TT: A bit of guidance please

extec said:

This is not my thread as noted in another post my only question on this thread was how another member achieved less than 1 ohm on a TT install. I would suggest you read all of thread before making your comments and I should also be classified as a BELL END.

Click to expand...

I've corrected that for you!

No need to throw your teddies out of your pram

Extec chill out mate, there is no place for insulting regular members and getting personal.
We are constantly told by Admin to be nice to new members, but that can be extremely hard when you are throwing insults at everyone so enough is enough now.

trev said:

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.

Click to expand...

Thanks, I have no idea what the ground is like, but there is only one rod or one point should I say, how deep it is I don't know. As for connecting them, would you go from rod to rod then back to a central point, or bring them all back up into a terminal? Obviously to help bring the figure down using bigger cable would be better would it not?

davesparks said:

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.

Click to expand...

I can easily get one at the back of the double garage, one at the front and one at the side if needed.

extec said:

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

Click to expand...

True, but no idea what its like at present.

extec said:

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

Click to expand...

Its an end terrace with loads of space around it, so might not have too much of a problem.

davesparks said:

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

Click to expand...

Im going to ring WPD on Monday to establish what options are available. I did look at the pole out the front and its just got the cables going up to the top, I then walked down the street quite a way, probably 10 poles and none of them had any form of conductor going from the top to the ground at any point, not sure if this is relevant as I don't know how its done, but it didn't look like it was earthed anywhere nearby.

davesparks said:

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.

Click to expand...

Ill enquire on Monday, it would make my life easier if I didn't have to have a go with the rods. But equally I would very much like to have a crack at it as I have never done anything with a TT system before and it would be good experience.

To be fair, if someone said a 6mm earthing conductor in a TT install was too small, then went on to ask if a 300mA upfront RCD was required, then, surely they are not competent to do this work.

Click to expand...

That depends on what sort of Ra value they have achieved, it may well be inappropriate with a sub 1 ohm Ra. Like wise with the upfront 300mA or even a 100mA RCD, if this was an S type RCD it would make perfect sense....

Those that are not particularly competent would be those taking guidance from BS7671, like a paint by numbers exercise, because there is very little to no guidance in that publication, and what is there is there is being wrongly interpreted by those that can't think for themselves or outside of the box....

extec said:

In all respect I have never advocated in any of my posts that I believe a 200 ohm Ra is acceptable I always try and get the lowest possible value in the circumstances I am confronted with.

I showed an interest in a post which another member posted about achieving an Ra of less than 1 ohm and was advised by another two members that I shouldn't be installing TT systems. It happens all to often on this forum when some members post a question that certain members think they have a right to try and belittle and make the posting member feel they are not competent or worthy to be on the forum.

Click to expand...

I'm many tings matey, but one thing i'm not when it comes to electrical installations ...particually TT systems and that's a ''Bell End''!! I can also assure you, neither is Tony or Davesparks. I can't however say the same thing about the name caller!!

Now go back and read your posts on this thread again and tell us that you didn't mean that numpty 200 ohm Ra that BS 7671 mentions. Again i advise you to go back and read the advise given to UKsparks in this thread you may well learn something about how to properly create/install a TT system including suitable means of protection for TT systems that you can take to your next TT installation....

On page 24 of GN8 I see there's a table about the type of soil and resistivity which I will look at, just saying, I don't need a response to this.

Looking on page 28, Table 2.3, it looks at suitable materials for linking the rods together. Does anyone know where I would find the recommended CSA of the cable linking them or would you just use the same as the main conductor going back to the MET?

alanl said:

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!)

Click to expand...

Shut up will you.

alanl said:

To be fair, if someone said a 6mm earthing conductor in a TT install was too small, then went on to ask if a 300mA upfront RCD was required, then, surely they are not competent to do this work.
It is not that they are 'not worthy', but really, why try to make yourself look a fool, when you've got a green book in front of you to answer anything you don't quite know about?
It is in BS7671, and these facts should be pretty much known off by heart for such basic queries. If someone hasnt done a TT before, then maybe they should read up about it, learn a little more, then ask further queries once they have gained this knowledge.

However, such basic questions should be known by anyone calling themselves an electrician.
This shows how low the Industry standards are now, that someone is 'allowed' by their Governing Body to do such work, and the Customer is reassured that the Contractor is assessed, and passed to do such work, is, frankly, laughable, when it is clear they are not competent.

Click to expand...

The 6mm conductor, I am not saying this has never worked and doesn't provide an adequate connection etc, what I was suggesting is that it is less than the minimum CSA permitted by BS7671, see table 54.7 on page 162 of the BGB. It clearly states that the if the CSA of the line conductor is between 16mm and 35mm the CSA of the earthing conductor needs to be 16mm which is why I said it's too small as the CSA of the line conductor is 25mm ok.

The point of the 300mA RCD upfront, I said I was under the impression it was required, and I made it very clear I had not done a TT instal before and was after some guidance. So get down of your horse and stop being rude.

Also if you install an S-Type RCD you will not be fulfilling any requirements for additional protection. Additional protection is afforded by an RCD with a rated residual current of not more than 30mA and must disconnect within 40mS at 5xRated residual current. An S-Type RCD will not comply, see 531.2.1

On the other hand though, i think you would be a fool not providing an upfront S-type RCD device. it may not comply as additional protection, but will back up a failed downstream 30mA RCD. The reason I said can I put a 300mA there instead, is because neither a 100mA not a 300mA will save your life in terms of a fault and cutting out before you get belted, but both will meet the requirements of 532.1 for protection against the risk of fire.

So we have established that the upfront RCD is to be put there for protection against fire in the event of a fault, I and others have agreed this, so why are you taking the pee out of me for saying 300mA?? At least it wont trip out on a 5x fault on the board. Ok you could go for a S-type, but there's nothing wrong with a 300mA RCD upfront.

alanl said:

The main points are not aimed at you, - you said:
"It happens all to often on this forum when some members post a question that certain members think they have a right to try and belittle and make the posting member feel they are not competent or worthy to be on the forum"

Really, such queries should be told that they are not competent. Would they say to the Customer "Well, I havent done this before, and dont really know much about it, so I'll take a guess, then get the answer on the internet"

If you want to promote a quality trade, which adheres to standards, then surely such people should be told to learn more before they practice their trade on a customer?

Click to expand...

I'm not taking a guess at it at all, I am looking into it and reading the relevant books, IE. BS7671 and GN8 etc to see what I need, I will then call someone who has kindly offered their advice and discuss it with them, and when I am happy with what needs to be done I will then go back to the customer and say yes or no.

You are trying to make out that I am a novice and don't know what I'm doing and out my depth.

GMES said:

Extec chill out mate, there is no place for insulting regular members and getting personal.
We are constantly told by Admin to be nice to new members, but that can be extremely hard when you are throwing insults at everyone so enough is enough now.

Click to expand...

Well said, some people on here can be quite rude. There's one thing making a cheeky comment, but then there's people who are just rude and out for the kill.

extec said:

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.

Click to expand...

I think you need to prove yourself first before making a comment like that, and a post count of 18 doesn't exactly qualify.

just 1 point UK. the s-type RCD fitted to a TT system is not for additional protection. it is to provide ADS when the Ra ( Ze ) is too high.

telectrix said:

just 1 point UK. the s-type RCD fitted to a TT system is not for additional protection. it is to provide ADS when the Ra ( Ze ) is too high.

Click to expand...

Yes it would have to be less 30mA to be classed as additional protection, i was suggesting for ADS in the event of a fault.

Call me a bell end if you will but I think that Isolator in picture 7 might have an asbestos seal around the door.

Arghhh asbesos. don't panic, mr. mainwaring

eddieboy said:

Call me a bell end if you will but I think that Isolator in picture 7 might have an asbestos seal around the door.

Click to expand...

Yes you are a bell end as it didn't, but it did have asbestos flash pads in the fuse holders as did the unit above it.

uksparks said:

The 6mm conductor, I am not saying this has never worked and doesn't provide an adequate connection etc, what I was suggesting is that it is less than the minimum CSA permitted by BS7671, see table 54.7 on page 162 of the BGB. It clearly states that the if the CSA of the line conductor is between 16mm and 35mm the CSA of the earthing conductor needs to be 16mm which is why I said it's too small as the CSA of the line conductor is 25mm ok.

Click to expand...

A 2.5mm earth conductor may well be adequate, and I can say with some certainty that a 4mm earth conductor is adequate for your install.

Please, stop making statements that are clearly wrong - it may not be obvious to you, but it is wrong, and a 4mm earthing conductor WILL comply with current Regs., so long as it is not buried.

Engineer54 said:

I'm many tings matey, but one thing i'm not when it comes to electrical installations ...particually TT systems and that's a ''Bell End''!! I can also assure you, neither is Tony or Davesparks. I can't however say the same thing about the name caller!!

Now go back and read your posts on this thread again and tell us that you didn't mean that numpty 200 ohm Ra that BS 7671 mentions. Again i advise you to go back and read the advise given to UKsparks in this thread you may well learn something about how to properly create/install a TT system including suitable means of protection for TT systems that you can take to your next TT installation....

Click to expand...

First off I am not your matey and wouldn't want to be I based my opinion of you and the others mentioned not only after your comments to my post but on others I have read on this forum over the past 6 months.

I have read my posts made in this thread and still claim I have never said 200 ohms is an acceptable value for any TT installation if you want to use my reference to BS 7671 to try and justify your behaviour towards me then why don't you just refer to 1667 ohms also mentioned in BS 7671 which in theory is the maximum.

If you think any customers are willing to pay an electrician to mess around trying to achieve an Ra to gain ZS values which may never be achievable you are mistaken not in my part of the world where TT is the dominant method. If you have a two up two down mid terraced property supplied by overhead no PME with a tarmac pavement at the front and a 6 inch concreted yard at the rear you are limited to where rods or other methods can be used you do your best to achieve the lowest Ra you can in a timely fashion.

uksparks said:

I think you need to prove yourself first before making a comment like that, and a post count of 18 doesn't exactly qualify.

Click to expand...

I don't need to prove myself to anyone on here where as with the comments you have made with regards to your knowledge of TT it is you who should avoid installing anything to do with TT.

you need some of these.



but i don't know if they're big enough for your gob.:nopity:

alanl said:

A 2.5mm earth conductor may well be adequate, and I can say with some certainty that a 4mm earth conductor is adequate for your install.

Please, stop making statements that are clearly wrong - it may not be obvious to you, but it is wrong, and a 4mm earthing conductor WILL comply with current Regs., so long as it is not buried.

Click to expand...

You fit a 4mm earth and then show me how it complies with a 25mm line conductor and without using an adiabatic equation then.

telectrix said:

you need some of these.

View attachment 26626

but i don't know if they're big enough for your gob.:nopity:

Click to expand...

Maybe but the truth is even harder to swallow eh UKSparks.

Ok, ok, lets all go for a pint?

Boydy

extec said:

Maybe but the truth is even harder to swallow eh UKSparks.

Click to expand...

Show me how it complies then... Come on, put your money where your mouth is...

uksparks said:

You fit a 4mm earth and then show me how it complies with a 25mm line conductor and without using an adiabatic equation then.

Click to expand...

Why would you not use the adiabatic equation? The whole point of its existence is to calculate the size of an earthing conductor!

Off the top of my head I think the minimum for a TT system is limited by the minimum size of the main bonding.

Which raises the next question of what size main bonds you were planning on installing? (It's not the same as a TN system)

uksparks said:

Show me how it complies then... Come on, put your money where your mouth is...

Click to expand...

Seriously? The absoloute minimum size for an earthing conductor is 2.5mm if provided with mechanical protection.

uksparks said:

Show me how it complies then... Come on, put your money where your mouth is...

Click to expand...

Why don't you get your BGB out and read it you can read can't you? As AlanL has said 2.5 is suffice for a TT install provided its not buried if it is then it needs to be protect from corrosion and mechanical damage.

Is it Friday.?

I'll look further in to this, but regardless IMHO a 2.5mm main earthing conductor just doesn't sound right, if it is or not is a different issue, I'll be putting a 16mm in.

bonding conductors are 10mm by the way.