Earth Leakage Faults

Natures way of saying water and electricity don’t mix!
Well to be more precise it was this sucker that kept tripping our shore line RCD.

travelkettle

Only what actually is “earth leakage”.
Wiki says:-
An earth leakage circuit breaker (ELCB) is a safety device used in electrical installations with high earth impedance to prevent shock. It detects small stray voltages on the metal enclosures of electrical equipment, and interrupts the circuit if a dangerous voltage is detected.

Which probably means not a lot to many.
So here is my (hopefully) KISS explanation.

CAUTION, Dangerous advice.
Check with a professional to ensure what I’m saying is right.
Electricity is NOT something to take lightly!

Anyway this was written for SWMBO in mind (she likes pictures).

Nearly all electrical supplies going into something have a Live, Neutral, and a ground or Earth wire. (There is something else called a double insulated device BUT that’s not like a kettle so I’ll ignore that for now).

picture 1

Electrical Current goes in on the live wire, “does it’s job”, and returns along the Neutral Wire. In – Out, no fuss. The Earth wire’s job is to BOND any metal chassis to an electrical zero place i.e. EARTH. Nothing with electricity coursing through it should ever touch the chassis and you are safe to do so.

Until there is a fault.
The sort of fault I’m talking about is when something internal carrying the electrical current TOUCHES the casing. WHAM! The Earth wire provides a perfect short to (funny enough) the Earth and the fuse gives in with a pop!

picture 2

Once that fuse has gone pop, no more electricity can leave the plug along the wire, everything is safe, there is no hazard!

Only it doesn’t work out like that some of the time and the internal fault only trickles a bit of the electrical current into the casing. (Water or condensation for instance).

Now it doesn’t matter about the Earth line being good or not (aka busted), the casing is loaded with electricity just waiting for someone to pick it up.
PHUT, you die as you provide an additional path for the electricity to earth, and the fuse hasn’t even hiccuped although it may be running hot..

picture 3

It doesn’t need a lot of electrical current to wreak your day either.
To interrupt the heart rhythm it only takes an electric current as low as 30 mA  aka 30/1000th of an ampere (the unit of electrical current), and with Direct current DC (think batteries for supplying this), 300 to 500 mA aka 3/10th to 1/2 an ampere across the heart.

In the UK (as standard) we only fit two sorts of fuses to our appliances.
3 amps and 13 amps. (around 700 to 3000 watts).
Or, just under one bar of an electric fire to a 3 bar electric fire.
Whoops, you die and the fuses are still intact.
Sobering thought isn’t it?

Enter the residual current device (RCD). An intelligent life saver!

picture 4

This sucker measures what is going in against what is coming out.
Current going in, and what flows back down the Neutral or return wire.
NOTHING TO DO WITH THE EARTH WIRE!
Only if it finds a discrepancy (some current is leaking away to Earth), it opens a safety (trip like) switch! Thus an RCD is designed to protect against the risks of electrocution and fire caused by earth faults.

See, a happy smiley person as the RCD has cut the power before anything can hurt him!
What was going in was not matched by what was coming out as some was being “shunted” along the Earth wire.

picture 5

RCD’s come in a few “trip current” sizes.
The recommended tripping current for shock protection is a maximum of 30 mA and this is the current recommended in the UK Wiring Regulations.

A tripping level of 100 mA will a give degree of shock protection if it is not possible to use a 30 mA device. This sometimes occurs when you use certain types of electrical equipment in industrial premises.

A 300 mA device should never be recommended for shock protection and is only intended for equipment and fire protection.

A 10 mA RCD should be used for 110 volt supplies because levels of less than 30 mA could flow through a body in the event of a fault. A 10 mA device is sometimes recommended when the likelihood of shock is increased such as when people are working with live equipment.

So how do I check if I’ve got such a device fitted?
Look at your fuse board and have a look to see if there is a device with a push button marked ‘T’ or ‘Test’.
This ‘test’ button is part of an RCD.
If an RCD is fitted, there should also be a label on or near the consumer unit stating ‘test quarterly’.
How do you test it? Press the TEST button and all power should turn off.
To reset it, simply push the now tripped switch back up to its original position.
Only be kind to it and turn off the large consumers of power before you do this.
Testing it with a maximum load can over stress it.

picture 6

So what do I do if a RCD trips?
What were you doing at the time?
If you had just plugged something in, it MAY be faulty.
Unplug it and reset the RCD. If it resets you’ve got a faulty appliance.

IF the RCD just decided to trip to upset your day (it happens, electrical things can smell fear just as computers do), just reset it. BUT TWO trips in a short time is an indicator something is going wrong!
Only if it TRIPS again or WON’T reset at all, something is VERY, VERY WRONG.

Now it’s a process of elimination.
Turn everything off and unplug what you can.
Reset the trip.
If it resets, gently plug things in again until the item that is faulty trips the RCD switch off.
Simple eh? A process of elimination.
If however it won’t reset, call an electrician. It could be one of two things.
You’ve got a serious wiring fault OR the RCD itself has given in.
Either way, GET PROFESSIONAL HELP!

Any questions SWMBO ??

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2 Responses to Earth Leakage Faults

  1. SWMBO understands it better than she did…….. smiley man indicates he’s going to get his dinner!

  2. Rifleman III says:

    If capacitor (f), does not fit into circuit (j), the resistor (m), will result in circuit (b) failure, and you will get toasted, looking like Beetljuice: http://www.youtube.com/watch?v=CiLKrDWgGYs

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