Electrical Connection Autumn 2016

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www. e l e c t r i c a l c o n n e c t i o n . c om . a u 47
BY
GARY
BUSBRIDGE
From a Standards perspective things
are all tickety-boo… or are they?
Among the problems that have
arisen, by far the worst is the number
of fires caused by the DC solar isolator
switches, whether on the roof or on the
wall near the inverter.
The regulator in Queensland has done
extensive work in the field to check
installations and staff were horrified by
the number of dubious quality DC solar
isolators in the systems.
Some brands that caused fires
have been recalled, and you may
have seen the notices. These brands
were of poor quality with ineffective
switching contacts, which would
not have survived the performance
requirements of a DC isolator Standard
in any shape or form.
Given the evidence gathered by
the Queensland regulator, it’s hardly
surprising that there’s a bit of work to
do in tidying up the loose ends.
A recently updated international
Standard for DC isolators is being
adopted in Australia as AS/NZS 60947-
3. It’s highly likely that the DC solar
isolator will be called up in legislation
as a ‘Level 3 or declared article’.
Before being sold in Australia, these
items will have to show compliance
to the Standard and be marked with
the Regulatory Compliance Mark (an
approved product).
It is most important to remember
that the current AS/NZS 60947-3
Standard for DC isolators is robust and
provides the necessary performance
and verification detail for these types
of switches if applied appropriately.
However, it needs further
environmental considerations
specifically related to Australian and
New Zealand requirements.
Some of the detail now being
considered should help with your
selection, so the following should be
considered as a requirement before
buying solar isolators.
(It will be a future requirement,
but this sort of information and
performance probably applies already
to reputable manufacturers’ products.)
First, look for the marking, and
by this I mean the label. It should
preferably be on the front of the cover
so that it can be easily seen after
installation.
The essential information is the
trade name, the catalogue number,
the IP rating (eg: IP56), DC-PV2
classification, the rated current of the
switch in the enclosure, the AS/NZS
60947-3 Standard number and the
mounting orientation.
For your information the DC-PV2
is described as: connecting and
disconnecting PV circuits where
significant over-currents may prevail
and where current flow can be in both
directions; for example, where several
strings are connected in parallel and
to the same inverter, or one or more
strings with a battery.
Second, the product should carry
the manufacturer’s instructions
for the installer. The information
should contain details of installation
requirements for the IP56 outdoor
units, and an indoor unit where it is not
exposed to weather.
There should also be some derating
factors for the rated current based on
the ambient temperatures where the
unit will be installed. This may affect
the ratings of the solar installations.
The cross-sectional size and the
number of cables accepted into
terminals along with specific torque
ratings on the terminals are also
expected to be on the instructions.
Third, there are some physical
performance issues to look for. The
operating method of the switch should
be independent, meaning that the user
has no control of the switching action
within, even though the user operates
the switch.
The switches shall also be suitable for
isolation purposes and able to be locked
in the ‘off’ position.
Fourth, and this is an important
aspect of the installation, you must deal
with the effects of moisture ingress in
the enclosure.
Think about how the conduit is
fitted to the enclosure, as heating
and cooling during the day and night
does cause some condensation in
the enclosure.
To this end, have all conduit entries
to the bottom face of the enclosure
so that any condensation build-up will
drain into the conduit. This has been
standard practice for many a year
among sparkies installing in harsh
environments.
If you want to be sure, drainage
glands can be fitted to the enclosure
that will allow drainage but won’t
compromise the IP56 rating.
The trick is to buy reputable products
for your installations – just like using
a reputable sunscreen to protect
your skin.
> Clipsal by Schneider Electric
There were lots of horror stories of poor
workmanship and lack of service back-up. If
something went wrong, home owners ended up with
no support whatsoever – they were probably left
with just a phone number.