Calculating Zs

[sparx northeast]

I need to calculate the Zs for a ring main that uses the metal conduit as CPC. I know that Zs = Ze + R1R2 but I only have an R2 reading as there is no wired CPC. Anyone got a clue?

 

[Plonker 3]

Re: Calculating Ze

Why do you need to calculate it? Have you not got a ELI meter?

 

[sparx northeast]

Yes I have a multi function Megger. The Ze at the time of testing was way over the max allowed. So the local supply company have eventually repaired the supply 2 weeks later and PME'd it to get the reading down. I could therefore only do dead testing at the time and have no intention of going back to re-test every circuit now. I need to calculate all Zs readings from the new Ze and R1R2s

 

[Plonker 3]

Looks like a revisit I am afraid, did you not think of this before you left?

 

[Bobster]

No wired cpc an yet you have an R2 reading?

 

[Pete999]

No wired cpc an yet you have an R2 reading?

It took me a couple of reads but yes you are right

 

[sparx northeast]

Yes I did think about it before I left but with a Ze reading in excess of 2 ohms, what else could I do?

 

[Plonker 3]

What works have you actually carried out on this job?

 

[sparx northeast]

R2 is the resistance of the conduit

 

[sparx northeast]

A periodic inspection

 

[Darkwood]

new/converted supply...new connected mains terminations ... how do you know the DNO hasn't got a bad connection?... you need to revisit to ensure new setup is correct.

You went to test a job ...it failed you called in DNO to rectify issue.

You now need to go retest .... cant see issue here - 2 separate invoices 1 for initial testing 2nd one for testing following supply upgrade.

Obviously its only the live tests to re-do and you can discuss with the customer the second testing will be a reduced cost visit.

 

[sparx northeast]

Nice thought but it's a school and they ain't gonna pay twice

 

[Plonker 3]

So why are you altering your results, any remedial works are surely chargeable?

The DNO have done there bit, it's not upto the customer to ask for a retest and pay for it surely?

- - - Updated - - -

You issue cert saying not suitable for continued use, that's all they have paid for unless the remedially work is included I the price they are paying you.

 

[sparx northeast]

Nice thought but it's a school and they ain't gonna pay twice

 

[Plonker 3]

We'll tell them you issued cert as requested and will,have to pay again if they want results altering due to upgrade on DNO cable. Not your problem.