TT Zs measurement

[Empire]

Morning all,

I’m slightly confused with a submain TT out building radial extension.

Earthing arrangement to property is TT

outbuilding has its own local spike and 16mm to submain board.

Zdb to local spike is 6.5 ohms
Pssc of 4mm sub main feed 0.6 ohms
r1+r2 of radial circuits is 0.3 ohms

final Zs of circuits is 14 ohms

performing a 2low Zs produces a satisfactory 7 ohms.

So the issue is the neutral path of the 3low measurement.

does anyone have an explanation please?

 

[Strima]

Pssc of 4mm sub main feed 0.6 ohms

This should be measured in amps not ohms.

 

[Empire]

tremendously helpful.

thanks

 

[radiohead]

Low current Zs tests are notoriously inaccurate.

 

[Empire]

Ah, ok. Thanks

 

[cliffed]

Psc 3.6ka On .6 ohms.
Thats a low reading,for a tt systen,parallel I expect,but ok.
Why are you interested in the neutral path,basic TT system,back to the transformer.

 

[Empire]

Psc 3.6ka On .6 ohms.
Thats a low reading,for a tt systen,parallel I expect,but ok.
Why are you interested in the neutral path,basic TT system,back to the transformer.

thank you,

the volts are high too, around 250 so it must be actually sitting on the transformer.

really It’s just professional curiosity and the fact that it ruins the look of the tabulated figures .

After ze and pssc and some mental adjustment giving a ballpark measurement for the final zs after including r1 +r2. I find the 3 wire zs peculiarly different from the (as expected) 2wire zs. I’ve not noticed it before and I thought someone might have an explanation.

it’s taken many hours and many resets to be able to make this reply and I can’t be doing with that, so it will be my last.

I shall keep reading just in case a clue to this anomaly is found.

TIA.