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Your House
Water Pipes
could
ELECTROCUTE You!
Do you have RCDs (so-called “safety switches”) fitted in your home’s
switchboard? Do you think that eliminates the chance of electrocution?
Well that isn’t the case because the copper water pipes in your home
could easily become live and dangerous! That is why some people have
been electrocuted in the shower . . .
U
ndoubtedly modern Australian homes have safe wiring
when they are first built. They
would not be “signed off” as such
before occupancy certificates were
issued if they weren’t.
But corrosion and wiring or plumbing modifications over the years can
easily produce a dangerous situation
which could cause a fatal electric
shock.
It is partly because of the M.E.N.
Electrical Wiring System used in
Australian homes. M.E.N. stands for
“Multiple Earth Neutral” and is the
system used for wiring the majority
of domestic electrical installations in
Australia.
As specified in the SAA Wiring
Rules (AS 3000-2007), the mains Neutral wire is connected to Earth at the
user’s switchboard.
In most houses this means that the
230VAC mains supply is connected
from the power pole in the street via
two cables, Active and Neutral, with
the Neutral wire typically connected
14 Silicon Chip
to Earth via the consumer’s water pipe
(or a separate Earth stake).
The Earth connection point on the
water pipe is usually just at the point
where the pipe enters your house.
This is important because you need
to examine it occasionally to make
sure that the connection is sound. As
we will show, that Earth connection is
vital to the safety of everyone in your
household. Typically, the Active and
Neutral wires from the power pole to
your house have a capacity of 70 or
100 amps. This means that the maximum electricity consumption (volts
multiplied by amps) for the household
is nominally 16kW (kilowatts) in the
case of 70A mains and 23kW in the
case of 100A mains.
Happily, most homes normally use
only a small fraction of their installed
wiring capacity, although there would
be times during winter evenings when
it could be easily approached in large
By LEO SIMPSON
households when air-conditioning, a
microwave oven, a stove and perhaps
one or two other cooking or heating
appliances are in use.
Why M.E.N?
“Multiple Earth Neutral” is a system
which offers improved safety and
lower losses in energy transmission.
Let’s see why.
In a normal single-phase 230VAC
wiring system (which is what most
households have), the nominal voltage
of the Neutral wire coming into your
switchboard is the same as earth, ie,
zero volts. But in practice, the voltage
is a little higher because all the current
from your house and your neighbours’
homes inevitably causes a voltage drop
in the Neutral cable between your
power pole and the nearest substation
or pole transformer.
This is because the resistance of the
Neutral cable is not zero and the large
currents passing through it inevitably
means that there is some voltage present on the Neutral line. This voltage
siliconchip.com.au
CIRCUIT
BREAKERS
RCD
WATT-HOUR
METER
80A
GPOs
OVEN
COOKTOP
AIR CON
ETC
RCD
CIRCUIT BREAKER
SERVICE
FUSE
LIGHTS
RCD
ACTIVE
WATT-HOUR
METER
RIPPLE TONE
CONTROL
(OR TIME SWITCH)
20A
CIRCUIT BREAKER
OFF-PEAK
HOT WATER
HEATER
FROM
STREET
NEUTRAL
NEUTRAL
LINK
This simplified diagram depicts the electrical switchboard of a typical
home using the “Multiple Earth Neutral” (M.E.N.) system. It does not
take into account the fact that more Neutral connections are required
than shown here (eg, to the RCDs and off-peak hot water tone control),
nor the fact that some appliances (stoves, cooktops and air conditioners,
for example) may be supplied from a circuit not protected by an RCD to
minimise nuisance tripping. The Service Fuse may be mounted on the
switchboard or it may be mounted on the barge board, etc, where the
wires from the street are attached.
is a loss in the energy transmission
system and is part of the reason why,
when energy demands are heavy,
the mains voltage available at your
switchboard is lower than it should
be; the Multiple Earth Neutral system
mitigates this to some extent.
Because the Neutral wire is connected to Earth in your switchboard,
there are actually two return paths for
the current passing through the appliances in your home.
Some of the current passes back
along the Neutral line, back out to the
power pole and thence via the power
lines back to your local substation, pole
transformer or whatever. The rest of the
current passes back via the earth wire
to the water pipe and then via good
old Terra Firma itself to the substation.
(Editor’s note: we have simplified
matters here by ignoring the inhersiliconchip.com.au
ent current balance of three-phase
power energy distribution systems.
For a brief explanation, see the panel
headed, “Current flow, three-phase
and all that”.)
If you are not familiar with the
mains distribution system this may all
sound like heresy but it is true. Have a
look at Fig.1 which depicts the simplified 230VAC mains wiring of a typical
modern household installation with
electric (off-peak) hot water heating.
This diagram shows the Active and
Neutral connections to the switchboard. The Active wire is connected
via two watt-hour meters, one feeding
the off-peak hot water service and the
other feeding the rest of the power
circuits in the household.
Following each watt-hour meter is a
circuit breaker which is typically rated
at around 80A (amps) and is connected
NEUTRAL
WIRES
EARTH
WIRES
FROM
GPOs
ETC
BUILDING EARTH
TO WATER PIPE
OR EARTH STAKE
via the RCDs (residual current devices)
which protect the power and lighting
circuits in the household. From there,
a number of circuit breakers feed the
individual circuits for the stove, oven
and GPOs.
By the way, in the Australian wiring standards (AS/NZS3000), power
points are referred to as GPOs which
stands for General Purpose Outlet.
All the Neutral return wires from
the household power and lighting
circuits are connected together at the
Neutral Link. This also connects to all
the earth wires from the power and
lighting circuits as well as the main
earth wire, which in turn connects to
the water pipe or in some cases to a
mains earth stake driven well into the
ground. It also connects to the Neutral
wire which comes directly from the
power pole.
August 2014 15
they otherwise would if the M.E.N.
system was not used. They also
experience less voltage flash-overs
from Neutral to Earth during thunderstorms in appliances which are
permanently connected.
A common example of this used
to occur in stove heating elements.
Even though the stove or oven might
have been turned off, a lightning
strike on a power line would cause
many stove elements to break down
to chassis.
With the M.E.N. system this is
much less of a problem.
Wherein lie the problems?
On this one pole are the Neutral and three Active phase wires (on the crossbar
at top) with the Neutral having the most connections; below that are two cable
TV/broadband services and telephone lines. Normally, the phone and at least
one cable TV line (Telstra) would be underground but this pole sits in a hole
drilled into solid rock. Note that we haven’t mentioned an Earth wire – under
the M.E.N. system, the Earth connections are virtually always made at the
consumer’s premises.
(We are ignoring the separate Neutral links which are used for each
RCD. These additional links are used
because the RCDs monitor the balance
between the Active and Neutral currents in their respective circuits).
So it is a fairly straightforward circuit and it would be natural to assume
that all the current which comes in
via the Active feed wire goes out via
the Neutral wire. In other words, the
current in the Active wire is equal to
the current in Neutral wire.
It ain’t necessarily so!
It is possible that as much as half (or
even more) of the return current goes via
the Earth wire and the remainder goes
via the Neutral back to the power pole.
To take a particular example, if you
were using a 2400-watt radiator which
draws 10 amps from the Active line,
6 amps might go via the Earth wire to
the water pipe and the remainder, 4
amps, would go via the Neutral return.
The simple explanation for this is
that the resistance of the Neutral cable
back to the substation or pole transformer is slightly higher than the very
low resistance via the earth path to the
same point. Ergo, some current goes
via Earth and some goes via Neutral.
It can’t all go via Neutral.
Having come to terms with this
previously unconsidered fact, what
does it mean? It means that the supply
authorities are able to obtain lower
supply losses in the return path than
Corrosion is the first problem.
Since many small appliances these
days use thyristor power controls
there is inevitably a DC current imposed on the mains supply. Some of
this current will flow via the connection between the Earth wire and the
water pipe. And the very presence of
DC will accelerate corrosion which
naturally occurs when dissimilar
metals are used, as they normally are.
Ultimately, corrosion of the connection between the Earth wire and
the water pipe will mean that the
connection will be broken. Or if it
does not become physically opencircuit, its resistance may be so high
as to be useless.
OK, so that means that if you
have lost the Earth connection and
an appliance such as your washing
machine breaks down from Active to
chassis, the chassis could be lethal.
That is bad enough but consider another possibility which is even more
likely and happens quite frequently.
If corrosion has occurred in the
connection between your main Earth
wire and the water pipe, is it not
just as likely that corrosion has progressed in the Neutral connections
between your house and the power
pole? Of course it is. What that means
Current flow, 3-phase and all that
We have made a number of simplifications in the
writing of this article. The first is that we have said that
current flows from Active to Neutral or from Active to
Earth, as the case may be. In fact, since we are talking
about 50Hz alternating current, the current changes its
direction 100 times a second.
It is convenient to think of current flowing from the
Active line though, because in the words of an electrician
we know, “It’s the Active line that gets ya. It’s the one
with the juice!”
16 Silicon Chip
The second simplification involves the concept of
Neutral current flowing back to the substation, pole
transformer or whatever. This ignores the fact that
domestic mains power distribution from the power
pole has three phases, each of 230VAC (with 120° phase
difference between each). In an ideal system, the currents
should be balanced so that there is no current flowing
in the Neutral line.
Domestic systems are typically single-phase, so
appreciable current does flow in the Neutral return.
siliconchip.com.au
is that the Neutral return could now
have an appreciable resistance and
could easily be around 5 ohms or more.
If that is the case, all of the return
current will go via the Earth and water
pipe. But what if the Earth connection
has broken? What that means is that if
you now have an appliance drawing
5 amps, the voltage impressed across
the Neutral return path from the
switchboard to the power pole will
be 25 volts AC.
Hmm. So the Neutral link will be
floating at 25 volts AC above Earth.
And all the earths from the various
points in the house are connected to
the Neutral link. So every appliance
plugged in will have its chassis floating at 25 volts AC above earth. In time,
this could get much worse.
So your fridge, washing machine,
toaster and microwave oven could
all be sitting there silently with their
metal cabinets at a substantial voltage
above earth. Touch one of those and
a properly earthed metal object, such
as your kitchen sink, at the same time,
and it could be curtains!
It does happen.
Of course, another corrosion scenario is also possible and it also does
happen. What if corrosion in the
Neutral connection has resulted in
high resistance or an open-circuit?
In that case, all the current will flow
in the Earth. All your appliances will
continue to work and will be perfectly
safe. Your RCDs will continue to monitor for any imbalance between Active
& Neutral currents into your electrical
system. No problem.
But all that current is now flowing
in your Earth connection. And in
many homes, that Earth connection is
via your water pipes. If you have an
AC clamp meter, your can check this
yourself. Just wrap the clamp around
the water pipe just where it goes via
your water meter, as you can see in
one of the pictures in this article. You
can see the clamp meter is reading a
substantial AC current!
Does this ring alarm bells?
Well, it should. That water meter is
a potential death trap!
If a plumber needs to disconnect the
water meter, he may be interrupting a
circuit in which a substantial mains
current is flowing. If the water meter
is removed, there could be a very high
voltage between the two ends of the
pipe and there is a danger that the
poor unsuspecting plumber could be
electrocuted.
Fortunately most plumbers know
about this hazard and before removing
a water meter, their standard practice
is to bridge around the water meter
with a set of car battery jumper leads,
before it is removed.
Mind you, plumbers have been
known to create a hazard further
downstream from the water meter by
replacing a length of copper pipe with
If this isn’t enough to scare you, perhaps it should be. The load (inside the house) was a nominal 2400W heater, so the total
current drawn is just shy of 10A. That’s what we’d expect to see on the main Neutral line (the left photo). But it’s only 4.32A
– the other 5.06A is actually flowing through the (green/yellow) Earth wire in the photo at right. If your Earth connection is
in any way faulty . . .
siliconchip.com.au
August 2014 17
plastic, thereby breaking the Earth connection and creating a shock hazard.
So what might be the likely signs
that you have a hazardous condition
in your wiring or water pipes? Perhaps
the most dangerous is where people
receive an electric shock or tingle from
the water taps over the kitchen sink,
or worse, while in the shower. If this
ever happens to you or one of your acquaintances, you should immediately
contact your electricity supply retailer.
They should have an inspector out to
check the situation in very short order.
And often they will find in a defect in
the Neutral wiring back to the supply
in your street.
But you don’t have to wait for this
dangerous situation to develop. You
can make a few checks yourself.
Switch on and place the clamp meter
over the Earth wire to your water pipe
or Earth stake. Some AC current is
bound to flow and it could be 6 amps
or more.
So what if you measure a current
of close to 10 amps? That’s when the
alarm bells should be ringing because
that means that you have no Neutral
current and no Neutral connection out
to the wires in your street. That means
that your water pipes and taps could
become live and lethal, as outlined
above.
If the Earth current is more than say,
5 amps, you have cause for concern. In
that case, you should contact your local electricity authority and have them
check out your Neutral connection.
Don’t do this test during or just after
wet weather. When the ground is saturated, more current will tend to flow
What you should do
Do you know where your main Earth
point is?
Take a walk around your house.
Where does the water pipe enter the
house? That is probably the point
where you will find the Earth wire
connected via a screw clamp.
If you can’t find it, have a look at
your switchboard. There may be a
note (in white paint) saying where
the Earth is.
In some areas where the water service is run in plastic pipe, or the copper pipes do not make intimate contact
with the ground (eg, when the pipes
are run above ground or on rock) the
authorities specify that the Earth connection is made to a long copper-clad
steel spike or rod driven at least 1.2
metres into the ground, Alternatively,
the Earth connection may be made to
a strip electrode at least three metres
in length and buried at least 45cm
underground.
When you find the connection, inspect it carefully to see that it is sound
and not corroded. If the connection
is badly corroded you should have it
attended to by a licensed electrician.
Use an AC clamp meter
But there is a better way to check
the integrity of your Earth connection
and that is to use an AC clamp meter.
First, you need to have a substantial
AC current flowing in your home’s
wiring and the best way to ensure that
is switch on an electric radiator, preferably one rated at 2400 watts because
that means that it will pull a current
of close to 10 amps.
18 Silicon Chip
This reading of 5.39A in the water pipe between the house and the water meter is
not at all atypical – it can often be more. But just imagine if a plumber (or anyone
else) disconnected the water meter or severed the pipe – it could be very easily be
lethal!
siliconchip.com.au
via earth than via the Neutral path.
Warning
Many people will not be qualified
or feel confident to make any measurements as described in this article.
If they suspect that their electrical
wiring is unsafe, they should contact
a licensed electrician or the electricity
supply authorities.
A number of serious questions remain to be answered. Do the electricity
supply authorities have any program
for periodic checking of customers’
Active, Neutral and Earth connections?
Or does the first indication come from
the customer, complaining that they
“got a tingle from that appliance”?
And are plumbers and employees of
the various Water Boards instructed to
take any special electrical safety measures when disconnecting a customer’s
water supply?
The simplified diagram of a typical switchboard on page 15 does not show any
details of all the Neutral connections which are necessary for the RCDs. This
photo shows typical RCD Neutral link connections.
Currents can flow even when the power is turned off!
As part of the preparation for this
article, I used a Digitech AC clamp
meter (Jaycar Cat QM-1561) to
measure Neutral and Earth Currents
at my switchboard.
I also measured the current flowing
via the water meter and I noticed that
much greater currents were flowing in
the water meter than could possibly
be attributed to my home consumption when the load was only standby
power from cordless phones and other
appliances.
So while the total consumption was
much less than 100W, the current in
the Earth was as much as 4A, or more!
I turned off the power at the main
circuit breaker and the large Earth
current was still there. Checking the
Neutral, I found that virtually the same
current was flowing in the Neutral.
How could this be? This was quite
independent of anything in my home.
I also measured the current flowing in
my next door neighbour’s water meter
and found that it also had substantial
current flowing, even though no-one
was home.
At this point I contacted Energy
Australia, my electricity retailer, and
they sent an electrician out within
hours. He first confirmed that about
55% of the load current was flowing in
the Earth and the rest via the Neutral.
But he used a much larger load current. Instead of simply switching on a
siliconchip.com.au
2400W radiator as I had, he over-rode
water meter can lead to burnt O-rings,
the Zellweger ripple tone control switch
leading to a complaint of tainted water
to allow the hot-water tank elements to
from consumers.
SC
cut in. This gave a total load current
of 31A.
He also confirmed that current flows
in the Neutral and Earth when the mains
supply fuse is disconnected. He said
that this is not uncommon and does
not necessarily indicate a fault in the
household system.
He then proceeded to do a system
integrity check with a Fluke 1654B Multifunction Tester and came up with figures
of about 0.35 ohms for the Neutral path
and 0.3 ohms for the Earth which he then
pronounced to be quite safe. The test
procedure is according to Australian
Standard AS/NZS3017.
(An alternative instrument for
this testing would be the Metrel
Instaltest 3017 from Emona Instruments [www.emona.com.au]
which was reviewed in the September 2008 issue of SILICON CHIP).
He was very thorough during
the testing, wearing three pairs of
gloves, rubber boots and protective
goggles which is a mandated procedure.
He also confirmed that anyone
finding high currents flowing in the
The Metrel Instalset AS3017 Test Set from
water meter should contact their Emona Instruments. It’s not cheap (in both
electricity retailer. Apparently they senses of the word!) but if you’re involved
get most calls of this nature from in installation or checking of electrical
plumbers or from Sydney Water.
installations, it makes short work of what
Interestingly, high currents in the could otherwise be laborious tests.
August 2014 19
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