earth rod test

[ambrad]

Hi All

When testing a tt system, if you cant locate the earth rod is it ok to carry out a ze test for that supply and put a limitation in the earth rod section of the test cert.

if not can anyone suggest how to obtain the correct resistance measurement with only the earth cable at the board accesible.

thanks

 

[jamesBoater]

I f you cant find the rod are you sure there is one! and that the water pipe is not being used as the earth?

 

[Richard Burns]

If you are doing an EICR and the rod is under paving or floorboards, then you are a bit stuck, however this would be an operational limitation.
But it is a critical safety point so if you can find it it would help, if you are unable to check the labeling and security of the connection you do not know how safe it is.
But if you are getting a decent Ze reading then at that time it is OK.
Probably a further investigation required.

 

[ambrad]

thanks richard.

do you think the ze measurement would be representative of the resistance reading for the rod, or is this an assumption that cannot be made.

I am happy to put a limitation in the section regarding the type of rod etc but a figure in the resistance of the rod would be good.

Would the ze be this figure.

 

[Richard Burns]

Ze is an acceptable estimate for the true Ra of a rod, the difference in resistance will be likely less than 0.5 ohms (the resistance of the line conductor back to the substation) and will not make a significant difference to the value.

 

[ambrad]

thank you