Ze on earth rod

[wayne]

i prefer measurement over calculation ,just to be sure nothing's amiss

 

[sparkyork]

yeah and i suppose on a minor works your measuring r1+r2 and Zs anyway so yeah at least you know its all ok, regardless of the earthing arrangements.

the above Zs mentioned was comin in at 1.63 ohms, regardless of the 90 odd Ze reading...

question is been on a job today and earth at electrode was 40 ohms and Zs's through out the installation were all averaging between 26.8 - 27.4 ohms, in the regs there are recommended max Zs's etc and also this 1667 ohms thang as well applyig if circuits are protected by 30ma rcd (which they all are in this case)

is it acceptable on a TT DIC to record these high Zs readings in there relevant box? (measured max Zs etc)
and also why on this job am i getting high Zs's yet on the job earlier mentioned in this post they are something like normal?? is this down to parrellel paths again??!!

sorry im going on about stuff!!

rich

bump!

 

[Shakey]

yeah and i suppose on a minor works your measuring r1+r2 and Zs anyway so yeah at least you know its all ok, regardless of the earthing arrangements.

the above Zs mentioned was comin in at 1.63 ohms, regardless of the 90 odd Ze reading...

question is been on a job today and earth at electrode was 40 ohms and Zs's through out the installation were all averaging between 26.8 - 27.4 ohms, in the regs there are recommended max Zs's etc and also this 1667 ohms thang as well applyig if circuits are protected by 30ma rcd (which they all are in this case)

is it acceptable on a TT DIC to record these high Zs readings in there relevant box? (measured max Zs etc)
and also why on this job am i getting high Zs's yet on the job earlier mentioned in this post they are something like normal?? is this down to parrellel paths again??!!

sorry im going on about stuff!!

rich

bump!

Hi Rich, the Zs readings you get are the ones that should be recorded.

There is an easy way to establish if the lower Zs is down to parralel paths (through your extraneous paths) - remeasure Ze but with the main earth connected to the MET, if it is lower then you are using the parallel paths.

Alternatively, reverse calculate you PEFC value to obtain the value of Ze that would be obtained with the main earth connected (note though that these are not 'true' Ze readings, just for the purpose of clarifying the discrepancies in the results)

 

[wayne]

again parrallel paths ,you're worrying too much simplify

 

[sparkyork]

cheers guys! yeah i do worry a bit too much! ive just got me 1st dic and minor works certs from niccy and didnt want any problems! suppose at the end of the day so long as i just carry on testing fully to the regs etc then i cant go far wrong!!

 

[andy8758]

I work alot on older properties, and have noted the following problems with TT installations:
- main earthing cable is too small - replace with 16mm
- main earthing cable very long to earthing rod - find a better spot for earth rod
- old fashioned steel earth rods - replace with new copper rod (4ft length)
- earth rods come in 5/8 inch as well as 3/8 inch - try the 5/8 inch for better Ze reading
- earth rod corroded or otherwise damaged - lift it to check - usually better just to replace.
- Then try other suggestions of adding additional rods.

 

[wayne]

like you 've been taught!!