TT: A bit of guidance please

[telectrix]

Arghhh asbesos. don't panic, mr. mainwaring

 

[uksparks]

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

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.

 

[alanl]

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.

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.

 

[extec]

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....

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.

 

[extec]

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

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.

 

[telectrix]

you need some of these.



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

 

[uksparks]

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.

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

 

[extec]

you need some of these.

View attachment 26626

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

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

 

[guest119]

Ok, ok, lets all go for a pint?

Boydy

 

[uksparks]

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

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

 

[davesparks]

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

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)

 

[davesparks]

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

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

 

[extec]

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

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.

 

[7029 dave]

Is it Friday.?

 

[uksparks]

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.

 

[uksparks]

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

2.m sounds ridiculous but I'm sure you are right. Im just reading a section on it now.

I think I could be cut a bit of slack as I did openly confess at the start I hadn't done anything with TT.

 

[yellowvanman]

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.

When sizing earthing conductors you should be reading 542.3 and Table 54.1, where it states that with adequate mechanical protection the earthing conductor can be a small as 2.5mm. If this was the case the bonding conductor must be at least 6mm (544.1.1).

 

[uksparks]

Ok so section 542.3.1 table 54.1 states 2.5mm where burried and where mechanical protection exists.

I feel you have led me on slightly saying 2.5mm is the right way forward, but having read it I will eat pie or whatever the saying is and say I was wrong, but equally, it does say 16mm if not protected which it won't be, so I will still go ahead with the 16mm anyway, not only this, its only going to go towards lowering the resistance of the earth path, ok on marginal, but it all helps.

 

[alanl]

You are going to bury a 16mm cable unprotected?
Why not just run some conduit in?
The cost would be £5 or less, you will have to dig a trench anyway.
The cable is then fully protected, and you can use a smaller cable.
Burying an earth conductor unprotected is just daft wjhatever its size.

 

[uksparks]

No im not going to bury it... The existing one is right next to the wall, so no need, if I put another in, ill do it at the front of the property, ok I may need to put some conduit it round it there.

Ill still use 16mm regardless of what it says in the regs, theres not a chance I am going to run a length of 2.5mm.