Inside your earth leakage
Bruce Brook
 

When was the last time you got badly shocked by an electrical supply? It was probably a long time ago, and if not, the shock was for less than a second anyway.

The reason for this is the mandatory installation of an earth leakage unit in your home. These miracle devices have saved thousands of lives in our country alone and monitor the condition of your electrical circuitry 24 hours a day, seven days a week.

At times they can be downright irritating and leave your home in darkness when they detect a fault and trip, and sometimes they become faulty and have to be replaced at high cost on a weekend or public holiday.

Most of the time they fulfil their task tirelessly and protect us, the general public, from the hazards of electrical shock.

For obvious reasons, never bypass the earth leakage. Earth leakage detectors can be pricey, but nowhere near the cost of human life.

How they work

To understand the concept behind the earth leakage unit we can look at a three pin plug.

There are three electrical wires entering the plug and sometimes only two but in order for anything electrical to work you need it to be connected to the live and the neutral supply. If you disconnect the neutral, the device will not work even though there is still power in the live wire.

This is because we have an open circuit or a break in the circuit and the current cannot flow back down the neutral line.

So we need two wires to get the current flowing and it is a natural deduction to state that the amount of current flowing down the live wire has to be exactly the same amount of current flowing back down the neutral wire. It seems obvious and in a round electrical circuit, it is, but introduce a human being into the equation and you've got problems.

You see, we humans, aside from our physical and psychological defects, have other problems — we conduct electricity and we're not very good at it but the electrical resistance in our body is low enough to allow normal house current to flow through it.

Now let's get back to our circuit. We have current flowing up the live wire, through the electrical appliance, and back down the neutral wire.

Let's assume that someone has damaged the cable connected to this appliance and is trying to repair it without unplugging the appliance. He touches the live wire and gets a shock. Why? Because current is leaking through his body down to the floor that he is standing on (what we call earth). Now, does the current that flows up the live wire still have the same value as the current flowing down the neutral wire? The answer is no because some of the current has 'leaked' out of the circuit, through the person, down to earth. Hence the term 'earth leakage'.

Think of your electrical circuit as being a hosepipe filled with water, and someone puncturing it, causing a leak. The volume of water flowing into the pipe is not the same as flowing out the other end because of the leak. A simple analogy but it helps us to understand what is going on.

Now, if we could have a device that can accurately measure the current flowing down the live wire, and continuously compare it to the current flowing back up to the neutral, we could check if there is a difference between the two, and the device could switch off the power. This would prevent our guy, who is still being shocked while repairing the cable, from dying.

The good news is that this device already exists and it is called an earth leakage detector, commonly known as an earth leakage and this is exactly how it works. If the difference in current flowing between the live and neutral wire exceeds more than 20 milliamps to 60 milliamps (depending on the sensitivity of the unit) the detector trips the power, preventing further electrical shock.

If you walk to your DB (distribution) board you will find it situated on the left next to the mains and it can be identified by a test button. There will also be a sensitivity value printed on the label (20mA to 60mA). But why, you ask, does my earth leakage trip and yet no one has been shocked? The answer is simple. The device tests the roundness of all electrical circuits in your home and there can be a fault in one of there circuits causing current to leak to earth without a human being involved!

For instance, your geyser could have a faulty element because of a bad insulation between the element and the outer tube. If the poor insulation allows a current to flow more than the sensitivity range of your earth leakage unit, the earth leakage will trip.

Tripping problems

If your earth leakage has tripped and you can't get it on again, you should: Go to the DB board and pull down all the circuit breakers. Now try to switch on the earth leakage. If it goes up start by switching on the circuit breakers, one at a time from left to right.

Wait a few seconds between each breaker to see if the earth leakage trips. The breaker that causes the earth leakage to trip will be the one with the faulty circuit. Get the rest of the breakers up and check which one it is. Common faults are:

• Geyser — as mentioned it is probably a faulty element.
• Stove — a faulty element, you may be able to isolate which plate causes it to trip and refrain from using it until you've had it repaired.
• Lights — this is very rare but sometimes occurs if you have a water leak in your roof. Get the leak fixed and use table lamps for lighting until things dry up and you can switch on the breaker. If you can't find a roof leak, contact an electrician.
• Plugs — this is the most common one. Disconnect all appliances, computers, garage and domestic room power and try again. If it stays up start plugging things in one by one until the earth leakage trips again.

This will tell you which appliance is faulty. If not, make sure that you have removed every plug — some are hidden in bedroom and kitchen cupboards. If you are sure that nothing is plugged in and the problem still persists, call in an electrician.

If you have switched off everything and the earth leakage still won't stay up, feel if it is warm. Wait a few minutes for it to cool before trying again. If it has been tripping often for no good reason it may be faulty and need replacing. Call in an electrician as soon as possible.

 Back Home