zs over 60

[TANNERS]

ive got a tt system, ive installed 2 rods reading 74 ohm neutral to earth
and i'm getting 63 ohms at the furthest light, and similar on any other circuit .
can't get pme
everything is bonded
the board is covered by a wylex earth leakage circuit breaker and a 30ma rcd


what do i do

 

[Spark123]

What instrument are you using to measure the rod resistance (Ze)?
When you say ELCB, is this a voltage or a current operated device?

 

[Lectrician]

Neutral to earth

 

[TANNERS]

robin kts 1620 multifunction

current operated elcb

and measuring continuity from neutral incoming on to the main earthing conductor to the rod

 

[Lectrician]

Use your meter on Earth Fault Loop, earth lead to rod (only rod - disconnect at fuseboard). Live to live, neutral to neutral.

The ELCB you talk about. Does it have any earth connection on it? Why do you talk of two ELCB's/RCD's??

 

[james 29]

What d i do?

The readings are fine for a TT as long as you mean live earth not neutral earth!!!

 

[cozycats]

Ive never tried it but shouldn't N-E be pretty much the same resistance as P-E on a TT installation? Don't know if you could test this Live either!!!

 

[Lectrician]

Using an ohm meter from N to E will work and give and a reading, however it will not tell you the true phase/earth loop.

It will miss the impedance of the tranny winding, and even though the supply is TT, the neutral on the supply side will still be bonded down an intervals to earth, giving parallel paths.

A phase conductor on an overhead supply will also be longer and often larger sized than the neutral. It wont be hugely longer, and probably wouldn't make a huge difference, but the phases are often looped down poles to fuse carriers or disconnectors.

The reading will also be erratic, as the ohm meter is trying to read a loop which will have huge AC currents flowing.

The only method to measure the loop is with an EFL tester, which will put a known resistance between L and E and measure the voltage/current. It will then calculate the impedance.

To measure the rods resistance, a 3 or 4 wire earth electrode tester is required, and has no connection to the supply at all.