earth loop readings

[oxford 12]

Just done a test on a TT system,and got 150ohms on the rod.But got 0.33 on the cooker circuit.
Am i right in thinking the Zs readings are such due the main bonds bringing the resistances down,never had this before

 

[Top Cat]

If you have an old lead water or gas meter it could really bring the reading down, bit like having a 500 yard earth rod. Saying that i have never seen it go down that low on one of my jobs.

Edit:- should have said pipe not meter!

 

[StuSpiers]

I have a street up the road from me.

All TT and get Ze readings of 0.24 (that is true ze)

Built them in 1920 - dont know what they used for earth but it works well!

Yhea as TC said no reason why services wouldn't bring that reading down to 0.33

 

[Adam]

I have a street up the road from me.

All TT and get Ze readings of 0.24 (that is true ze)

Built them in 1920 - dont know what they used for earth but it works well!

Yhea as TC said no reason why services wouldn't bring that reading down to 0.33

Are you sure they are still TT's?
I have seen a few properties supplied by overhead lines that are actually TNC-S (PME) supplies.

 

[oldtimer]

Have you tried to test th Ze at th CU with the main earth disconnected ? yes disconnected this will tell you if you are getting another path ie through the gas water as there may be another property near by that has a good earth and is exporting it to you property but you may find that you can loose it if the gas/water company turn up to lay plastic pipes.

 

[Engineer54]

I have a street up the road from me.

All TT and get Ze readings of 0.24 (that is true ze)

Built them in 1920 - dont know what they used for earth but it works well!

Yhea as TC said no reason why services wouldn't bring that reading down to 0.33

In the 1920's, Electricians actually knew how to make a good TT system!! lol!!
They would have been using long (9/10 foot) rods too, or even scaffold poles, definitely not these modern 1m twigs..

But as others say, probably a good portion of that low value would be attributed to those old lead pipes, but then that would be the installations Zs value not a Ze value...lol!! Having said that, i can show you TT installations in parts of Essex, that are both very old and relatively new with sub 1ohm values similar to those quoted above... All at the end of the day, depends on soil/ground conditions and how deep the earth rods have been driven...

 

[somersetsparks]

Many farms have very good zs readings as with all the bonded steel buildings, steel grids in floors etc. I have seen lots below 1 ohm.
On demolition of an old military building before, we found a 10x10' earth plate!

 

[jacksonwilliam]

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[Fin170]

In the 1920's, Electricians actually knew how to make a good TT system!! lol!!

You're joking right? Most of the villages around here use the same system of 'found old pipe' waked into the ground immediately outside the house. Mine is still there (haven't got a result off it) and I know a few still in service + a few I've removed and they're all rubbish!

 

[Engineer54]

You're joking right? Most of the villages around here use the same system of 'found old pipe' waked into the ground immediately outside the house. Mine is still there (haven't got a result off it) and I know a few still in service + a few I've removed and they're all rubbish!

No i'm not Joking!! Some of the old village electricians may not have been too clever, but in the main, they knew far more about making a good TT system than most electricians today. Virtually every installation outside of the bigger towns and cities were all TT systems in those days. There standard was below 10 ohms, your standard is below 200 ohms, so you tell me who's systems are ''Rubbish'' ??

Think about it just for a second or two.... Your talking about installations that were made neigh on a 100 years ago!!! Do you honestly expect any domestic TT ground electrode to be still anywhere near 100% serviceable?? One things for certain, there would be very little if anything left of the 1m twigs your using today in a 100 years....

 

[somersetsparks]

No i'm not Joking!! Some of the old village electricians may not have been too clever, but in the main, they knew far more about making a good TT system than most electricians today. Virtually every installation outside of the bigger towns and cities were all TT systems in those days. There standard was below 10 ohms, your standard is below 200 ohms, so you tell me who's systems are ''Rubbish'' ??

Think about it just for a second or two.... Your talking about installations that were made neigh on a 100 years ago!!! Do you honestly expect any domestic TT ground electrode to be still anywhere near 100% serviceable?? One things for certain, there would be very little if anything left of the 1m twigs your using today in a 100 years....

I assumed they were copper once till I took them in with my scrap and they stuck to the bloody magnet!
The state of 3/8" electrodes after just 2 years is pretty bad, rusting nicely especially at ground level, I inspected a couple I disconnected a couple of cabins before, pretty shocking when you think that some permanent buildings rely on them!
On our firm we only use them as temporary stakes for cabins gennys and the like.