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domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 01:02pm 28 Sep 2013

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Hi,

Switching from mains to generator and back, I noticed the automatic/manual changeover or transfer switches also make/break the neutral and I refer here to 240VAC.

Any idea why this safety feature is performed as the neutral is hooked up to earth anyway in those domestic MEN (mains, earth, neutral) systems?

Earthing: The generator has an earth connection to its frame but that is obviously not good enough as it may rest on rubber wheels. The earth for the house supply is an earth stake and that is the correct earth. Is the house earthing system good enough in a generator setup and can it be used?

Relax, I am not going to kill myself or others!

Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.

Winston Churchill

M Del
Senior Member

Joined: 09/04/2012
Location: Australia
Posts: 155

Posted: 04:44pm 28 Sep 2013

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I am a VM, not an electrician. When we set up gen sets in the field to power our maintenance vehicles the vehicle and the gen set both get earthed.

It does not matter the size of generator (2kva-32kva), or if the gen set is trailer or ground mounted.

For some reason the earth leakage system did not work if the gen set was not earthed.
When the vehicles were connected to a building supply sometimes the building would trip before the vehicle when tested.

Hope this helps.

Mark

domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 09:23pm 28 Sep 2013

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Thanks for reply. Have also read that the RCD will trip in such situations. Reminds me of Fremantle TAFE: When all students switched on their PCs at the same time, the RCD would trip as the sum total of the leakage of 20 PCs would be sufficient to trip.

Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.

Winston Churchill

yahoo2

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Joined: 05/04/2011
Location: Australia
Posts: 1166

Posted: 05:33am 29 Sep 2013

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I will have a go at this one, not easy to explain without quoting chapter and verse regulations.

Most single phase small generators are sold as jobsite gensets. this means they are wired to comply to run with no earth stake so the neutral winding is bonded to the generator frame.
When you power a house with an unswitched neutral you end up with an earth at two points that may be floating at two different earth voltages connected in a loop through the neutral wire and the soil. The flow of current can trigger RCD's

To fix this, on a permanently wired generator the bonded neutral used to be removed from the generator frame but in most situations this means the unit is not compliant to the new regulations.

Transfer switching the neutral complies with the regs BUT there need to be some thought put into exactly where and how earth straps are fitted or the arc fault detection on some system components is bypassed and non-functioning.

I'm confused, no wait... maybe I'm not...

domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 01:16pm 20 Oct 2013

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Thanks yahoo2. Found some more interesting stuff via google with wiring diagrams picked up from AS/NZ 2000. Different for permanent/non-permanent installation of a generator. Transfer switch must be of the interlocked type, writing must be red on white, etc. The link to the co. with name Hager seems to be broken to get a look at its transfer switch. A DIN rail mounted one costs about $90 with postage and switches neutral an active from main to generator.

Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.

Winston Churchill

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