tt at 104

[devlin maguire]

Hi first post and hoping someone may help at a farm I get 104 ohms ZE but machine says X (failed) its a metrel mi3002 I know the book states upto 200 for a TT system so is the tester firmware out of step with UK regs ? also have some DNO,s changed the name of TT systems as I got what appeared to be something different when I phoned mind you I was on mobile black spot and a bit garbled
Dev

 

[vitoboy]

ello bud
as long as ur tester is giving you the reading of 200ohms or less ur good.
are u sure its not saying >200ohms ?
its the number ur after not the opinion of the software as to the right number..
thats what your for init.

 

[devlin maguire]

Hi and ta on reflection and a scour through the tester manual I was probably phased by the big X on the display what with it being a new meter anyhoo is there a possibility that the supply is PNB given its in a big metal barn and would a remote location be a unshared transformer set up any ideas will be great will however check with the supply company
dev

 

[scotsparky]

book says>200oghms for tt as that is considered a stable reading.
however
nic as for >100 which should be possible.
If you have a true reading of 104ohms minus your 21ohms to allow for the DNOs earth rod at transformer that means your earth rod resistance to the main earth bar is 85ohms so its fine.

 

[vitoboy]

whats this 21 ohms off for dno earth rod..
would like to know more....

 

[scotsparky]

Vito as you know

the maximum reading for a ZE for the following systems is
TNC-S is 0.35 ohms
TNC 0.8 ohms.
The supply authoritys also say the maximum reading for there earth rod at there transformer for TT systems is 21ohms.
its handy to bear in mind if the reading is tight but normally you dont need to bother