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noneyabussiness
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Joined: 31/07/2017
Location: Australia
Posts: 513

Posted: 12:26pm 26 Oct 2017

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Just asking the professional people on here their opinions on this, i have a off grid connection in my shed that has its own grounded ( rod, ETC) Men system... it is currently isolated from the main (the house) i want to run the air cons in the house again isolated from mains but the grounding system will then be neutral tied.. will i cause any issues if the neutrals are tied together? ? I want to keep the system as safe as possible, if im looking at it wrong could you please advise? ?

I think it works !!

Boppa
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Joined: 08/11/2016
Location: Australia
Posts: 814

Posted: 01:33pm 26 Oct 2017

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First- legally, anything to do with your grid system requires a licensed sparky to work on it! (fines can apply and they arent small)

Now with that out of the way- Any changeover switch used to switch between grid and offgrid (be it genny, inverter whatever) MUST switch both the active and the neutral

So although the houses earth and neutral are linked at the fusebox, the neutral has to be broken before that link so that when the switch is in the offgrid position, its neutral is in fact no longer connected to the neutral supply lie or the earth bus but to the offgrid source only

A changeover switch must also be a 'break before make' dpdt switch ie it MUST positively open the first set of contacts before closing the second to prevent any possible linking of the two power sources and must have adequate isolation values
(marine suppliers often have rated switches for the job that are legal to use,as do electrical wholesalers- often called ship/shore power selector switches)

Technically, the earth systems should be tied , but the supply authorities frown upon multiple earth points (although I have heard of some places doing it, was always told in the past this was a definite nono) as this could set up circulating currents through the earthing system

The best solution (in fact the only legal solution) is to get a sparky in to fit the switch, (dont mention your offgrid system at all), and ask him to fit the switch and a flying lead (extension cord plug or a wall mounted socket similar to the one caravans use) so you can run a standby genny if required, then plug into that once he's gone... its a common enough request and wont raise eyebrows or the inspectors ire if they see it- and wont land you with a big fine if they do inspect your grid boxEdited by Boppa 2017-10-27

noneyabussiness
Guru

Joined: 31/07/2017
Location: Australia
Posts: 513

Posted: 02:22pm 26 Oct 2017

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So, what your saying is keep both systems TOTALLY separate. .. including earth rod.... because i am still using the grid for everything else, when i have enough to go completely off grid i will be doing the above with a change over switch (we did that on my brothers totally off grid setup )... makes sense but i just wanted to check...

Thank you Boppa for your sage advice

I think it works !!

Boppa
Guru

Joined: 08/11/2016
Location: Australia
Posts: 814

Posted: 04:25pm 26 Oct 2017

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The earths are going to have to be tied, I wouldnt feel happy with the idea of relying on the earthing system being separated, and switching it- no- definitely not!

Just that until recently having multiple earths was a nono, but that seems to be different now

So definitely tie the earths but not the neutrals (or the actives!)

eta

Actually if a sparky fits the socket, it would be joined at the socket to the house earth, so by simply using a 15A extension cord, it would end up earthed at both points anyway so not an issue
Edited by Boppa 2017-10-28

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