Unknown Earth

[stidge]

hi all,
Been to clients house today to carry out some work,Overhead supply(row of council houses)but cant find anywhere an earth spike.Gas and water bonded.There is no Pme visible at service cutout just L&N coming into house.Took a ZE reading which was .34 (sounds like PME to me)I Rang Helpline for some advice and was told to contact provider to see if PME at Transformer End!Never come across this before!.Several calls to provider and still none the wiser!.Has anyone come across this before?Any advice?What do i put on cert as circuit altered passes fine,diconnection times etc etc.Any advice greatly appreciated

 

[ezzzekiel]

assume you took ze at neutral in service head? otherwise if there is no earth then where could you take it?

.34 would fit for pme although on the top end

 

[Tunnel Sparkie]

Has the property been re-wired lately? The reason why I asked this is because the gas and water supply pipes would have been used as the original earth on the property, with the original pipes being lead.This practice stopped in the early seventies and a proper earth spike was installed.I had similar problem like this, I went to a property which had no earth on it and found no main earth point. The house had just had a new plastic water supply pipe installed which removed the only earth on the house through the water pipe. I had to install an earth rod and a 300ma R.C.D. to achieve the correct disconnection time. These days a 30ma R.C.D. Would be fitted I hope this helps you out.

 

[mogga]

silly question time ?? where did you get the Se from if you couldnt find a main earth connection? Might just be me not reading Op correctly Appoligies if Iv missread something ?

 

[Des 56]

Is the main earth visible in the consumer unit, along with the service bonds
As mogga asked,where was the Ze taken

Without veryfying that the main earth exists, I suppose its possible to have no main earth,plastic services a neutral earth fault and a Zs reading that equated to Pme, by getting the reading via the fault and the neutral of the supply

 

[ezzzekiel]

silly question time ?? where did you get the Se from if you couldnt find a main earth connection? Might just be me not reading Op correctly Appoligies if Iv missread something ?

my thoughts and can only think of inside neut term at service head if its pme otherwise cant see where a ze is possible?

got me baffled

 

[JUD]

assume you took ze at neutral in service head? otherwise if there is no earth then where could you take it?

.34 would fit for pme although on the top end

+1

If there is an earth in the CU, which there should be if you've been able to take a Ze reading, where is the other end connected?

 

[scotsparky]

could this be a tn_c system using metalwork of D.B as link between neutral and Earth? it would mean that there would be a low reading and no earth cutout at cablehead.

 

[Tunnel Sparkie]

Original I only went there to change some sockets, but when I went to test them, I had no earth path so a little job turned into a much bigger job. After fitting the earth rod and the R.C.D. I took the reading from the new earth rod. The property was T.T. supply, there are probably 1000's of homes in the U.K. which have had new gas & water fitted and have lost there Earth path.You should make a comment about it on your test certificate that further investigation is required as you are unable to find the M.E.T. Which should always be close to the Main Incoming supply.Hope thi helps you out.

 

[JUD]

could this be a tn_c system using metalwork of D.B as link between neutral and Earth? it would mean that there would be a low reading and no earth cutout at cablehead.

TN-C is not permitted on consumer's side

 

[scotsparky]

jud i know but it still exists and possible in older buildings. just an idea that would explain both no earth visible but low ZS readings.

 

[Des 56]

If there is no main earth and a low Zs
If there was Tnc-s next door and shared metalic water or gas services and both houses bonded, then the reading could be coming from next doors supply

 

[stidge]

Thanks lads will go back tomorrow and disconnect all earths,do another ze.Thinking now could it be a decent reading off the water pipe if that was original earth? just baffled me as no 100ma rcd at cu and i would say property not been touched since built! What would you put on DIC as customer wont pay for upgrade off board or Front end RCd. I have added RCD spur to lighting cct i have altered.Thanks again

 

[JUD]

Stidge, where have you taken your Ze reading from?

Is there a main earth in the CU, if so where is the other end?

 

[stidge]

dont think there is main earth took reading off earth bar the gas water are in 16mm