HELP, testing near Slough.

[Sparky28]

Eng, I have take a 63a supply over to block of units. No water or gas supply into units, just glorified sheds. If you have e-mail I could send over pics if anyone is interested?

 

[wade88]

I think some photos would be immensely useful. Just attach any you have in this thread mate

 

[Sparky28]

How do I do that wade?? Cheers

 

[Des 56]

You really need the advise of the supplier,there is obviously a earthing system in place somewhere
If the suppliers earth terminal is not apparent maybe there is a possibility the whole site is TT

You say readings are within range,within range of what? Are there rcds around or are we talking extra low TT readings for fuses and/or mcbs ?

 

[Sparky28]

Hi DES, I was thinking the same as you, done a earth loop test on a circuit supplied by a b type 20a mcb and the reading was within range of that of the osg for that type of breaker, I have fitted rcbo's for my ring mains and they operate fine.

 

[Sparky28]

supply

This make it clear??

 

[wade88]

So wheres that 16mm earth going? Wheres it come from. Would ideally have a 4 pole isolator on that too

 

[Rockingit]

If that's the main incoming head (no reason to think otherwise) then it must be a TT, surely? There's no earth from the DNO unless for some reason they've split it upstream and delivered it elsewhere (highly unlikely).

 

[Des 56]

If that's the main incoming head (no reason to think otherwise) then it must be a TT, surely? There's no earth from the DNO unless for some reason they've split it upstream and delivered it elsewhere (highly unlikely).

If it is TT then the isolator could very well be doing with a 4 pole

 

[wade88]

Yea that was my first thought, but you cant see where that 16mm earth is going, and can just see a little of it to the left of the board mount, so its hard to determine what it is. TT would be first call looking at those photos. No MET? where have other circuits taken their earths from

 

[Sparky28]

This is the block where the earths for the dis boards seem to run to. I have taken a supply and a earth from one of the disboards in the pic.

 

[wade88]

Earth clearly not supplied by DNO and can be seen to exit at top left corner - TT. So the installation has been earthed via a rod elsewhere

 

[Sparky28]

Cheers wade, I was looking for something obvious, ( maybe obvious to you ) shall I do a Ze test from that earth block to each phase to obtain highest values? Testing the units is straight forward, continuity cpc, polarity, r1 r2 etc I'm comfortable with that. Does that have a different cert?? Cheers

 

[MDJ]

The council have been round and done inspections on building work etc now waiting for certs.

well get on and certify it then

 

[wade88]

No the Ze will be included at the start of your cert. All test results you will include on a common cert.

Yes record highest value. For a TT your looking for a result under 200 ohms

 

[Des 56]

No the Ze will be included at the start of your cert. All test results you will include on a common cert.

Yes record highest value. For a TT your looking for a result under 200 ohms

Other than rcbos for sockets,he has not mentioned whether they are present elsewhere,at the moment he is looking at figures that will probably exceed what is permitted.especially for his supply cable



If you test from that earthing block you will also be measuring parallel paths,you need to find which indeed is the earthing conductor

When you have identified which it is,you then need to decide if the value permits the protection that you currently have for your sub main supply (and indeed for the whole of the installation) or whether rcds are required

 

[Sparky28]

Hi DES,
The supply I have taken to the units is fed by a 63a type c mcb, each unit is fed by a 40a type c mcb. Only used rcbo's on sockets to avoid nuisance tripping from lighting etc.
If I do a Ze test on my newly installed sub main board for units I would be picking up parallel paths from where board is fed so I need to make sure Ze is ok from the source? Cheers