TT rod installation guidance.

[Andy78]

Can anyone link me to any official guidance on the installation methods for earth rods in a domestic TT system.
Basically I am looking for something which would state that bashing a single skinny rod into the ground under the floorboards in a domestic property is not a suitable method of installation.

Not having any luck with my own searches so far.

 

[Engineer54]

The reading is around 40 Ohms right now, but this area has a very high water table and is sodden right now. There is certainly evidence of rubble within the ground under the floor.

I'd avoid internal placement of earth rods etc, always better to be positioned outside property boundaries....

If rubble is a problem excavate say a half metre or so, and then drive your earth rod in. No matter what anyone tells otherwise, ''Never'' use the the non extendable thin 3/8'' short twigs they are the next best thing to bloody worthless as an earth electrode!!

If the area has a high water table and the soil type is good, then a very decent and stable Ra value can generally be obtained with a little effort and time put into the installation...

 

[Des 56]

You have probably taken this into account andy,still I will post for the benefit of a.n.other

I would not usually consider dropping in a rod internally,it may cause damp issues by piercing any damp proof membrane

 

[GEOFF S]

I probably should have mentioned that a valid TN-S connection has been disconnected in favour of this rod. I didn't mention this as it's part of a huge can of worms concerning a CU swap that I'm currently helping a customer with, and didn't want the thread to get bogged down in other stuff.

I was really just after any guidance on accepted standards of rod installation to add to my ammo box.

Too keep it simple. Firtsly we need stability, to know what a stable reading is you need to know the ground resistivity. Then we need to consider seasonal variation and to what depth these varaition take effect. Then we need to decide what level of Ra we require. So with in depth ground resisivity measuremnts we can map the ground at varying depths and area. Then armed with this knowledge we can aply a equation or use software to calculate approximately how many and and at what depth the rods need to be driven.

Second option is to just bang a coupled rod in and hope for the best.

Cheers

 

[Andy78]

Too keep it simple. Firtsly we need stability, to know what a stable reading is you need to know the ground resistivity. Then we need to consider seasonal variation and to what depth these varaition take effect. Then we need to decide what level of Ra we require. So with in depth ground resisivity measuremnts we can map the ground at varying depths and area. Then armed with this knowledge we can aply a equation or use software to calculate approximately how many and and at what depth the rods need to be driven.

Second option is to just bang a coupled rod in and hope for the best.

Cheers

Option 3 has been taken in this case. Bang an uncoupled rod in and hope for the best.

 

[Engineer54]

I probably should have mentioned that a valid TN-S connection has been disconnected in favour of this rod. I didn't mention this as it's part of a huge can of worms concerning a CU swap that I'm currently helping a customer with, and didn't want the thread to get bogged down in other stuff.

I was really just after any guidance on accepted standards of rod installation to add to my ammo box.

You don't need anymore ammo, you'd have to be a complete raving nutter to ditch a working and compiling TN-S earthing system with a sub 1 ohm Ze, for a TT system with an Ra of 40 ohms that's stability may or may not be in question!!!

 

[Andy78]

You don't need anymore ammo, you'd have to be a complete raving nutter to ditch a working and compiling TN-S earthing system with a sub 1 ohm Ze, for a TT system with an Ra of 40 ohms that's stability may or may not be in question!!!

I was going on the assumption that if someone was willing to do this in the first place they might need showing something a bit more than my say so due to possible differences in understanding.

 

[telectrix]

take a Ze from the original TN-S connection point, then ask the other contractor which is the better value, his 40 ohms or whatever the TN-S gives.

 

[Engineer54]

I was going on the assumption that if someone was willing to do this in the first place they might need showing something a bit more than my say so due to possible differences in understanding.

What like him being led off to the nuthouse by the men in white coats??