earthing arrangement

[bks]

Why it would be better off Changing tns to tt and comply with reg. because of not having reliable earth. When installation was tns earthing with Ze 18 ohms because swa was used as earth is corroded and 22ohms after changed to tt. Intallation is rcd protected before and now. Can anyone help me to understand about this principle change tns to tt. Except spending fortune to replace that swa to 3 core to keep tns. Client doesn't want to spend more.

 

[Plonker 3]

Why not just inform the DNO of the problem who will repair it free of charge. This is a urgent matter that needs addressing ASAP.

 

[sparks1234]

Why it would be better off Changing tns to tt and comply with reg. because of not having reliable earth. When installation was tns earthing with Ze 18 ohms because swa was used as earth is corroded and 22ohms after changed to tt. Intallation is rcd protected before and now. Can anyone help me to understand about this principle change tns to tt. Except spending fortune to replace that swa to 3 core to keep tns. Client doesn't want to spend more.

If the earth is unreliable thats a risk, if the 0.18 is not guaranteed and wanders you cannot rely on it.
As long as you get down to an acceptable level of Ze on your earthing rods this should be a reliable earthing system.
The reading may well change from summer to winter on your earth fault path so be aware as to the time of year that you are installing it, so if you are on the high side and the ground is as wet as its going to get then during a dryer season the Ze reading may well go higher and become unstable.
I dont do much in the way of TT systems but I think the maximum reading should be 200 ohms but really you should be looking to get substantially lower than that.
There is a certain person on here that will give you a whole lot more info on earth stakes etc but I'll mention no names.
Check with others on the maximum limits of a TT system

 

[Marvo]

It sounds like you've already done a TT conversion. As Dilb says the earth on a TNS would have been the DNO's responsibility to provide remedy but if you've converted it I'm not sure where you stand plus the DNO's distribution network records would now be incorrect.

 

[Guitarist]

Another "electrician" who's not sure what to do, or a DIY'er?

 

[bks]

Thanks folks for your reply but this problem I am having in the caravan park which is from one of the DU to the chalet, not from the supply origin which is DNO 's responsibility.
I just want to know what reason changing tns to tt would be better off if the installation has high earth even installation is already rcd protected and without replacing cable.

 

[Plonker 3]

Hang on so the Ze reading you are giving us actually a Zs from the caravan?

 

[bks]

Yep. Actually it's to the chalet.

 

[Octopus]

So the most important question is "where is the swa running from and to?"

EDIT: So you as the park owner has this issue. How long is the run to the chalet?

 

[Marvo]

but this problem I am having in the caravan park

That kind of information should have been in the opening post......

 

[PEG]

If,as you have said,the unreliable earth reading is due to a corroded armouring,then THATS your immediate problem. Now can i have the first week in August for free? :tounge_smile:

 

[Engineer54]

The SWA has corroded because the cable wasn't laid correctly in the first place. The sheath of the cable has been compromised, probably due to cable being laid in the trench, with the presence of sharp stones/debri and being backfilled with the excavated soil that is also laden with sharp stones, etc!!

You now have 3 choices, 1) replace the SWA cable, 2) install a suitably sized separate CPC, 3) TT the cabins installation. The 3rd choice would be my last choice, unless you are prepared to put a concerned effort into getting a lower single figure Ra value....

 

[bks]

still i didn,t get the answer what i am looking for

 

[spark 68]

still i didn,t get the answer what i am looking for

Several people gave you the correct answers, or is that not the answers you wanted to hear ?

 

[Engineer54]

still i didn,t get the answer what i am looking for

What exactly are you looking for then??

You were asked where the cable is running from and to?? Is it from an adjacent hook-up unit to the chalet or from a central distribution DB to the adjacent hook-up unit, where the SWA has corroded away??