Testing Ze when you cannot disconnect the bonding?

[buzzlightyear]

I have no need to actually test anything, but I am curious to know how a professional electrician would perform a Ze measurement if he encoutered this arrangement

either by measurement or calculations.

 

[ferg]

I think if you look at it again there is an earth terminal block next to the cutout and the seals have fallen off.

That photo must be an optical illusion.

 

[davepusey]

I think if you look at it again there is an earth terminal block next to the cutout and the seals have fallen off.

That photo must be an optical illusion.

Here is the whole box if that helps?

 

[ferg]

Here is the whole box if that helps?

I see my sense of humour has fallen flat on it's arse agin.

 

[buzzlightyear]

see my sense of humour has fallen flat on it's arse agin.

But which one, its a bit cheeky saying that. any nobody like a smart arse.lol.

 

[davesparks]

The other option, although not ideal, is to test and record that Ze was taken with parallel paths in place. This happens more so in commercial and industrial settings where the supply cannot be shutdown for financial reasons.

That is not Ze, that is a Zs measurement.
[automerge]1592940600[/automerge]

That's what I would have expected to be done. Although would it really be necessary to connect all three of the original wires that now just go back to the cut-out? Surely one would be enough and the other two, now redundant, wires could be cut back flush.

Every time I have come across this it has dated back to the days when 6mm main bonding was installed so all 3 conductors are 6mm.
Now the conductor from the service cutout to the MET should be 16mm for a PME supply (which this is as per the label)
So if they are 6mm then all 3 would need to be connected to achieve the ideal 16mm CSA.

 

[Taylortwocities]

either by measurement or calculations.

If I remember from my college course many moons ago, you can also request the Ze figure from your local, friendly and ever helpful electricity supplier.
I've never tried it though. Anybody else had success with this?

 

[davesparks]

If I remember from my college course many moons ago, you can also request the Ze figure from your local, friendly and ever helpful electricity supplier.
I've never tried it though. Anybody else had success with this?

They will give you their nominal design limits, which are usually also available from their websites (buried somewhere, if you look hard enough)
For example 100A TNS will normally be quoted as 0.8ohm
100A TNCS will normally be quoted as 0.35ohm for existing supplies or 0.25ohm for new supplies (this is true for UKPN at least, not sure if the others work to 0.25 now/yet)

 

[Taylortwocities]

Yes. Those (IIRC ) are the standard figures from DNO Engineering Recommendation P23/1 - which, I believe, is the origin of the 0.35 and 0.8 figures.

 

[7029 dave]

T bar straight through them knock outs.