Lowest Ze on a TT.

[Spudnik]

Afternoon people.

Just finished a PIR on a scout hut with a 3phase 4 wire supply and a very ropey old looking rod buried under the foliage.

Thought to my self, "uh-oh"!!

Did a true Ze and got a reading of 0.81 ohms!!!!!!!!!!!

Been racking my brains all day trying to find out why its so low but cant think or find anything.

All circuit Zs would exceptional as well


So, what have you had on TT's?

 

[Danny Pross]

Could this be something to do with how near the substation is
D

 

[Sintra]

Chec out previous thread i think i still hold the record.

http://www.electriciansforums.net/i...-whats-your-lowest-ze-recorded-tt-system.html

 

[Spudnik]

Chec out previous thread i think i still hold the record.

http://www.electriciansforums.net/i...-whats-your-lowest-ze-recorded-tt-system.html

I thought there was a thread somewhere

BUT yours was on a plate and mine is on a knackered old earth rod with a stranded, uninsulated cable which runs about 40meters to the back of the building,

so i win

 

[Jason Smith]

stranded, uninsulated ? is it doing the biz all along its length then rather than just at the rod ? just a thought?

 

[bluesky]

why only in countryside people normally use TT?

 

[Spudnik]

stranded, uninsulated ? is it doing the biz all along its length then rather than just at the rod ? just a thought?

It was tested at the CU

 

[MarcT]

can i buy that rod off you?

 

[Spudnik]

can i buy that rod off you?

You could do, but i think someone in Australia is using it to support one end of their clothes line

 

[Jason Smith]

sorry mate, thought youmeant that it was un insulated, and ran buried for 40 meters to the rod. I can se what you mean, its one of the old twisted ones that runs through the building to the rod completly uninsulated through out it s length. The only thing I can think of, and I hesitate to say anything to a super moderator, as, factualy i cannot match your experience, ( With supreme respect ) is that I have worked on these, and on their exit throughout the building, they are of course uninsulated but do lay across and make contact with the water pipes etc, I am led to believe that, even if a water supply is not bonded, if a parallel path touches it, it would become an additional earthing rod as its full of water, I would love your coments as still learning and like alll good trademen/craftmen always will be. I can only learn from peeps like you. !

 

[Spudnik]

The Cu is at high-ish level, out through front of building, round the corner and then clipped along the wall along the soffit, then drops down to the rod.

There are loads of dodgy aspects of the install, well some, and ill post some pics if i go back to do remedials.

 

[Des 56]

My own record of the mid twenties is making the leaders nervous I'm sure all I need is
Time gentlemen please

 

[Guest 004]

silly question, but did you disconnect the cable and just test the earth rod?

As it is a 3 phase supply, and the readings are that low, it is very possible that the star point from the transformer neutral has been grounded as well, but as it is TT you still need the earth rods.

 

[Spudnik]

Indeed i did, although i did only test the one phase being used, as the other 2 had CU's connected that were no longer in use.

 

[Guest 004]

interesting, must be hitting the water table..........

 

[Spudnik]

I must admit, the main earth, although uninsulated, was in remarkable condition!

But, alas it has to be replaced.

Not a job im looking forward too as its down the side that is about 2ft wide

 

[bluesky]

just a silly question, why the power provider did not procide an earth line? is that because of high cost?

 

[xraytek]

Afternoon people.

Been racking my brains all day trying to find out why its so low but cant think or find anything.

Are there any nearby buildings that are perhaps PME and providing an easy path back to the transformer?

 

[evilmonkey]

Could be you were extremely close to a substation Jason. Or maybe close to the water table level perhaps?

 

[Jason Smith]

Sorry mate, but trying to learn from you, and everybody else. The Earth may of been measured from the CU, but is it doing the biz for the last 40 foot of itslength, thats why the readings are so GOOD ? Have you tried taking the uninsulated cable OFF the ground and re testing ? I am not competing, I just want to learn, it would be good if you could post the final reasons on here, I am fabulously interested and am hungry for the knowledge regards Jason