TT: A bit of guidance please

[extec]

3 8.3 0hms is a lot better than 200 BUT with a bit of effort you can get this to >1ohm

How much effort are you talking about? I would be interested in how you achieve less than 1 ohm on a TT

 

[uksparks]

I don't know what the Ra of the rod is on it's own as only did a Zs at the board, but would like to get it down under 1 if I could.

I could put additional rods in I guess and hook them all together.

 

[trev]

How much effort are you talking about? I would be interested in how you achieve less than 1 ohm on a TT

A lot depends on the type of soil you're going to whack into. You need the biggest, fattest rods (note, not rod) you need to couple them together and drive them deep.
If you can't do that you need to look at tapes and plates and multiple rods.
It's not hard mate.

 

[davesparks]

How much effort are you talking about? I would be interested in how you achieve less than 1 ohm on a TT

Depends on the soil conditions and available space.

I start with 2x 8' rods spaced at least 10' apart as a baseline for a small installation and take it from there.

 

[extec]

I could put additional rods in I guess and hook them all together.

That would depend on the type of ground you are driving them into.

 

[davesparks]

Depth gives stability, but the relationship between depth and the reduction in Ra values is not linear.
Initially the Ra will reduce dramatically for each foot deeper you go but you get to a point where you get no appreciable change for the increase in depth.

So you need multiple deep rods to get the values low

 

[extec]

Depends on the soil conditions and available space.

I start with 2x 8' rods spaced at least 10' apart as a baseline for a small installation and take it from there.

Difficult to achieve if the installations are on terraced properties without garden space.

 

[davesparks]

Difficult to achieve if the installations are on terraced properties without garden space.

One at the front of the house and one at the back.

But you don't find many terraced properties without gardens in country areas, they tend to only be in towns. And as we all know TT systems are normally a countryside thing.

All of the TT systems I have found anywhere near a town have had PME available and all you have to do is get some 10mm bonding installed and the DNO will connect PME FOC

 

[extec]

A lot depends on the type of soil you're going to whack into. You need the biggest, fattest rods (note, not rod) you need to couple them together and drive them deep.
If you can't do that you need to look at tapes and plates and multiple rods.
It's not hard mate.

Aye that's a lot more effort than some of the jobs are worth for me I thought you may have discovered some way of making the job a lot easier.

 

[davesparks]

Aye that's a lot more effort than some of the jobs are worth for me I thought you may have discovered some way of making the job a lot easier.

If you aren't going to do the job properly then don't do it at all!

 

[trev]

And as we all know TT systems are normally a countryside thing.

I disagree, we live near a busy road into a fairly large town. We're on a TT with a sub 1 ohm Ra

 

[yellowvanman]

With a low L-N value/High PSCC you could be in PME territory. Call the local DNO to check.

PSCC (L - N)
0.19 Ohms
1.3kA PFC

 

[extec]

If you aren't going to do the job properly then don't do it at all!

Ha ha you can't seem to help yourself can you the job is done properly within the guidance set out in BS 7671

 

[davesparks]

I disagree, we live near a busy road into a fairly large town. We're on a TT with a sub 1 ohm Ra

I did say normally in the countryside, not always.

Have you confirmed that PME is not available? I'm not suggesting that you should have it connected though, especially not with an Ra as good as that!

As I said earlier all of the TT installations I have come across around here within a reasonable distance of a town have had PME available. And since the connection by the DNO is free then I generally get it done.

 

[trev]

I did say normally in the countryside, not always.

Have you confirmed that PME is not available? I'm not suggesting that you should have it connected though, especially not with an Ra as good as that!

As I said earlier all of the TT installations I have come across around here within a reasonable distance of a town have had PME available. And since the connection by the DNO is free then I generally get it done.

If it was available I'd have it done in a heartbeat mate, I've checked though.

 

[Engineer54]

Aye that's a lot more effort than some of the jobs are worth for me I thought you may have discovered some way of making the job a lot easier.

Ha ha you can't seem to help yourself can you the job is done properly within the guidance set out in BS 7671

Any guidance given in BS7671 which relates to the numbty 200 ohm Ra values can be thrown straight into the nearest bin. At best it's referring to stability, and nothing beyond that. I take it from your posts above, that you'll also be using the equally useless 1.2m thin 3/8'' non-extendable twigs for your earth electrode installation, that basically can't ensure any stability to your ultra high Ra values too.... You'd do well to listen and take note of what has been stated above by those that Know what they are talking about!!


Do your customers a favour, ....Stay well away from TT installations!!!

 

[extec]

Any guidance given in BS7671 which relates to the numbty 200 ohm Ra values can be thrown straight into the nearest bin. At best it's referring to stability, and nothing beyond that. I take it from your posts above, that you'll also be using the equally useless 1.2m thin 3/8'' non-extendable twigs for your earth electrode installation, that basically can't ensure any stability to your ultra high Ra values too.... You'd do well to listen and take note of what has been stated above by those that Know what they are talking about!!


Do your customers a favour, ....Stay well away from TT installations!!!

Another Bell End you know nothing about me or my installations this forum has some well informed people and some which for some reason think they know everything about everything and about everyone. Thank you for your advice but I know what I am doing with a TT install and what is acceptable if you can't add anything constructive shut up.

 

[alanl]

This thread has shown that some supposedly 'competent' people are just not at all competent to install some very basic equipment in peoples houses (or anywhere else for that matter.)
6mm earth? 300mA RCD? Not quite sure about some things.
How about not sure about a lot of things?

How can anyone quote for such a job when they do not have the relevant knowledge to do it properly?
Of course, all is good, as the customers are protected as the person doing the work has been 'assessed' by their Governing Body. (laughs all the way to the bank!)

 

[Knobhead]

Extec

 

[extec]

Extec

And another BELL END once one comes out the others follow if you think this kind reply is what the forum is about why do you bother you sad individual. You have used this on a number of occasions to try and belittle members there is only two kinds of special idiot here and you are both of them.