TT System questions

[kev123]

Have any of you ever come across a TT system that the earth fault loop impedance readings are as good as a TN, TNC-S system?

Ie, falling well within the maximum permitted value of the MCB?

If so, would you then still recommend RCD protection, If there is none?

Cheers

 

[Guest123]

E54 may very well have come across it but I've only ever achieved an Ra of just under 4 ohms so had to fit additional RCD protection anyway.


What type of install do you have this reading on??? multiple rods, mats, tapes etc???

 

[manley10]

Its nice to see such a low reading however if they can plug an ext lead into the downstairs sockets to use outside it has to be protected by an RCD and as good workmanship plus the low cost of RCD's its a no brainer I would fit one.

 

[i=p/u]

if old enough could be earthed using a service pipe or ...

 

[needasparks]

If main bonds not excluded from the test, could it be picking up the earthing off next doors gas/water.

I had one job on a TT out in the sticks, the supply originated from a shed next to the overhead supply pole, I too had a reading of 0.25 which i thought was good for a TT. Fast forward 3 years and customer trenched next to supply shed only to find my earth rod had crashed into the boards earth rod about three metres away from the pole which we did not know was there.

 

[MarkieSparkie]

Only seen this once, the property was in a remote location with it's own private metallic water supply pipe which was used to earth the installation under the 15th edition regulations.

 

[Deleted member 26818]

Only seen this once, the property was in a remote location with it's own private metallic water supply pipe which was used to earth the installation under the 15th edition regulations.

I think you'll find that was in the 14th edition Regulations, not the 15th.

 

[trev]

Once got 0.29. I couldn't believe it ,I had to triple check then check calibration cert when I got home and I still checked again using another meter the following day

 

[DurhamSparky]

i got 0.35 on a rod..

 

[telectrix]

i got a 33lb catfish on my rod once

 

[DurhamSparky]

my rod... ooops sorry wrong forum!

 

[kev123]

It is not domestic, it is a special location and Industrial. The system is supported by Rods/Mats and Tape The Ze value is 0.03 ohms.

Having tested and inspected countless TT systems i have never ever seen anything like this.

 

[dingledong]

i got the local electric compant to convert it to pme for nothing that must be better !!!!!!!!!!!!!!!!!!!!!

 

[kev123]

I doubt they could carry out such a request! the supply is direct from 11/500v - 400v transformers. It would cost a fortune!

ha ha

 

[Engineer54]

It is not domestic, it is a special location and Industrial. The system is supported by Rods/Mats and Tape The Ze value is 0.03 ohms.

Having tested and inspected countless TT systems i have never ever seen anything like this.

That's because someone for a change, has done things properly, someone that understands what it takes to create a good TT system. Very easy in salt marshlands a bit more difficult elsewhere but very much achievable, as you have just found yourself!!!