Pir what a pain

[johnney]

Today i was doing a pir for a client after visually inspecting parts of the house it became apparent that a 6mm old cooker cable had been used to supply a ring main wired in 2.5 to the kitchen. Obviously it had been terminated in a jb some where as there was no evidence of a 6mm cable to any of the kitchen sockets.
I tested out the small ring and it was complete, to determine the r1+r2 of the radial/ring i found mid socket of the ring and shorted live to earth and tested the result was 0.12ohms zs at socket was 0.78 ohms my question is have i done this correctly as it is the first time i've came across this situation?,i don't like doing periodics full stop. been a FULLY qualified sparks for 19 years every day is a school day! thanks in advance.

 

[GaryMo]

It would probably be better to connect line and cpc together at the consumer unit and measure between line and cpc at each point, recording the highest value.

What was the measured Ze? Your results indicate a value of around 0.66ohms. Type of supply?

 

[johnney]

Its a tncs and measured ze was 0.20.

 

[GaryMo]

Was Zs taken with a loop impedance meter on a no trip setting (RCD protected sockets)?
If so then that'll explain the high measured Zs reading.

 

[johnney]

certainly was on trip lock saves a lot of time. take your advice on shorting out at mains should have thought of that but that socket had highest zs so tested from there funny thing was ring from end to end was L to L 0.08 N to N 0.08 E to E 0.16 ohms only had 3 doubles and 2 spured singles on circuit

 

[GaryMo]

That would give an R1+R2 value for the small 'ring' of 0.06 ohms.
Assume the length of 6mm t&e feeding the ring is pretty short, around 6 meters? That would account for another 0.06 ohms giving you your total R1+R2 of 0.12 ohms.

 

[johnney]

Thanks gary i could have done it a differant way but what was important was id done it correctly.

 

[GaryMo]

Thanks gary i could have done it a differant way but what was important was id done it correctly.

It certainly is