Earth Electrode Resistance

[T&Earth]

Hi Guys

Started working on a TT system doing a partial rewire tested earth electrode resistance Ra == 187.4 ohms! I know its getting close ot the 200 ohms mark, then read artical by NAPIT that BS 7430 advises max 100 ohms should I run new cable to exsiting rod and snik another rod and link them current cable not long to link second rod a metre away.

Any advice would be welcomed

Many Thanks

T&E

 

[DurhamSparky]

sink a second rod or remove current rod and get a deeper one!!

 

[Deleted member 26818]

As above, but would add, just crimp extra cable onto existing cable rether than replace.

 

[T&Earth]

THANKS

Durham Sparky & Spin London thank you for taking the time to reply
Cheers
T&E

 

[Engineer54]

Hi Guys

Started working on a TT system doing a partial rewire tested earth electrode resistance Ra == 187.4 ohms! I know its getting close ot the 200 ohms mark, then read artical by NAPIT that BS 7430 advises max 100 ohms should I run new cable to exsiting rod and snik another rod and link them current cable not long to link second rod a metre away.

Any advice would be welcomed

Many Thanks

T&E

Yes, ....it would be wise to provide a second rod to this TT system!!

I take it the existing rod and your proposed second rod are these pencil thin things, ....if so they are probably not capable of extending and driving deeper. What ever rods you use, they ''Must'' be spaced at the very least, the overall length of the original rod distant to the second rod, and better if 1.5 times.

 

[DurhamSparky]

ideally you install a TT system like the one im working on at present 0.35

 

[Engineer54]

ideally you install a TT system like the one im working on at present 0.35

And you then WON'T be relying on an RCD device(s) for earth fault current protection....

 

[telectrix]

ideally you install a TT system like the one im working on at present 0.35

what are you using for an earth rod, the statue of liberty?

 

[DurhamSparky]

already installed so unsure of depth!

plus its in a garden which over last 2 days has had more than its fair share of water!

 

[Engineer54]

what are you using for an earth rod, the statue of liberty?

If you use these thin short rods you'll never get a decent Ra!! Use decent sized rods and driven to a good depth you stand a fair chance of getting good Ra values. Iv'e seen more than a good fair few sub 1 ohm value's in the Essex area. ...NONE had these paper thin poor excuses for earth rods....

 

[T&Earth]

Hi Engineer54

Thanks for the advice I've purchased a 5/8 inch rods which can be joined together. The current rod has been in 30 years + and is badly corroded.
Many Thanks

 

[woodhai]

Looking for help.

I had a look at a friends flat, he said the walls in his flat were live when he put a Pen type voltage indictaor to the wall. This was after there had been a flood in the flat next door and his walls are soaked, literally. Sure enough the Pen stick did light up but I tested with a fluke and got 34 volts. He showed me an old JB in the kitchen that must have been a socket some time or other but was now above the cooker. The capping on the cables was metal type, (shows how old this is). I measued full mains voltage from the metal capping to earth, this being the bolt head on another socket. I meggered the circuit and found it flat to earth. We chased the wall to remove the capping and cables as the socket is not required, guess what we found, first a hole in the middle which had parted the twin and earths but not punctured them then further up bingo, a nail, through the outer insulation and into the live conductor. The RCD must be knackered as this must have been like this for years, this will be replaced when I fit a new CU.
With regard to earthing, the supply company do not supply an earth connection as the supply comes in from overhead. What is the best option, would it be to put in 2 earth rods in the floor in his shop down stairs, I know his gas supply has just been replaced with a plastic pipe but not sure about his water pipe. What sort of reading is acceptable?

Thanks in advance Ian

 

[telectrix]

use 5/8" screwed rods. fit 2 joined together. measure the Ra or Ze. if you are below 100ohms, that should be stable, but adding a 3rd rod could improve the value considerably. you will need RCD protection on all circuits. it's always a good idea to fit an up front 100mA delay type to back up the 30mA RCDs in the CU.

 

[richy3333]

Shouldn't this be a new thread?

 

[woodhai]

Shouldn't this be a new thread?

Yes I guess it should have been a new thread, apologies for hijacking the original thread, it was my first post