Here are the dangers of earth systems. Electrical power is supplied to a site through a two cored cable (active and neutral here). At the metering box all neutral leads connect to a common neutral link, i.e. leads coming back from various power and light circuits etc. Also connected to this neutral link is the earth wire leading to a bulk connection of all other earth wires. A further earth wire leads off to the water service and, in the case of more modern homes now, a separate earth stake driven into the ground.

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DANGERS OF EARTH SYSTEMS


 

Authored by Ian C. Purdie VK2TIP

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What are the dangers of earth systems?

This is an email I wrote to the QRP-L, the Low Power Amateur Radio Discussion group back on 24th October, 1999.

Date: Sun, 24 Oct 1999 08:16:25 +1000
From: "Ian C. Purdie VK2TIP"
To: Low Power Amateur Radio Discussion
Subject: ELECTRICAL EARTH WARNING

Guys and Gals,

I know this is quite basic but I have just concluded a discussion with a scout master re crystal sets (qrp!) and good earthing.

As most of you know I am a licensed Plumber here in Australia. In my time I have met many water services (copper or galvanized pipe) which were DEADLY LIVE.

Most of the electrical fatalities in NSW (my state) and presumably elsewhere are plumbers and electricians who were electrocuted by live earthing.

A typical scenario is this with M.E.N. systems (same in US and UK I believe):

Power is supplied to the site through a two cored cable (active and neutral here). At the metering box all neutral leads connect to a common neutral link, i.e. leads coming back from various power and light circuits etc. Also connected to this neutral link is the earth wire leading to a bulk connection of all other earth wires. A further earth wire leads off to the water service and, in the case of more modern homes now, a separate earth stake driven into the ground.

Taking the case where no earth stake exists, if the main neutral conductor coming into the house is interrupted (and often can be for a variety of reasons) then the only return path for electrical continuity is the earthing system, down through the water service, out into the street and back up through EVERYBODY'S water service / earth system.

Modern installations have (a) a separate earth stake in the ground AND (b) an insulating bush in the water service where it connects to the water main. Other areas / countries might well be different. Certainly millions of older installations world-wide are as described above.

How do I know a water service is live? Standard procedure (for those who follow rules and procedures - idiots don't) is to first connect, by way of proper earth clamp, an insulated earth wire of standard 4 mm size to the water service as it emerges from the water main. This cable is then run out to the meter box for connection to the neutral link.

Many, many times I have scraped this earth wire down the side of the meter box to be greeted by a shower of sparks. At this point both the law and common sense compel me to cease all work and contact the electrical authority who will arrive within half an hour. Often the cause is simply a broken neutral at the point of attachment to the house (if the active broke you would have no power). Other times it has taken teams from the electricity supply several days to locate the source.

Strangely, I have been abused by consumers for "creating trouble", especially after the electricity supply have put up a ladder and cut the active line for "immediate" safety reasons.

Sorry it was long winded, but it is a VERY REAL hazard. Many a plumber has died by cutting through old galvanized pipes. One was charged with manslaughter (rightly so) after leaving an inexperienced apprentice alone on site with instructions to "start removing the old gal pipe - I'll get the materials".

Just be aware!

73's

Ian Purdie
VK2TIP "I'll give you the TIP mate"
QRP-L member #1978.

REMEMBER: Only cat's have nine lives!

MAN KILLED WHILE FIXING BURST WATER PIPE

January 24, 2005

A Sydney Water employee was killed when he was electrocuted while fixing a broken water pipe in Sydney's west....

http://www.smh.com.au/news/National/Man-killed-while-fixing-burst-water-pipe/2005/01/23/1106415454178.html

FEEDBACK FROM A READER

Probably not meant in the way I took it, but.....

<snip>

"XYZ" wrote:

> "start removing the ol' gal pipe - I'll get the materials."

> You've got me laughing my ass off, all the way over here in the U.S.A!

My reply

Unfortunately that was one 17 year old kid who never got to realize his potential as a *star* footballer. His younger brother did later on.

20 years later, I still get as angry about it as I did the day it happened. His mum sent him to work to improve himself, not get killed by the stupidity and criminal negligence of his employer.

</snip>

FEEDBACK FROM ANOTHER READER WHO IS ALSO HIGHLY QUALIFIED ON THIS TOPIC

Most of my pages have a "rate-a-page" feature. This particular piece of feedback comes from rating this very page here.

<snip>

Below is your form's result. It was submitted on Wed Jan 30 06:27:39 2002. ---------------------------------------------------------------------------

page: http://www.electronics-tutorials.com/basics/earth-dangers.htm

rating: FANTASTIC

Comment:  Just wanted to let you know I stumbled across your page on Earth dangers, I will be recommending this page to others in an attempt to clarify this issue to others, I am an Electrical Inspector in Tasmania & have investigated many many shocks from water pipes where the fault is exactly as you described, I find it difficult to explain in non-technical terms to my customers what has caused the problem, you have managed to keep it simple so anyone can understand it - well done! (would you mind me printing this page & showing it to anyone I may think needs it?)

<snip>

My answer is obvious...

ERRATA

Australia does have and, has had for some considerable time, in common with many countries, devices called "Earth Leakage Circuit Breakers - ELCB" or "Residual Current Device - RCD". These are compulsory on all new installations and upgrades. However older buildings are *NOT* necessarily fitted with these devices.

RELATED LINKS - further reading

From my friend Glen E. Zook, K9STH

RF Grounding Primer - PDF File.

Lightning Primer

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