caravan park tt system and earth rods

[mcmainelectric]

Hello everyone,
Have been inspecting caravans statics at a 200+site. The levels of ZE are 8+ ohms at the caravan hook up and it is on a TT system (the incomming mains) to 4 or 5 submain distribution points where there is a common earth rod and from there via swa using the cable core or armourmed as the cpc to the individual hook up points.
My question does each caravan need its own earth rod? or is using the collective one at the submain distribution point acceptable?
I feel the tt system is being turned into a poor tns, but i cant get any answers from the regs to help
regards

 

[richy3333]

I've read the thread with interest, particularly as I've just spent considerable time TT'ing static vans that were on TNCS system.

Caravan park systems manifest themselves in various guises with statics, mobile vans, tents etc. And then there are the outbuildings to be earthed

I'm surprised nobody has mentioned GN3 yet, which describes Eng54 and Wirepullers opinions on the different options (and gives diagrams). Both are equally valid and I guess it's horses for courses etc. Personally I prefer separate TT'ing for each static.

One other issue is this magical 200 ohms. The BGB/GN3 et al doesn't say that the Ra has to be below 200 ohms, it just states that over 200 ohms a system can be unstable. Ground conditions also play a huge role in TT'ing, particularly if the ground you have to use isn't great?

 

[Deleted member 9648]

I've read the thread with interest, particularly as I've just spent considerable time TT'ing static vans that were on TNCS system.

Caravan park systems manifest themselves in various guises with statics, mobile vans, tents etc. And then there are the outbuildings to be earthed

I'm surprised nobody has mentioned GN3 yet, which describes Eng54 and Wirepullers opinions on the different options (and gives diagrams). Both are equally valid and I guess it's horses for courses etc. Personally I prefer separate TT'ing for each static.

One other issue is this magical 200 ohms. The BGB/GN3 et al doesn't say that the Ra has to be below 200 ohms, it just states that over 200 ohms a system can be unstable. Ground conditions also play a huge role in TT'ing, particularly if the ground you have to use isn't great?

Yes,this was discussed on another thread....and as we know,if a 30ma RCD is in use a final Zs of 1667 ohms will still provide the required disconnection time,so in theory an Ra of 1667 - R1+R2 would be accaptable......(note I said 'in theory'!):earmuffs:

 

[GLENNSPARK]

I've read the thread with interest, particularly as I've just spent considerable time TT'ing static vans that were on TNCS system.

Caravan park systems manifest themselves in various guises with statics, mobile vans, tents etc. And then there are the outbuildings to be earthed

I'm surprised nobody has mentioned GN3 yet, which describes Eng54 and Wirepullers opinions on the different options (and gives diagrams). Both are equally valid and I guess it's horses for courses etc. Personally I prefer separate TT'ing for each static.

One other issue is this magical 200 ohms. The BGB/GN3 et al doesn't say that the Ra has to be below 200 ohms, it just states that over 200 ohms a system can be unstable. Ground conditions also play a huge role in TT'ing, particularly if the ground you have to use isn't great?

As i pointed out above....<200 ohms as long as you can guarantee stability..........

 

[Engineer54]

Yes,but not essential...and as far as a PIR goes the inspector needs to be very careful over introducing requirements which he percieves to be good practice...but is beyond the requirements of 7671. Whatever the inspector thinks his only duty is to code non compliance.
I think where I have taken issue with you before E54 is your complete dismissal..(in previous threads)...of single point TT earthing,regardless of the fact that such an arrangement properly installed complies with bs7671 and will provide a perfectly safe earthing system. I would agree that your advised earthing system makes a lot of sense...if the additional cost can be justified to the client.

I think we somehow got past the OPs PIRs, and on that score, your dead right. He just needs to go through his work methodically and noting down his considered discrepancies, and checking against actual Regs if they are indeed non- compliances or not before issuing his certs.

Yes, much of our disagreements have been about single point, and single rods as i remember. But i think this situation is quite different as the only earthing conductors, apart i think from one or two instances, are the SWA of the distribution cables!!

Though i do take issue that the current trend in the UK of using these short 3/8'' thin rods, can in anyway, shape, or form be considered able to provide a perfectly safe and therefore sound earthing system. Not when that top metre, will be doing little to nothing in the UK's adverse weather conditions, such as freezing temperatures and high temperatures where the soil just dries out. That really doesn't leave much of the rod left, to provide a safe earthing system.

I agree with you completly on the costs of providing a full blown TT system that will deliver the goods come what may!! lol!! Unlike you and the other self employed sparks here, where costs to the client via your quotes and estimates can mean the difference of getting the job/contract, i have no such concerns/worries on the projects i'm involved on. So i can at times go a little overboard on things! ...lol!!!

But we'll leave it there, as we have done in the past, and agree to disagree on certain aspects...

 

[topquark]

Yes,this was discussed on another thread....and as we know,if a 30ma RCD is in use a final Zs of 1667 ohms will still provide the required disconnection time,so in theory an Ra of 1667 - R1+R2 would be accaptable......(note I said 'in theory'!):earmuffs:

Until you start testing at 1x and it doesn't trip eh?

 

[Monkey]

Good morning boys, its a good subject this one,:6: having read all the posts here s one( if i can load it on the screen) is a picture from a site I tested the last electrician decided to cut off all the bajos that had been joined together thus removing the earth path of the ring yes PME site with plenty of earth rods so he got confused about earthing leaving swa cables unprotected (204 was replaced )

 

[Deleted member 9648]

Are you sure you have not introduced a PME earth by joining them up again?

 

[Monkey]

Hi wirepuller I have introduced back and stopped it at the point were the caravans join the supply!

 

[richy3333]

Monkey - can you clarify. Do you mean that the SWA supply is on the PME and each hook-up box is TT'd (that's what I think you are saying)?

 

[Monkey]

Hi richy3333

yes it is now

but before the swa had no earth parth

 

[Engineer54]

Hi wirepuller I have introduced back and stopped it at the point were the caravans join the supply!

Yep, ....All your doing there is, maintaining the continuity of the PME's SWA earthing system, your not incorporating any fly leads from those banjo link connections...

 

[richy3333]

Thanks for clarifying Monkey. Sounds good to me.

I label my Hook-up boxes with a warning about the earthing type, just in case some muppet 'looks at it' sometime in the future - can't say they weren't warned about what has happened!

 

[GLENNSPARK]

Fancy goin round croppin all the banjo`s??????????