Slightly OT: Inverters and earthing

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I'm seeking views on whether an inverter powered system (in a bush
shack) should be earthed or not.

As I understand it, the Australian domestic electricity supply is a
multiple earthed neutral (MEN) system with the supply neutral earthed
by the electricity distributor and similarly earthed at the consumer
end through a connection between neutral and earth through each
consumer's earth stake.  Hence, one side of the supply (the neutral)
is always at earth potential, even if the consumer's earth stake is

In an inverter system, neither supply line will be at earth potential
nor should there be any risk of current flow to earth in the first
place (unlike a normal domestic electricity supply).  It seems to me
there would be little or no protective effect from earthing one of
these lines since contact with either one alone will not result in a
person in contact with ground providing a path for current.  However,
it may be that there is some value in earthing for EMI suppression.



Re: Slightly OT: Inverters and earthing
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You really need to consult the wiring regulations, since they have the
final say regardless of our opinions. My gut feeling is that you will
need to earth the system.

Re: Slightly OT: Inverters and earthing
Depends on the size of the inverter and how you have it wired and connected.

The other issue is the inverter electrically isolated.

In many cases not having the inverter earthed is safer.

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Re: Slightly OT: Inverters and earthing

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Probably not as all earthing doesis in this situation introduce another
return route for electrocution. You might be better seeing if a core
balance unit was useful.

Caveat, you have said nothing about the building and wiring.

Re: Slightly OT: Inverters and earthing
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I'm pretty sure you need a working protective ground, (earth pin on
the outlets connected to the ground stake correctly) I can't say about
the connection of the supply to ground, possibly you don't need that.

There are regulations that cover this, consult someone who knows or
visit a TAFE library.


Re: Slightly OT: Inverters and earthing
Thanks for various posts.  The structure hasn't been wired yet.  The
reason I'm asking now is to consider whether it should be wired in the
conventional domestic supply way or not.


Re: Slightly OT: Inverters and earthing

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I dont have access to the last Australian standards but I beleive that
inverters are now covered under the building site and demolition
standards (electrical installations), which from memory is 3012
(please correct me if I am wrong). Also, the relevant regulation for
gensets is covered under AS/NZS 3010.

The regualtions for gensets does not states that you cannot connnect
it to an earth electrode (ground stake). They do however state that
the generators earth must be bonded to neutral.

They may also be refererences in AS/NZS3000 : 2007, but I am not aware
of this as I dont have access to the latest standards. Pretty sure
there was nothing in the 3000 : 2000

Not sure if libraries have them, or someone here might be able to
quote the lastest regs, but you should do this. The thee standards you
want are 3000 : 2007, 3010 : 2005 (there may be a later version than
2005) and whatever the current building and demolition site regs are
(3012 i think)

Re: Slightly OT: Inverters and earthing
On Wed, 08 Oct 2008 22:38:40 +1000, The Real Andy

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I must also state that all the above is a VERY breif overview of a
single phase genset. 3010 is a full book dedicated to this very topic.

Re: Slightly OT: Inverters and earthing
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Yes you do need to look at AS3010 and AS3000:2007. With regards to
small generators there are several acceptable ways to connect them,
they can be used as an isolated system or they can have an MEN link
and an earth stake. With an isolated system, it becomes necessary to
switch both the active and neutral in all switches (like what is
required in caravans). This most important thing is that you need to
follow an particular earthing scheme properly - you cannot pick and
choose bits of both or you'll end up in trouble. I think generators up
to 25 kVA can be used isolated (neutral not bonded to earth).

For a fixed installation having an earth stake and MEN link will make
the rest of the wiring simpler and also enable RCD's to work - but
this does depend on the inverter. Given AS3000 now required RCD's to
be fitted for all socket outlets 20 amps or under (with very few
exceptions and this installation isn't one of them) and all lights on
circuits 20 amps or under (with I think no exceptions) - this probably
dictates that you need to set it up as an MEN installation. Be aware
if you don't already know that a lot more earth bonding is now
required in a building than what used to be.

Can you get away with a 12 or 24 VDC installation and just have
inverters for specific appliances ? You can purchase standard 36 watt
fluorescent battens that work off 12 VDC and can also get 12 volt CFLs
which seem to work OK. Ceiling fans of course need 240 VAC to operate
so that may be a sticking point....

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