking through the earth path of electrical equipment and appliances. I used to see the actual circuit during my college days, but I have to dig it up and redraw it for uploading. You will see it in one of my future posts.
2. The circuit that you see here is actually an RCD (residual current devise), or RCCB (residual current circuit breaker). It is based on the principle of magnetic core balance and the trigger core is current operated instead of voltage operated as in the earth leakage circuit breaker.
3. In terms of performance, the residual current circuit breaker is definitely better. The performance of the old ELCB did not have any problem, but the residual current device can do the same and more.
4. I cannot remember when the residual current circuit breaker actually took over the whole wiring scene, but I cannot find the earth leakage circuit breaker in actual installation anymore. Everywhere that I know is unsung the RCD, but in the field the terminology used have not changed at all. Everywhere and in all design drawings the name ELCB has not been changed. Only some textbook and in the academic classes the RCD or RCCB terms has been used. Therefore, the convention has not been changed. That why throughout this blog I will keep on using the ELCB for this earth leakage device.
5. Originally ELCB was designed to detect earth leakage current and to disconnect the circuit immediately when a certain limit was crossed. Now RCD does the same. Therefore, the general practice to still call the residual devise an earth leakage circuit breaker is still correct. It is still an ELCB by purpose and function even though the internal circuit design has actually changed.
6. However, in certain scenarios both ELCB and RCD names need to be used for clarity. The discussion on internal circuit design of the device like now is one of the scenarios. That is why I will use the two names interchangeable in the following part of this post.
The picture below shows a typical single-phase double pole ELCB circuit. I think it is better to first explain the components of the circuit one by one and explain the how the circuit works afterward.

Diagram 1 – Typical ELCB circuit



a. The supply coil, the neutral coil and the search coil all wound on a common transformer core. On a healthy circuit the same current passes through the phase coil, the load and return back through the neutral coil. Both the phase and the neutral coils are wound in such a way that they will produce an opposing magnetic flux. With the same current passing through both coils, their magnetic effect will cancel out under a healthy circuit condition.
b. In a situation when there is fault or a leakage to earth in the load circuit, or anywhere between the load circuit and the output connection of the ELCB circuit, the current returning through the neutral coil has been reduced. Then the magnetic flux inside the transformer core is not balanced anymore. This unbalanced flux is what we call a residual flux.
c. The residual flux will be detected by the will cross the winding of the search coil and produce a voltage that drives a current inside the wiring of the trip circuit. It is this current that operates the trip coil of the circuit breaker. Since the current has been driven by the residual magnetic flux (the resulting flux, the net effect between both fluxes) between the phase and the neutral coils, it is called the residual current devise. With a circuit breaker incorporated as part of full circuit, it is called residual current circuit breaker (RCCB) or residual current devise (RCD).
d. The incoming current will come through the circuit breaker first before going to the phase coil. The return neutral path passes through the second circuit breaker pole. During tripping when a fault is detected, both the phase and neutral connection is isolated. The circuit breaker can also be used to manually ON or OFF the circuit.
e. The load circuit is not part of the ELCB circuit. However, notice the earthing symbol at the load circuit. That is the earthing connection from the exposed metal parts of the electrical equipment or appliance to the electrical earth. This earthing connection will allow the ELCB fulfill its purpose of being in the electrical circuit. You can have a good operational ELCB unit properly installed and wire at the electrical panel, but if the earthing connection is broken or missing, the ELCB will not trip during an actual earth leakage situation.
f. The test pushbutton and the test resistor are arranged to provide a test function for the ELCB circuit. This part of the circuit bleeds away a fraction of the running current from the phase coil. So the neutral coil current will be higher the phase coil current. Therefore, a residual current will be generated in the trip circuit and trips the circuit breaker.

The above trip simulation tries to check the health of the ELCB circuit. In it works. However, it does not test the complete operation of the protection system that the ELCB is supposed to serve.

Read how you can get electric shocks here. Other related articles: a) Home electrical wiring, symbols and checking;

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ELCB – Home Electrical Shock Protection

This post discusses in some details the home electric shock protection, and the ELCB as one of the most important components in the system.
I have also added into this post some details on the dangers of electric shocks and the type on injuries may be suffered by the victims. However, if you like you can also go straight to the article on shock injuries. But if you are actually looking for electrical injury pictures, just go straight there.
This is a long post, so I noted below the content list to guide you as you scroll down to the bottom.

Content:

A. What is an ELCB
(Image: picture of home electrical panel)

B. Why do we need an ELCB
(a) The danger of electrical shocks
(b) Injuries caused by electric shocks

C. How electrical accidents (i.e. electrical shocks) happen
(a) General
(b) How house wiring works
(c) How electrical shocks happen

D. The working of ELCB
(Image: typical ELCB circuit)
(a) What does ELCB need in order to operate properly
(b) Grounding

E. Other variations of ELCB
F. How to test ELCB

A. What is an ELCB

The earth leakage circuit breaker or commonly called the ELCB is located inside the home electrical panel or distribution board. This component of the home electrical installation is designed to detect any leakage of electrical current.
This so-called leakage current occurs when there are some defects in the performance of some part of the installation, which can be caused by faulty components or by injuries to the insulation of the wiring, cables, electrical appliances or other accessories such as the switches and socket outlets.
When the current leakage occurs, the ELCB then trips the electricity supply within a fraction of a second of the leakage being detected, before the magnitude of the current reaches a lethal level.
Therefore any possibility of serious injuries due to electric shock to persons who are in contact with the electrical installation at that particular moment is minimized.
The use of ELCB in house wiring is required by law and omitting it is a serious offence.
Shown below is a picture of a typical home electrical panel. The ELCB is the second component from the left, with the letters CLIPSAL on it. The left-most component is the main switch (in black color), while all other components on the right of the ELCB are the outgoing circuit breakers.

B. Why do we need an ELCB

(a) The danger of electrical shocks

Whenever you use electrical appliances and equipment whether at home or at work, there is always a risk of hazards, especially of getting electric shock.
The refrigerator, the washing machines, the space heaters or even electric toys and entertainment equipment; they are all electrical hazards to users and household members at some point in appliances’ life cycles.
Eventually these harmless machines and toys will become liabilities and accidents waiting to happen. You need to watch out for them.
Of course, workers face a much higher risk of electrical injuries and electrocution and this not only apply to workers who use electrical tools.
Haphazard site work conditions usually have temporary electrical supply cables and electrical extension cords running all over the place on the work floors. All these situations present very high risks of electrical accidents to all workers regardless of their trades and disciplines. These are how you get electric shocks.

Workers who work on live electrical equipment and electrical distribution and wiring may find the second part of this article too familiar and therefore an unnecessary reminder for them. However, accidents usually happen when we least expect it. Ever heard of a circus tiger killing its own master?
So do not take shortcuts when safety procedures at work are concerned. All safety procedures are there for a reason even if sometimes we are all very reluctant to follow or even to accept some parts of them.
Lastly, let us not forget about the creative do-it-yourselfers. From statistics released by many organizations, many house electrical fires have been a result of imperfect electrical jobs carried out by the not-so-skilled DIY hobbyists. You can bet electrical shocks and electrocutions are part of the lists.

(b) Injuries caused by electric shocks

Let us go directly to what actually happens to a human body when electric current flow through by accident (or by intention…).

Effects of the shocks

Listed below are the effects of electric shocks starting from the lowest amount of current flow to the highest for a duration of one second at typical household voltages.

1 mA - A normal person will feel a slight tingling sensation.

5 mA - A light shock will be felt, but most persons will be able to “let go”. Not a painful feeling, but definitely disturbing. However, a strong reflexive movement by the victim can cause further accidents and other type of injuries.

6 to 30 mA - The victim can be paralyzed, or the muscles will freeze (will not be able to release a tool, wire, or other object

Painful, and my not be possible to let go.

At high voltage (above 600 Volt, this current can already cause severe burns)

Women start to suffer the effect at lover current levels (6-26mA), while men can sustain until a bit higher (10 to 30 mA)

30 mA - Will cause respiratory paralysis
(The victim stops breathing for a period of time)

30 mA - This is the most sensitive rating of Earth Leakage Circuit Breakers (ELCB) normally installed in residential home in this country.

50 to 150 mA - The victim get an extremely painful shock.
The breathing stops (respiratory arrest).
Severe muscle contraction: flexor muscles may cause holding on, extensor muscles may cause intense pushing away.
Death is possible.

(At 75 mili-Ampere and above – The victim undergo ventricular fibrillation (very rapid, ineffective heartbeat). This condition can cause death within a few minutes. The only way to save the victim is by a special device called defibrillator.)

1 A and above - Uneven heartbeats occurs (Ventricular fibrillation).
The muscles will contract.
Damage to the nerves.
Death is likely.

4 A - The victim gets heart paralysis, which means the heart stops pumping.

(Highlight: How much is 4 amperes? If you connect a 1KW portable space heater to a wall socket outlet, and your house supply from the electricity company is 240 Volt, then that’s about 4.1 amperes running inside the wires from the socket to the space heater.)

5 A and above - Human tissues get burned.

10 A and above - Cardiac arrest and severe burns.
Death is probable.

Note: The above medical data has been obtained from the National
Institute for Occupational Safety and Health (NIOSH)

13 A - The lowest current a typical plug fuse will blow in a socket – plug supply connection.

15 A - Lowest level of current a normal circuit breaker or fuse will trip at a home distribution board, or a house electrical panel.
Further explanations on the electric shock injuries
The higher the current, the longer the time of the shock current, the more severe the injuries

(a) As you can see above, the higher the current that flow through a human body, and the longer it flows, the more serious the injuries.
If the shock is short in duration, it may only be painful. A longer shock (lasting a few seconds) could be fatal if the level of current is high enough to cause the heart to go into ventricular fibrillation.
100 mili-ampere current flow (that is one tenth of an ampere, or 0.1 Ampere) through the body will kill a person in just 2 seconds. Maybe he does not die immediately, but death is almost certain after sustaining 100 mA for 2 seconds.
(b) A person can only withstand less that 10 mili-amperes and still have control of his arm muscles. Beyond that, he no longer has control over his arms. That is the reason he cannot let go of the faulty tool he is holding (the hand may even tighten the grip on the electric tool), resulting in longer flow of shock current through the body thereby making the injuries more serious.
This situation when prolonged will lead to respiratory paralysis (the muscles that control breathing cannot move.)
That is part of the reason for the requirements to have install Earth Leakage Circuit Breakers (ELCB) for circuit supplying electrical tools. The ELCB can detect very small amount of leaked electrical current and trip that circuit within a fraction of a second thereby saving lives.
A severe shock can cause much more damage to the body than is visible. A person may suffer internal bleeding and destruction of tissues, nerves, and muscles.
Sometimes the hidden injuries caused by electrical shock result in a delayed death.
If a shock current is maintained long enough at a relatively high current, death is probably not avoidable.
But if somehow the contact area to the electrified object is broken fast enough and the victim’s heart has not yet been damaged, his normal heartbeat may return, even though this type of recovery is rare.

The severity of injuries depends on which part of the body does the shock current flow through

The most serious effect is when the current flow through the heart.
If a live wire accidentally touches the body by contact at the head, the nervous system will be severely damaged.
If during the accident the victim’s right hand touches the LIVE wire, while the left hand is holding the metal casing of the washing machine, the electrical current will flow through the chest. Then the lungs and heart will probably be injured.
Of course how severe will also depend of how many mili-amperes and how long the shock current flows.
If the current only flow through the arm portion, then the injuries can be as bad as the arm coming off while the victim still survive (not dead). There have been actual cases like these in high voltage accidents.
If the current does go through the chest, the person will almost surely be electrocuted.
A large number of serious electrical injuries involve current passing from the hands to the feet. Such a path involves both the heart and lungs.
This type of shock is often fatal.

A higher skin resistance will lower the shock current.

(a) Again the current is inversely proportional to the resistance. If the victim’s body is dry, then the shock current through his body will be lower. Then the injury will be less severe.
The resistance of a dry skin is can be 100,000 ohm or more. While that of a wet skin is only approximately 1,000 ohm.
At 600 volts, the dry skin resistance will only allow 6 mA at the most, while the wet skin can allow 600 mA to flow through the body.
Compare this to the list of injuries above and you can appreciate the extreme importance of dryness in the effort to avoid electrical shock.
Even at 240 volt, the wet skin will allow 240 mA to flow through the body, making very severe injuries and even death possible.
(b) Other wet skin, wet working conditions will have the effect because they can make the skin wet and reduce resistance. Likewise, a damaged or broken skin.
(c) The resistance will also be reduced in direct proportion of the cross-sectional area of the path current. This means that when the contact made to an electrified object with an applied force as opposed to touching it with the tip of the fingers, the contact area will be larger. Therefore, the resistance to the current flow will be lower and the shock current will be higher.

Very Low Voltage also can kill

(a) The severity of the injury can increase the longer the victim is exposed to the shock current. Because of that, even low voltages can be extremely dangerous because the degree of injury depends not only on the amount of current but also on the length of time the body is in contact with the circuit.
Some victims have stopped breathing when shocked with currents from voltages as low as 49 volts.
For example, a shock current of 100 mA applied for 3 seconds can cause injuries as severe as a current of 900 mA applied for a fraction of a second.
(b) The victim’s muscle structure also plays a factor. People with less muscle tissue are typically affected at lower current levels.

The higher the voltage, the more serious the injuries.

(a) A current flow is directly proportional to the voltage supplying the current. That is why the higher the voltage, the higher the shock current flowing through the victim’s body. Therefore, he injuries will be more severe.
(b) At high voltage (i.e. 600 volts), the shock current can be as high as 4 amps. That amount of shock current will damage the hearts and other internal organs. In addition, internal blood vessels may clot, and the nerves in the area where the skin touches the electrified object may be damaged.
(c) High voltages can also cause severe tissue burns. A strong shock at the limb can cause the limb to come off.

Higher voltage can cause further accidents, therefore additional non-electrical injuries.

(a) Sometimes high voltages can lead to additional injuries. High voltages cause violent muscular contractions. The victim may lose his balance and fall, which can cause further injury or even death if he falls into machinery that can crush him.
(b) Bones can be fractured as a result from extreme muscle contractions during the shock, or cause by falling from working height.

C. How electrical shocks happen

(a) General

A person gets an electric shock when an electrical current passes through the body. This happens when he comes into contact with live metal or live electrical conductors, which will cause the current to flow through our body.
A human body is not supposed to receive this sort of electrical current. Therefore, it is a shock and the body will suffer injuries. These injuries can be serious and can even be fatal.

(b) How the house wiring works

House electrical system in this country normally has three wires with one of them usually green color. The other two black may be black.
Another possible combination may be one black and the other red, yellow, or blue.
The green wires are connected to the earth through steel rods half an inch in diameter driven a few feet into the ground. The same ground wires at electrical substation or at power plants (i.e. diesel electric generators) are also connected to the earth mass the same way.
So the house green earth wire and the electrical plant’s earth wires are actually connected to each other via the earth mass. (Remember that earth mass contain water and minerals. Therefore, it is a good conductor of electricity, just like the electrolyte water inside the car battery).
So these green wires are at 0 volts.
One of the other two black wires, or the colored wires, in the house is at 240 volts and it is normally called the LIVE wire.
The last wire is the return path (also called the NEUTRAL wire) for the electrical current in normal operation. Remember that the current flow must return back to the substation (or the generator) for the electricity to work.

Visit this post, Home electrical wiring, symbols and checking, to know more about how a house wiring works.

(c) How electrical shocks happen

(i) When two wires are at two different voltages and they come into contact with each other, electric current will pass through them.
If they are not in contact, but your body connects the two wires by touching both of them at the same time, then electric current will pass through your body and you will get the electric shock.
(ii) If your body is in contact with the LIVE wire, while another part is touching a grounded object, you will also get an electric shock.
(Notes: A grounded object is:
1. Anything that in good contact with earth mass, like water pipes. Most authorities require that water pipes be grounded.
However, even if some pipes are not grounded, the pipes that are laid partly or wholely underground (i.e. the mater mains coming to the house) are actually in good contact with earth mass.
2. Or anything that is purposely connected to the earth mass, like the street lamp posts in front of the house.
Do not be fooled by the innocent-looking lamp posts, the compound lighting posts or the short bollard lighting posts at the park or by the street in front of the house. Many grown adults have actually been electrocuted and died just by leaning to the metal posts.
3. Or anything that is electrically connected to the house earth wires, like the metal conduit, the metal casing of the washing machines, etc.)
(iii) There is a much higher risk of electric shock if you are standing in a pool of water. For example when your kitchen floor is all wet with water from the overflow at the kitchen sink, or while you are cleaning your kitchen floor with water.
Worst still if the wet floor is at the living room because the a few power outlets there are normally installed at lower level (approximate 12 inches above floor level).
(iv) The chances of being electrocuted will be much higher under certain conditions like wet clothing, high humidity and perspiration.
(v) Electrical equipment that is not properly grounded also can cause electrical shock. A typical example of this scenario is when an electrical appliance cord has a 3-pin plug, but you attach a plug adapter to it so you can plug it into a 2-pin socket.
(vi) If you touch a person who is receiving an electrical shock, you will also get the shock. So, if you suspect that a person is down because of electric shock, do not rush to go and touch him.

D. How an ELCB operates

A (maybe) more technical name for the ELCB is Residual Current Device or RCD. This is because ELCB detects a current leaking to earth and uses this current to operate a tripping mechanism which then open the circuit breaker, stopping the incoming power supply. The current leaking to earth is a residual current so that gives the device its name.
The Figure shown below illustrates a typical schematic construction of an ELCB. A close observation of the schematic will reveal the principles of it operation.


On a healthy circuit the same current passes through the phase coil, the load and then return back through the neutral coil.
Both the phase and neutral coils are wound on a common transformer core such that they will produce opposing magnetic flux. With the same current passing both coils, their magnetic effect will then cancel out under a healthy circuit condition.
In a faulty circuit, the line current will be higher than the neutral currents, so the the line coils produce a stronger flux than the neutral coils. So the magnetic flux does not cancel out and there is a resultant or residual magnetic flux in the common transformer core.
Since this magnetic field is alternating and it crosses with the turns of the search coil (in the middle), a an electrical voltage develops in the search coil. This voltage then drives the current through the trip coil, which then trip the circuit breaker.
Observe that if a fault develop between the phase and neutral wires, the ELCB will not trip. This fault is seen by the devise just like a normal load with maybe a different wattage.
In order to safeguard the person touching an energized metal conductor (i.e. the load metal casing) during the leakage, the ELCB circuit is designed to detect a leakage current as low as 5 to 30 mA, and trip the circuit breaker in less than 0.1 second from the starting time of the leakage (the point of time the person touches the energized metalwork).
This will ensure that the shock current flow is removed or stopped before it reaches 50 mA, the lethal limit ( or so the experts say) for human.
A test switch is always provided on the ELCB so its operation can be regualrly tested easily. The test button works by bypasing the return coil. This simulates an out-of-balance condition so it trips the circuit breaker.
A test resistor is provided to limit the magnitude of the bypass current, and that is also used to check the sensitivity of the ELCB.
However it should be remembered (as explained in details in the following section) that the test switch only confirm the health of the ELCB unit, it does not check or confirm the condition of the shock protection system.

(a) What does an ELCB need in order to operate properly?

What does an ELCB need in order to work properly? I apologize for playing with words, but I am actually trying to emphasize a very important point. The question should be what does the shock protection need in order to work properly. The electricity users need to remember that electricity that comes into their houses carries with it dangers.
So the electrical equipment that is installed is not just to provide them the electricity, but also to protect the users from the accompanying dangers. There is a HUGE difference there.
So when we think about the electrical equipment and other electrical things in our home, think not just the electric uses that the equipment is supposed to provide, but also the dangers that the equipment is designed to protect us from.
That way we can train ourselves to be more alert to the hazards from electricity supply.
This point is particularly important in the case of ELCBs. An ELCB may be functioning properly and you can check this easily. While the electricity is on (i.e. not during the mains blackout) just open the electric panel cover, locate the ELCB unit and the TEST pushbutton on it. The test pushbutton will test whether the ELCB unit is working properly or not.
Now gently push the TEST pushbutton on it. If it trips (i.e. the ON/OFFswitch will snap and drop to the lower position. You can see the OFF label or symbol), then the ELCB is working properly.
Since the ELCB is working properly, then you are safe, right?
WRONG. The test facility provided on the home ELCB will only confirm the health of the ELCB unit, but that test does not confirm that the ELCB will trip when an electric shock hazard occurs. This misunderstanding has left many homes totally unprotected from shock risks.
This brings us to the second requirement for the proper operation of our home electrical shock protection system, which is the electrical grounding.

(b) A Functioning Electrical Grounding System

You can think of the ELCB as the brain for the shock protection, and the grounding as the backbone. Therefore, without a functional grounding there is totally no protection against electrical shocks in your house.
A brief on the grounding has been given at the earlier section of this article and I will not go into the technical details of the grounding today. That will be a title for another post in the near future, but a few major points must be stressed here to complete the lesson on Earth Leakage Circuit Breakers.
(a) An improperly grounded home electrical system is a serious hazard. In fact it is a serious hazard in any electrical system.
Unfortunately that is the most common violations of the electricity by laws. That is how prone people and companies are to overlook how important it is. Visit Home electrical earth installation for a more detailed discussion of house electrical grounding.
(b) All exposed metal parts and casing of the home wiring must be connected to the grounding system and it must be at 0 volt. Otherwise,they can be energized. How do we know that they are at zero volt? By testing, of course.
This is also another reminder for the DIY hobbyists who like this stuff. After you extend wiring, install additional electrical equipment (maybe like a small compressor in the garage), or whatever, ALWAYS test the new installation PROPERLY.
I know instruments that can really test this is not very cheap (notlike the multi-meters that you use to play with your electronic toys), but electricity is dangerous and the risks are loss of human lives, house and properties.
So either you buy one, borrow one, or get a qualified electrician to do it for you.
c) Ensure that all appliances and equipment that are plugged in also have their ground wires properly plugged in. Plug into safety first before you plug them into the power sockets. The metal casing of these things may be energized at some point of time.
If not properly grounded, the leaked voltage cannot be channeled into the ground, and therefore it cannot trip the ELCB. So anybody who happen to touch the casing will get the electric shock.
(d) The previous point brings us to the point of extension cords. They are one of the most highly abused electrical components in a home. Theyare very useful and very flexible. However extension cords are meant to be a temporary measure.
Do not use them as a permanent wiring. Due to its fragility the ground wires of these cords shouldn’t be relied on for safety, especially one of human lives.
So if you still insist onusing the extension cords, regularly check them for damage and broken connections.
(e) In many areas the metal water pipes are used as the grounding conductor to the earth mass.
If this is the system practiced in your place, make sure that all your pipe works are made of metals. Pay a particular attention to renovation works that might have been done to house or the piping (maybe by the previous owner).
If part of the piping have been upgraded or changed to non-metal piping then the grounding system now no longer works. Many house fires and electrocutions actually happened because of this type of errors.
If you are not sure about this at your house, and you are not good enough to check this yourself, then a qualified electrical contractor must becalled in to check it. A new grounding conductor that run to the whole house may need to be done just to be sure you have a proper grounding system in place.
(f) The last point I wish to emphasize on the grounding issue is about abuse, theft and vandalism to the copper parts of the electrical grounding. The abuse and vandalism part have always been there, but they were never a big issue.
However the issue of theft to electrical grounding (which also cover the lightning grounding) has become important in many places.
Maybe part of the reason is the rising cost of copper materials in thelast few years. Whatever the true causes are, the trend is clearly rising and this factor is very important to the integrity of the shock protection system (and the building's lightning protection system).
This is due to the fact that the system operates in silence and it is generally maintenance-free. Any missing part along the main ground path may not be noticed until major damages have been done or serious injuries have occured.
This brings us to the very reason why the electrical ground system must be regularly inspected. This is the only way to ensure it is working and that the electrical shock protection system is providing an optimum protection.

E. Other variations of ELCB

Other names are also used to call the ELCBs, the most common beingResidual Current Circuit Breakers (RCBs), Residual Current Devices(RCDs) and Residual Current Circuit Breakers with Overcurrent (RCBOs).
The difference in names is meant to show some difference in the design used in their manufacture. The purpose and operation of the parts are all the same. So do not be confused when they are the ones installed atyour house electrical panel.

F. How to test an ELCB

As described above, the ELCBs can usually be simply tested by a Test Pushbutton on the unit itself. It is recommended that the ELCB be tested once a month and after every thunderstorm to make sure it is still working properly.
However the electrical grounding system must also be in good working order for the shock protection system to work. In between the routine inspections that should be done by the qualified electrician, this grounding can be inspected regularly by the homeowner.
Just like other parts of the electrical installation, visually checking your home electrical is quite simple and it does not require much electrical skills.
If you feel you have found something that is not right with the electrical installation in your home, then a qualified electrical contractor can be called in to do a more detailed inspection and carry out the repair works if necessary.
Proactive attitudes towards this aspects of maintenance can effectively reduce the risk of electrical accidents at home and at workplace.
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