No ze at origin of tt system

[Adam Jackson]

Hi guys, cannot get a resistance reading when using my Robin loop tester. It just shows 204v and the red do not proceed lamp lit.
Never come across this before any ideas would be appreciated. (The live neutral reading is 243v)
New rod fitted and driven in to good ground at about 2.3 meters.

 

[gnselectricals]

Sounds like a high resistance earth/no earth. Is the installation all isolated and testing between the main supply? Could be an earth fault somewhere in the installation

 

[Bobster]

Where are you testing at?

Do you have any way to test the rod.

Oh an it's Ra

 

[Adam Jackson]

Yeah installation isolated and testing at main 30ma cut out switch and earth rod.
Havnt got an earth rod tester as normally do it with the loop tester.

 

[Octopus]

Water the ground and try again.

 

[loplug]

Where is the installation? Can you see the supply transformer? Is the rod in good ground ie not made up/ back fill. Out of interest is the old rod still in place could you test that for reference. Have you in stalled a new earth conductor or reusing existing? If you are testing remote of the rod then what earth continuity reading did you get ?

 

[Wilko]

Hi - only basic thoughts, sorry - confirm rod actually connected to met (wander lead). Confirm tester (test at another site, check batteries). My KT65 measured a TT earth loop over 300 Ohms last week, it was corrosion at the rod to cable connection, thankfully .

 

[westward10]

What Robin tester is it.

 

[Ian1981]

Could be like mine was today

 

[Adam Jackson]

I can see the supply tranny and the rod is new and gone in very good ground. The old rod was giving the same problem so cant use that as a reference. Just never had this before. My only thing i can perhaps think of is volts drop but line to neutral reading comes up as 243v so no problem there.

 

[Ian1981]

If you are attempting to measure the resistance of the electrode that connects to a generator you need an earth electrode tester as the rod will be referencing the generator neutral to earth.
Attempting to use an earth fault loop impedance tester will not work as the electrode doesn’t form part of the earth fault loop impedance path.
Either that or I have misunderstood your post.

 

[westward10]

As in #7 have you done a continuity test of the earthing conductor to the electrode.
What Robin tester is it.

 

[Adam Jackson]

My Robin loop tester is KMP 4120L. Checked continuity of met to rod is ok (3meters of 16mm).
Ive never had a reading of 204v when checking the ze on a tt.

 

[Wilko]

Try measuring voltage L-E (rod) and N-E, maybe that will shed some light?

 

[westward10]

That tester will measure up to 2000 ohm and it is unusual to get a do not proceed indicator unless polarity is incorrect or you have an almost non existent earth, I use one day in day out.

 

[HappyHippyDad]

Barring any inaccuracies to the measurement I guess the soil resistivity could be very, very poor?

Could you try connecting the new rod to the old to see if that improves the Ra?

Also, could you try an RCD trip test on the RCD? If it trips then you know your measurement of 207V is incorrect and therefore not being measured accurately (as I dont think the RCD would trip if only 207 V L-E). Not sure about this last paragraph though! Just a thought.

 

[HappyHippyDad]

Barring any inaccuracies to the measurement I guess the soil resistivity could be very, very poor?

Could you try connecting the new rod to the old to see if that improves the Ra?

Also, could you try an RCD trip test on the RCD? If it trips then you know your measurement of 207V is incorrect and therefore not being measured accurately (as I dont think the RCD would trip if only 207 V L-E). Not sure about this last paragraph though! Just a thought.

 

[Adam Jackson]

Just to update on this problem. I thought i would walk down the road to the cottage next door to ask if i could plug my loop tester in a socket to see what reading i got and low and behold it read 201v. So looks like transformer problem, as got talking to them and they said they lost power earlier in the year due to lightning. WPD sending someone to look at transformer.

 

[Adam Jackson]

Just to update on this problem. I thought i would walk down the road to the cottage next door to ask if i could plug my loop tester in a socket to see what reading i got and low and behold it read 201v. So looks like transformer problem, as got talking to them and they said they lost power earlier in the year due to lightning. WPD sending someone to look at transformer.