sparks
ELECTRICAL NEWS
june 2014
Cyril Berman of Superlume, writes:
I refer
to the front page article in the March issue of
Sparks Electrical News
regarding the new socket
outlet system for South Africa and, while I agree
that this country needed a new system for the
reasons raised by Gianfranco Campetti, I would
like to raise the following issues:
Why did SA choose to adopt this particular
design when no other countries have done so?
Noting that there are alternative systems widely
used throughout the world, such as the Swiss
Schuko outlets, which are equally safe and com-
monly used throughout the western world, and
the two- and three-pin systemused in Australia
(which has some of the highest safety standards
in the world) andmost of south-east Asia, includ-
ing China, why did we need to be unique?
We could have adopted either of the two sys-
tems above and there would have been no need
for extensive research, design, and development,
testing, and approvals, etc – and the economies
of scale would have made the transition quick,
easy, and cheap.
As it is, most foreign travellers coming to SA
have to buy adaptors to use their appliances
here, and the reverse is the case for SA travellers
going abroad. With this new SA system, nothing
will change, and adaptors will still be the order of
the day.
I further note that the new plugtops are non-
rewireable. This means that only appliances that
are wired originally with the new plugtops will be
suitable for use with this system, and, in order to
adapt existing appliances such as hairdryers, ket-
tles, toasters etc, one could only cut the cables,
remove the existing 16A plugtops and join them
to cables with the new plugtops already wired
on, thereby creating a dangerous situation that
SA’s new socket system questioned
did not exist before, and, furthermore, negate
any manufacturers guarantee, and transgress the
SABS wiring code for appliances.
I could raise many more reasons why this move
is, inmy opinion, a bad idea but I think there is
enough food for thought in the above.
Gianfranco Campetti replies:
I respond to Mr Berman’s points in the order that
he raised them in his letter:
In its original form, IEC60906 was intended to
be a‘worldwide plug and socket system’, which
was many years in the making. One of the princi-
ples that guided the IEC committee (SC23C) was
that it should not be compatible with any of the
current IEC systems. This objective was largely
met but with one exception: the‘Europlug’.
Back in the early 1990s, SABS thought it wise to
adopt this system for two reasons:
They felt that it was time tomove away from
the cumbersome and somewhat unsafe large
three-pin system and with the advent of a new
political landscape on the horizon, they believed
that a common Southern African plug and
socket system could‘fall in’with their plans for
harmonising the regional standards and it would
be more palatable to our 12 or so SADC neigh-
bours if this was an IEC standard rather than a
‘home grown’one.
The design was, of course, part and parcel of
IEC60906 and not developed by any SA entity.
The fact that no other country would adopt this
standard was not envisaged at that time. All ex-
cept Brazil, silently rejected it and after CENELEC
was unsuccessful in the European context,
about 15 years ago the EU set up a task team to
investigate the possibility of standardising plugs
and sockets in Europe. However, the task team
could not come to an agreement so the project
was shelved.
There was always the choice to
use any other system, but this did
not happen. I guess there was some
national pride at play but no reason
was recorded as to the pros and cons
of any of the systems mentioned by
Mr Berman. I do not agree that the
Australian or Swiss systems are as
safe as he makes themout to be, for
several reasons but this is altogether
another subject. The highest safety
standard he refers to is ultimately
IEC60884-1, which is also embedded
in the SA standards for plugs and
sockets.
Mr Berman's point about research
and design is not based on any
factual evidence, firstly SA had a
substantial manufacturing base for
wiring accessories, any transition to
another existing systemwould be
anything other than cheap, easy or quick and it
would have ultimately opened up the SAmarket
to imports at the expense of local manufacturers
and ultimately SA jobs.
The question of travel adaptors is a sore point
for any country, even in Europe where borders are
only a few kilometres apart, with few exceptions
each has its own national identity and unique
plug and socket system. With the new system, the
only difference for SA is that our fixed installations
will be compatible with the‘Europlug’, which, in
my opinion, is a positive step forward, since any
small appliances such as hairdryers, curling tongs,
gaming equipment and a myriad chargers, will
plug directly into a wall socket, without having to
resort to an adaptor.
AN earth continuity conductor serves a critical pur-
pose in an electrical system. It ensures that protec-
tion can operate and that equipment and people
are protected. If the earth continuity conductor is
broken or missing - how can you still ensure safety?
For electrical safety it is required to have earth
wires connected to the transformer star point
in any low voltage (eg 400 V/ 525 V) reticulation
system. Earth leakage or protection relays rely on a
healthy earth connection because they operate on
the current in the earth wire. With a broken earth
connection they are worthless. The earth connec-
tion can fail due to various causes, including cable
theft. When it fails it is tantamount to an electrocu-
tion waiting to happen.
Cable theft is often aimed at earth wires because
it is safer to cut them; in these cases there is also
the high cost of replacing the earth wires which, in
some installations, are 70mm
2
.
If a failure of the earth connection could be
detected and communicated as it happens, pro-
active measures would be taken to prevent further
damage and ensure safety.
Earth and cablemonitor
A recently developed earth and cable monitor
(ECM) could be the answer to earth connection fail-
ure. It uses an easy-to-install small clamp-on toroid
around the cable to be monitored.
It measures the wire resistance, relying on a re-
turn path. Inmost cases the other end of the earth
wire or cable has another earth connection which
leads back to the distribution point where the ECM
is located. This can be another earth wire or cable
armouring or even a specially installed pilot wire.
The toroid works partly in a current transformer
mode whereby the secondary winding and its
‘burden’resistor or load resistance is the earth wire
running through the toroid, having a connection
back to the distribution point. In the case of an
open-ended earthing cable a small pilot wire can
Monitor resistance of earth wire and improve safety
By E Häussermann, Mercutech; and J Warwick, Jojen Supplies
be run to the end
point in order to
close the loop.
The primary or
excitation winding
on the toroid is
subjected to a
near-constant cur-
rent of a frequency
well above 50Hz.
The wire to be
monitored and
running through
the toroid forms
the secondary
winding with a
load resistance.
The toroid also
has a signal wind-
ing in which a voltage is induced proportional to the
voltage on the load resistance which is the resistance
of the earth wire.
The primary winding is energised by short current
bursts (of a little longer than one 50Hz cycle) during
which time the voltage of the signal winding is
measured, after going through a band-pass filter.
With the operating frequency being well above
50Hz the clamp-on toroid can be kept small but the
measurement will also depend to a small degree on
the inductance of the earth wire circuit.
This could be a good thing because the alarm
signal is triggered by a change in the measure-
ment and therefore also by a change in the circuit
inductance.
For example, should an intelligent thief loop an
additional wire through the toroid before cutting
the earth wire, in an attempt to mask the effect of
the open circuit, the ECMwould in most cases still
detect a large enough change to raise an alarm and
display an earth resistance indication.
ECMproperties
For the standard clamp-on toroid
the change in resistance can be set
between 0,1– 5 Ohms. The ECM can be
set to send an SMS to several telephone
numbers in the case of an alarm.
While having the toroid around an earthwire, the
signal voltage is also filtered to see a 50 Hz earth
fault current.The ECMcan be set to raise an alarm
and/or send SMS’s and display an earth fault indica-
tionwhen the earth fault current exceeds a precon-
figured level. For the standard clamp-on toroid the
earth fault alarmcan be set in the range 1 – 20A.
The ECM has an RS485 port with an extensive
native protocol but can be set to communicate
in Modbus. In the SMS and the Modbus message
each of the eight inputs is identifiable. For best
performance each clamp-on toroid is connected
to one input but two clamp-on toroids can be
connected to an input with a reducedmeasure-
ment resolution.
The ECM is housed in a DIN-rail mountable
enclosure. While it will normally run on a 110 – 220V
supply (ac or dc) it can also run from a 12Vdc battery
to keep it running and raise alarms during a power
failure. It has a built-in charger to charge a 12V lead-
acid battery and keep it at full charge.
Conclusion
Cable thieves often target earth continuity con-
ductors because cutting and removing them is
perceived to be safe. However, a compromised earth
continuity conductor can lead to equipment dam-
age, injury or even death. This article has described
a proactive means of assisting inminimising risks in
plants.
Enquiries: Email
or jvwarwick@
gmail.com.
energy measurement and supply
21
At the moment there is only one manufacturer
that produces the SANS 164-2 plug-top and it
is rewireable. What we will be waiting for with
some anticipation, is the time when appliance
manufacturers will supply kettles, irons, toasters,
fridges and washingmachines with an integrally
moulded SANS 164-2 cord set, but I guess that
will be in a few years fromnow.
The changeover to this new systemwill not
mean that the SANS 164-1 (current system) will
be banned; it purely means the steady introduc-
tion of the compact SANS 164-2, which will be
installed side-by-side with SANS 164-1. Currently
many SAmanufacturers and importers offer
such a product, many have already been in-
stalled and used effectively inmany households
and offices.
Letter to the Editor
