Measurement of Zs in a flat

[Podooser]

If the supply comes in to the flat in question (flat 1) and the supply including the earth (TN-S) goes off to another flat (flat2). How can one measure Zs and Ze without causing any problems for flat 2

 

[Spark123]

You mean they both share the same common supply?

 

[Podooser]

Yes they share the same common supply. The Cable comes in to flat 1 and the tails split- via 2 HRCs into 2 pairs, one pair goes upstairs.

 

[Spark123]

As you need to disconnect any parallel paths i.e. test the earthing conductor in isolation for Ze you should not conduct the test unless all circuits i.e. both flats are isolated.

 

[Podooser]

While measuring Zs will it not create a potential hazard for the other flat?

 

[Spark123]

I wouldn't have thought so if you are using a proper test instrument.

 

[Podooser]

I have an Alphatek MI3000.

 

[Spark123]

A "16th edition" efli tester only conducts the test for a very short period and aborts very quickly if the protective conductor voltage rises by 50v. Hopefully your tester will meet this standard.

Just to clarify, the connection to both flats is part of the clients side of the installation? Not part of the DNOs side?

 

[Podooser]

To clarify, the SWA comes into the kitchen, enters a double HRC arrangement and a pair of tails exit each HRC, one pair enters the meter and the other pair runs up the wall through the ceiling off to the other flat.

 

[Spark123]

So the other flat has it's own DNO supply and DNO earthing arrangement? Sorry, thought you meant they were on a single DNO meter. You'll have to be carefull you don't interfere with the DNO earthing arrangement for the flat above. Where is the earth for the above flat derived from?

 

[Podooser]

The earth for flat 1 comes off the armour (TN-S), but I am not sure yet how flat 2 is earthed. Would it not be also connected to the same armour?

 

[Spark123]

Possibly, is there an earth cable running up with the tails?

 

[Podooser]

Can't tell yet. I have so far asuumed that the earth is run from the same armour but I will be able to explore further next week. Can you explain how Zs/Ze is measured ie. the actual process that the meter goes through.

 

[Spark123]

From what I remember the efli tester measures the supply voltage. It then puts a 10ohm resistor across the supply and re-measures the voltage. It does some sums and calculates the EFLI.

 

[Podooser]

Possibly, is there an earth cable running up with the tails?

Can't tell yet. I have so far asuumed that the earth is run from the same armour but I will be able to explore further next week

The suppliers earthing conductor for both the flats is from the same connection on the incoming supply armour. This needs to be upgraded to 16mm2. Question is does one upgrade only the earthing conductor our flat and will that then comply even though there is still an old earth connection up to the flat above?