Earthing A/C Units Centrally?

[shoeless1963]

Me again, usual preface around multiple thanks for previous help from all and sundry. House is pretty much done and most of the issues are resolved with anonymous supplier of home products. One of my mates came over to look and we started debating the wrongs and rights of earthing… me of course using the little (dangerous) knowledge that I have gleaned from this erudite forum. I’ve ended up with local earths for the a/c units, my mate was convinced that doing it centrally was a far better idea. I’d certainly agree and would happily run the additional cables… but for one thing.

I’ve watched the A/C installers like a hawk since the initial installation and all the units we bought – a mix of Mitsubishi Electric and LG – seem to have the same deficiency. The house cabling runs from the local breaker into the splice that the installers make onto the units themselves. This I see as unavoidable – not clear that any form of in-line connector would be any better? – but I’ve not seen to date any third/earth type wire that comes off the units themselves. I’m sure this is right – as I said I’ve checked this as much as I possibly can – and so running one’s own earth cable back to an ELCB seems redundant as there ain’t no earth to connect it to!

Has anyone a different view and what am I missing please?

Thanks in advance as ever - Me

[Crossy]

Look in the instruction/installation manual.

If it has a metal case it will have a ground connection, probably next to the notice saying 'This appliance must be earthed'.

[shoeless1963]

Thanks Crossy... in the midst of writing the post the electricity in the soi went out and I lost my train of thought (TIT after all ). What I meant to say was, they've earthed each of the units locally with the good old fashioned vampire spike.

It was my mate's assertion that there was a better way to do it which involved running the earth back to the ELCB but on reflection (i.e. after he left and I sobered up) I didn't see how that would work without an actual earth/third cable from the unit itself?

Just wondering...

[Crossy]

Most if not all electrical regulations around the world require a single earthing point or Main Earth Terminal (MET) where all equipment grounds and any equipotential bonds are routed along with the main ground rod. This will ensure that all 'earthed' equipment is at the same potential.

Using local spikes is better than nothing, but there are times when this can introduce a hazard (excessive ground differential due to lightning strikes for example) so in a new install it should really be avoided.

The RCD (ELCB is an old term that should really be reserved for the old, voltage operated devices, now phased out around the world) does not need a local ground to function since it detects a difference between the live and neutral current, if they are more than 30mA different it assumes the current is going somewhere it shouldn't (through you) and opens the supply.

This PEA document is worth a look, it précis the Thai regulations such as they are, in Thai of course but plenty of pictures to look at http://www.crossy.co.uk/Handy%20Files/groundwire.pdf if you follow the diagrams in the document you stand a better than even chance of passing the MEA/PEA inspection.

[lopburi3]

The RCD (ELCB is an old term

Now that we seem to have a football team of terms Panasonic on there newest line of water heaters use the term "ELB". It never ends. Memory overload.

[T_Dog]

When the crew delivering the Hitachi AC installed ours, they ignored the green earth wire in the provided junction box. I told them to connect it up but it never happened so I connected it myself after they left. There was a clearly labeled screw connection for a ground wire on our unit.