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Slightly OT: Inverters and earthing

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 faulty.

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.

Views?

Glenn

Reply to
Glenn
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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.

Reply to
Davo

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.

Reply to
Mike Manuka

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.

Reply to
terryc

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.

Bye. Jasen

Reply to
Jasen Betts

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.

Cheers Glenn

Reply to
Glenn

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)
Reply to
The Real Andy

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.

Reply to
The Real Andy

ide quoted text -

Yo,

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....

Reply to
j.l

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