Building Construction, Renovation & Maintenance

The Importance of Earthing in Electrical Circuits


Grounding or Earthing of Electrical Circuits

Probably the most important part of any electrical installation is that they are correctly earthed, or as some people say, grounded. If you get an electric shock electricity passes through your body to get to earth and this can injure or kill you. Electrical circuits are designed so that if there is a fault electricity can go to earth instead of passing through your body. The earth (or ground) connection in any electrical circuit is vitally important to keep you safe.


See the full Fixed Abode article "Earthing Delights" here


Electricity Naturally goes to Earth

We generate electricity by creating a voltage, a difference in power level between the positive and the negative wires in an electrical circuit. As we use electricity it will flow until this power difference comes into balance (for eaxample when a battery is flat all the electricity has flowed bringing the battery into balance - there is no power difference left).

The earth is huge and can abosrb all the power we can generate and so electricty will always flow to earth and be absorbed. This is why it is very enthusiastic about flowing through earth to earth if we get in the way.

We can use this to our advantage, to protect us. Through our electrical circuits we always provide a nearby connection to earth so that if there is a fault the power can flow harmlessy away.

We make sure that the steel body of a washing machine (or any other appliance) is always connected directly to earth. If there is a fault and the elctricity comes into contact with the body of the machine it can flow away to earth. If we touch the body of the machine we know we are safe.

In our electrical circuits we also have circuit breakers which will cut out and switch the power off if there is a sudden high flow of electricity through an electrical circuit. If there is a fault and electricity in our washing machine starts flowing into the steel body of the machine this can be very dangerous if we touch the machine but, if the body is connected to earth the electricity will flow away and the circuit breaker should switch the power off.

Earthing (or grounding) keeps you safe

Your protection for the electrical system in your house electrical circuits is the “earth” or “ground” connection. Unfortunately many people are not aware of whether their home is properly earthed.

The strict rules of electrical installation insist that appliances such as washing machines, toasters, computers and the like have their metal frameworks and steel cases earthed. Their power cables should have three wires:

  1. “live” - the brown wire (these used to be red).
  2. “neutral” - the blue wire (these used to be black)
  3. "earth" - the green and yellow striped wire (these used to be green.)

Note that these colours were changed when it was found that colour blind electricians were connecting the green earth wire to the live turning a washing machine into a death trap. In old houses you may find that the wires are still the older colours.

The live and neutral wires carry the power while the earth is the connection to earth.

In most house wiring, the lighting circuits have only the live and neutral wires (there is no earth) while plug sockets, ceiling fans and air conditioners have all three.

Earth wires come from each plug socket and connect back to your house distribution board, that's the one with the circuit breakers in it. Here the earth wires are connected together and in turn are, or should be, connected via a cable to a metal rod which is driven into the ground. The metal rod may be steel or ideally copper or copper coated and should be over a metre long.

Circuit Breakers (MCBs)

Circuit breakers have replaced the old fuses. Remember those? They were those little glass tubes with a fine wire inside or, before that, a piece of thin wire connected between two terminals in the fuse box. If something accidentally got connected to earth, such as you touching a live wire, the electrons would make a dash for earth causing a surge in current that, if it went through you, could burn or kill you. The surge in current would melt the fuse wire hence cutting off the power supply. Fuse wire was used for generations but was replaced many years ago by circuit breakers which are far more effective.

Earth Leakage Detectors

Circuit breakers when combined with earth leakage detectors are far more sensitive than the old fuses. They have a rating of usually 6, 10, or 16 amps, which is marked on the breaker just above the switch. This is the electrical current that the detector is rated to normally allow.

If the electrons break loose the breaker detects a surge in power and immediately switches off. They work extremely fast, faster than it take to say “Flipping Heck that hurts!” faster even than an Aussie offered a free beer at a footy match. This is because electrons move pretty fast when they get excited, you'd have trouble catching one I'll tell you.

The result is that you live to tell the tale and your house doesn't burn down.

There is, however, one unfortunate snag. Earth leakage detectors don't work properly if the distribution board is not earthed. In many places you will find that many houses are not properly earthed.

I recently inspected some professionally built villas. The electrical systems look well installed using good materials but when I looked in the distribution box the earth cables were hanging loose, none of them had been connected and an earth cable had not been installed.

Make sure electrical fittings are earthed

You will also find that if you use low cost plug sockets, plug boards or plugs themselves they may not have earth connections in them. You should check this. Have a look at all your plugs, and particularly plug boards, they should have two pins or holes for the live and neutral power and then two metal strips down the outside which engage with metal strips in the plug or socket. If either the plug or the socket don't have earthing connections then they are not earthed. This is alright on an appliance such as a hair dryer with a plastic body but things like washing machines and computers should always have an earth.

Lightning conductors need a good earth

Lightning conductors also need to be earthed properly. Most houses don't have such things but if you have a house in a high position you may consider one. A copper spike on the roof connected by a substantial copper ribbon to a heavy duty earth rod. If lightning strikes the copper provides a safe path to earth protecting your building from what could be substantial damage.

A friend recently reported climbing onto his roof and finding that his internet dish had been bolted to his lightning conductor. To make matters worse the top of the dish was installed higher than the conductor. He rang the well known company that provide the internet service and they told him they usually bolt the dish to the lightning conductor.

Not a good idea.

At the highest point of your house you have a metal dish connected to your computer which in turn is connected to earth. In the highly unlikely event of a lightning striking your house you may have twenty million billion trillion electrons all heading home to mum through your computer and Windows doesn't come with a lightning conducting programme.

You could go into the internet and do a search for a driver for your lightning conductor but I suspect you may have trouble finding one.

A better idea is to avoid using “Lightning Internet Services” even if they do promise fast download speeds.

So to summarise, check that your house has an earth connection, that the plug sockets are all properly earthed and that your computer is not connected to Benjamin Franklin’s kite.



Copyright © Phil Wilson September 2007
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