TT system

[monkeyelectric]

Hi guys got a small problem with a tt, never come across it before and hope to never again. About a foot below the soil is solid rock however i've managed to get two rods in the ground at a couple of points using the kango hammer, the reading is still 320 ohms, any tips on what to do in this situation, is there another means of earthing that is easier to get in the ground with the rock the way it is? distributors earth is not an option as its a steel outbuilding remote from the supply head every tt i've done has been fine, some rocky ones but always able to get a good reading, sooooo frustrating

 

[andyb]

Does it have to be a tt system?
What is the earthing arrangement of the main supply, how far to your outbuilding and what have you run to it?

 

[monkeyelectric]

Does it have to be a tt system?
What is the earthing arrangement of the main supply, how far to your outbuilding and what have you run to it?

Tncs , its probably 50m and there is a building inbetween so this is coming off that which is connected to the main earth but there's no conductive parts in that one, but this whole building is steel so i don't want two different potentials

 

[andyb]

What size conductors and how many cores?

 

[monkeyelectric]

What size conductors and how many cores?

25mm 3 core swa to first then 16 mm 3 core to second, why's that?

 

[andyb]

The reason that you normally need a tt supply to outbuildings is that on any installation there is only one main earth terminal so any outbuildings with extraneous conductive parts will need an equipotential bonding conductor going back to the met and this can often mean a main bonding conductor of a larger size than the live conductors and it is easier to make it a tt system.

You have a 16mm 3 core going to your outbuilding, so as long as your main bonding conductors going to your met do not have a greater csa you can use the third core of your armoured as a combined cpc/main bonding conductor.

 

[Mac]

Get the metre drill bit out and pour loads of water over it

 

[monkeyelectric]

Get the metre drill bit out and pour loads of water over it

I got the plumber coming tomorrow to put a water supply straight to it, should sort it out

 

[tomo8163]

Hi guys got a small problem with a tt, never come across it before and hope to never again. About a foot below the soil is solid rock however i've managed to get two rods in the ground at a couple of points using the kango hammer, the reading is still 320 ohms, any tips on what to do in this situation, is there another means of earthing that is easier to get in the ground with the rock the way it is? distributors earth is not an option as its a steel outbuilding remote from the supply head every tt i've done has been fine, some rocky ones but always able to get a good reading, sooooo frustrating

hi there , the first question i would ask is, when you put the first earth rod in what reading did you get. when installing the secondary rod in did the reading go down, if so carry on putting more rods in until less than 200 ohms. if this dont work , maybe you might be better putting an earth plate in instead as not like a rod where you aim for depth, a plate will spread accross the ground instead. good luck

 

[RogertheBodger]

Take an Ra reading off the metal frame of the building. If it's got good foundations - might just do.

 

[somersetsparks]

^^^ second the above!

 

[somersetsparks]

On second thoughts though, is it not possible to use the combined csa of you armour and 3rd core as a bonding earthing conductor? thus continuing the PME, I don't like the sound of your soil conditions and would not personally leave it as a TT with those readings! Look at it now its wet! what will it be like in next summers inevitable 'heatwave'?

 

[rich.250]

Tncs, but is it PME???

 

[Engineer54]

Tncs, but is it PME???

Here come the scaremongers again!!! :angel_smile:

 

[DurhamSparky]

what the hell does that mean...

""Tncs, but is it PME???""

same bloody thing with a different name!