confused tns reading

Peter Woodford · Aug 17, 2009

guys,

Im getting confused, done a ze reading L-PE and got 0.46 ohms but on on site guide says should be 0.8 ohms do i just put the reading down on EIC. Or is this o.k

all zs readings are within limits

sparks1234 · Aug 17, 2009

Should be a maximum of 0.8 ohms on a TN-S or max of 0.35 on a TNC-S

saveloy · Aug 17, 2009

Peter Woodford said:
guys,

Im getting confused, done a ze reading L-PE and got 0.46 ohms but on on site guide says should be 0.8 ohms do i just put the reading down on EIC. Or is this o.k all zs readings are within limits

Nothing wrong with that reading, It's only just over half the max Ze for a TNS.As sparks 1234 says 0.8 is a maximum. The lower the better. Put it down on the EIC. Job done

sand-dancer · Mar 18, 2010

0.8 is the Max allowed reading. Your reading sounds fine as it's lower

pevvers · Mar 18, 2010

Peter Woodford said:
guys,

Im getting confused, done a ze reading L-PE and got 0.46 ohms but on on site guide says should be 0.8 ohms do i just put the reading down on EIC. Or is this o.k all zs readings are within limits

Right, this could sound nasty, but it's not, I promise. I just like to help people!

Do you understand what your Ze reading actually is? With a question like "it's not 0.8 like in the OSG" makes me feel like you may not know what you are actually measuring, so if you need some help just ask, as this is pretty basic. I've found that trying to teach people what the numbers on the instrument are when they take a reading helps no end in getting them to understand the basic principles.

But if you need no help, I'll shut my big mouth and bug someone else!

StokieSpark · Mar 18, 2010

pevvers said:
Right, this could sound nasty, but it's not, I promise. I just like to help people!

Do you understand what your Ze reading actually is? With a question like "it's not 0.8 like in the OSG" makes me feel like you may not know what you are actually measuring, so if you need some help just ask, as this is pretty basic. I've found that trying to teach people what the numbers on the instrument are when they take a reading helps no end in getting them to understand the basic principles.

But if you need no help, I'll shut my big mouth and bug someone else!

New to this live testing... so ill ask for people....

When measuring the Ze are you measuring the resistance between the live conductors and earth back to the local substation? because the earth is centre tapped to netural is that the reading????

pevvers · Mar 18, 2010

You are measuring the impedance from the earth conductor to whatever earth you have there (TT - rod, TN-C-S - neutral, TN-S - sheath), then along this earth path back to the transformer. From the centre tapped part of the transformer through the transformer winding to the live conductor and back to your point where you've got your probe on your line (i.e. supply cable, cutout, distribution board).

So just a big long loop, it's pretty simple when you think about it....

Here's a nice picture to show a full Zs path: -