TT earth query

[slinkybuzzard]

I have an old house, recently fully re-wired (previous owner, registered electrician).
I have live and neutral in, and earth by ground rod. Appears to be TT type system.

After installing new shower room, (fully bonded earth). I was checking earths and noticed a potential difference between taps/shower etc and walls. Variable in size (0.2 to 2.5V)

Checked earth rod pd to ground: was the same (0.2 - 2.5V)

Switched off at circuit breaker: no pd.

Sequential switch on at via RCD looking for earth fault in one circuit, but surprised to see incremental increase in pd between earth and ground. I.e the more current drawn in the house the greater the pd across the earth.

Checked pd between neutral and earth: 0.2-2.5 V.

Is this normal for a TT system, or do I have an earth fault somewhere?


Thanks in advance

 

[ricicle]

It is possible you have an earth fault.What circuits are you increasing the load on to get the rise in PD?
It sounds to me like the resistance of your earth electrode is high.
Did you do the electrical work yourself or did a registered spark do it as work in a bathroom is notifiable.The earthing should have been checked at the time if so.

 

[bernardgreen]

The neutral on a TT is not grounded at the premises. The nearest point where neutral is grounded could be several hundred yards away at the supply transformer.

Any voltage drop along the neutral due to load currents into the premises will apear as a potential difference between neutral and ground.

So the voltage you are reading is possibly acceptable.

With a resistance of many thousands of ohms in the multimeter on volts a couple of thousand ohms in the earth rod will not affect the reading very much.

If in doubt ask the DNO ( supply service ) if that voltage is too high. They may have a "high" resistance joint on their neutral.

 

[ricicle]

Bernard, his voltage reading is between his earth rod and the ground not between N and E

 

[slinkybuzzard]

Thanks guys. Not sure if anyone would understand the way I described the problem.

Very usefull info.

Would seem that my system is within IEE tolerances for TT system, with a well functioning earth rod with resistance in the region of 100-200 Ohms.

Thanks again.

 

[Spark123]

I'm confused, how have you conducted these tests?
I too was also concluding you were measuring N-E.

 

[ricicle]

Would seem that my system is within IEE tolerances for TT system, with a well functioning earth rod with resistance in the region of 100-200 Ohms.

How do you know.Do you have a schedule of test results?

 

[securespark]

What is your Ze?

Have you got a CU set up suitable for a TT supply?

Is your main equipotential & supplementary bonding up to standard?

Are you sure all circuits within the property have an effectively continuous earth connection?

What are the Zs readings from the destination of your circuits, or mid-point of rings?

For these readings, refer to the EIC completed after the rewire.