TT Help

[easysushi]

Alwite lads,

Replacing a consumer unit today in ex council house. Got Earth fault loop of 537 Ohms, after playing around and finding the electrode which was a steel pipe I replaced the Eath cable from 10mm to 16mm and drove a 1.2 mtr copper rod in got a value of 410 Ohms. Then drove another in the front garden lawn dropped to 360, stuck another in got 300, stuck another in got 200, stuck another in got 130Ohm.
So i have got 5 rods in the ground at the moment. Obviously the customer is not to keen to have so many inspection pits in there frount garden .

Any Ideas would be very much appriciated, or am I missing something
incoming supply is over head


Cheers


Ty

 

[Andyfm]

Have you enquired if PME is available

 

[lamb]

Depending on the soil conditions you may be better off with a different type of electrode altogether, eg. a plate or tape electrode, or a much longer driven rod electrode.

 

[mark80]

Just use a time delayed 100mA main switch to cover the whole installation!

 

[m4tty]

Just use a time delayed 100mA main switch to cover the whole installation!

Can you explain why mate please. Just trying to learn cheers

 

[easysushi]

Have you enquired if PME is available

PME is not available. Enquired with the neighbours also, they constantly have RCD nusiance tripping. The RCD's are fitted befor the CU


Cheers


Ty

 

[lamb]

Assuming you are using an insulated dual 30mA RCD consumer unit, there is no need for a 100mA RCD.
The 30mA RCDs would give a max. permissable Zs of 1667 Ohms in theory, but you must achieve an electrode Ra of <200 Ohms to ensure stability of the earthing arrangement.

Personally I would use rod electrodes with threaded ends and screw-on couplers, keep driving them in and joining new lengths on until a satisfactory reading is achieved, then dig a hole around the top and install a pit and lid.

 

[easysushi]

Assuming you are using an insulated dual 30mA RCD consumer unit, there is no need for a 100mA RCD.
The 30mA RCDs would give a max. permissable Zs of 1667 Ohms in theory, but you must achieve an electrode Ra of <200 Ohms to ensure stability of the earthing arrangement.

Personally I would use rod electrodes with threaded ends and screw-on couplers, keep driving them in and joining new lengths on until a satisfactory reading is achieved, then dig a hole around the top and install a pit and lid.

Mate I know it has to be <200 Ohms but what would you consider to be and accetpable reading with a single rod, ok maybe 4 x 4ft rods linked together.


Cheers


Ty

 

[lamb]

Depends entirely on the soil conditions, 90 percent of the time I get below 200 Ohms with a single 4 foot rod. In your case sounds like you have soil with high resistivity so it's gonna be hard work whatever you do, eg. very long electrode, multiple electrodes, plate or tape etc.

 

[nickblake]

just did a caravan and the readings were 36 ohms with a single 38 mm rod , have a look round and find what looks like a damp spot , one of the best places ive found is near sink outlets or down pip[e gullys because that area tends to always be damp

 

[easysushi]

Depends entirely on the soil conditions, 90 percent of the time I get below 200 Ohms with a single 4 foot rod. In your case sounds like you have soil with high resistivity so it's gonna be hard work whatever you do, eg. very long electrode, multiple electrodes, plate or tape etc.

The soil around the area is very sandy. I gues that would give cause to high resistivity do you think


Cheers


Ty

 

[nickblake]

yes im affraid it would , i did a temp caravan supply in a sandy area by a beach couldnt get a decent reading in the end i ran a 25mm earth 30 meters and sunk it in a stream got the reading down to 76 ohms , try a rod as close to the house as you can yu may get better readings also try lower ground so any water runs in it , the wetter / damper the area the better , could be an idea to use a tape or plates to

 

[Plonker 3]

Pour a bucket of water around it just before testing

 

[easysushi]

Well 4 rods later and sweating like a ******, driving the rods down got 69 Ohms. A lot better then the 500 I had to start with

Thanks for all your advice guys


Cheers


Ty

 

[nickblake]

Nice one