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E L E CT R I C AL CONNE CT I ON
S P R I NG 2 01 5
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when isolating the supply is more
dangerous than the short-circuit;
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where consumer mains are installed in
accordance with Clause 3.9.7.1; and,
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between generators, transformers,
rectifiers or batteries and their associated
switchboard.
However, strict conditions are detailed.
The installation of current-limiting fuses
is one way of controlling the available fault
energy at a particular location. Downstream
protection may then be rated lower than
normally allowed (Clause 2.5.4.5 [a]).
CO-ORDINATION
Co-ordination of protective devices is
important to ensure safety and minimise
the extent of the outage.
We don’t want to isolate parts of the
installation that are not involved in the
fault (see Clause 2.5.7.1 on the reliability
of supply). To this end, the Wiring Rules
provides guidance on co-ordination
(Clause 2.5.7.2).
RESIDUAL CURRENT PROTECTION
Residual current device (RCD) protection
seeks to prevent earth leakages posing a
substantial risk of electric shock.
Such protection came to prominence
in NSW in the 1970s with earth leakage
circuit breakers (ELCBs) being installed
on an installation-wide basis. This was
problematic and we have seen RCDs
become cheaper, more reliable, generally
installed on separate circuits, and with
increased focus and usage as specified by
the Wiring Rules.
I have written extensively on RCDs
previously and will briefly sum up the
requirements of the Wiring Rules.
The Wiring Rules have been adapted
to prevent nuisance tripping by including
Clause 2.6.2.1 and 2.6.2.4, which state:
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leakage currents are recommended to
be less than one-third the RCD tripping
current;
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the number of socket outlets and
the nature of the equipment likely
to be connected to the RCD is to be
considered;
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there will be no more than three final
sub-circuits per RCD; and
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if there are more than one final sub-
circuit, a minimum of two RCDs must
be installed.
Lighting circuits are to be distributed
across circuits where there are more than
one RCD and more than one lighting circuit.
A Type S, 100-300mA RCD is
recommended as a main switch in
domestic installations to help prevent
electrical fires caused by current leakage
across insulation (Clause 2.6.2.3). If it is good
enough for the Wiring Rules to recommend
this, then it is good enough for you to
recommend as well.
Clause 2.6.3.1 specifies that in residential
installations RCDs be fitted to final sub-
circuits supplying one or more socket
outlets, lighting points and directly
connected hand-held equipment.
Clause 2.6.3.2 specifies RCDs in “other
installations” for final sub-circuits supplying
socket outlets not exceeding 20A, lighting
not exceeding 20A and directly connected
hand-held equipment.
Workplace health and safety
legislation may override the Wiring Rules
requirements for “other installations” in
which an RCD is not required for socket
outlets rated at 20A amps or greater, but
they are used in hostile environments.
To ensure the safety of workers, an RCD
seems to be a minimum requirement for
any electrical equipment or situation.
For patient areas in hospitals, medical
and dental practices, and dialysis areas –
plus home care and ‘self-harm’ areas – the
Wiring Rules refer the reader to AS/NZS
3003. This Standard has special installation
requirements, including RCD protection,
above and beyond the Wiring Rules. You
will need a copy to ensure all additional
requirements are fulfilled.
Gary Busbridge suggested in the
Autumn issue of
Electrical Connection
that
we will again see increased requirements
for RCDs in the next revision of the Wiring
Rules, with the installation of RCDs being
required on all final sub-circuits.
CONCLUSIONS
Overload, short-circuit and RCD
protection that operates automatically is a
must to ensure safety and prevent damage.
Failure to adequately protect an electrical
installation will place people within the
installation at risk and the electrician will
breach the Wiring Rules requirements and
the law as Wiring Rules are called up in
State-based Regulations.
RCBOs is the most common form of
protection to cover overloads, short-circuit
and residual current faults. RCBOs are
recommended for all final sub-circuits and
electricians should take every opportunity
to replace rewireable fuses and circuit
breakers with them.
Finally, protection options require a little
thought and planning by the designer
and/or electrician to ensure safety and to
minimise the extent of the loss of supply if
a protective device was to operate.
> Power Logic
www.powerlogic.com.auInadequate protection will have
serious implications if something
goes wrong.