testing static caravan installations

[Dic Penderyn]

Similar to what Malcom pointed out, Earth is paramount, get yourself a long lead and test the chassis remembering the touch voltage (50V).

In most cases the Zs and Zdc readings at hook-ups and within caravans can be extremley high. If the Park manager is reluctant to spend on upgrading earthing at hook-up etc....just write an addtional report highlighting the dangers and send it the owner along with EICR.

Solution:

It would mean re-glanding at a number of hook-ups if it's a TNS system with SWA or running a separate earth cable. In some cases it might be re-newing a roofer bolt and nut.

If you are unable upgrade earth, would it be worth installing a rod to get the reading down in spite of the regs stipulating that 2 x earth systems shouldn't be mixed?

 

[Engineer54]

You can incorporate a rod on either a TN-S or TNC-S (PME)!! You can't mix the TN earthing systems, past the the service cut-out, but a lot of the DNO's local network distribution cables carry both. Mainly where a cable string is in the process of being PME'd, usually because some sections of the cable lead sheathing has broken down etc...

 

[Dic Penderyn]

Hi Engineer!

I have read a few of your threads regarding earthing, and there seems to be mixed opinions with mixing systems after cut-out i.e. TT and TNS or TNCS. Nevertheless very interesting!


The caravan park which I have done work for has had problems with HIGH Zdb. It's a TNS system and the easy answer would be to re-gland at each hook-up or install an additional earth cable to reduce the ELI. However, the park manager is reluctant to spend on this, so there's no easy answer?

Could it be possible to change the system to a TT at the hook-up?


Cheers:thinking:

 

[SimpleSimon]

What about giving each pitch its own rod?
54 is right, doing this isnt mixing two earthing systems, your just incorporating your rod into your TN-S. There's nothing wrong with this.
Sent from my GT-I9100 using Tapatalk

 

[SimpleSimon]

In fact, see reg. 708.553.1.14, thought id seen it somewhere.

Sent from my GT-I9100 using Tapatalk

 

[Engineer54]

Hi Engineer!

I have read a few of your threads regarding earthing, and there seems to be mixed opinions with mixing systems after cut-out i.e. TT and TNS or TNCS. Nevertheless very interesting!


The caravan park which I have done work for has had problems with HIGH Zdb. It's a TNS system and the easy answer would be to re-gland at each hook-up or install an additional earth cable to reduce the ELI. However, the park manager is reluctant to spend on this, so there's no easy answer?

Could it be possible to change the system to a TT at the hook-up?


Cheers:thinking:

If your having problems with Zdb, then someone hasn't designed the distribution layout very well. Probably from undersized cables running too far. The Park Manager, as well as the owner(s), have a duty to ''ensure that the electrical distribution system meets the appropriate safety regulations ...and meeting disconnection times is way up there among the most important of those!! Sounds as if your relying on RCD devices in this aspect, and they should only be seen as ''Additional Protection'' on a TN-S system....

I doubt very much if installing rods are going to improve your ELI results very much, if at all. Yes you could change the system from TN-S to TT, but would you really want too??
Nothing stopping you using a rod at each hook up point, can't be any worse than an all TT earthing system and RCD device!! ...lol!!

 

[wildgoose]

Using TT rods to supplement the existing TNS earthing system surely has to be a good idea? Unfortunately the 2 caravan park owners that I've dealt with, would not accept upgrading their main supply cables or even a dig-up to run a supplementary earth line! In the end, individual TT rods at the side of every post did the job and this was at least fully supported by the site owners.

Ironic that it's acceptable for an exclusive TT system to not meet the disconnection times but then it takes into the consideration the serious extra level of safety from the supporting RCD's!!

 

[Engineer54]

Using TT rods to supplement the existing TNS earthing system surely has to be a good idea? Unfortunately the 2 caravan park owners that I've dealt with, would not accept upgrading their main supply cables or even a dig-up to run a supplementary earth line! In the end, individual TT rods at the side of every post did the job and this was at least fully supported by the site owners.

Ironic that it's acceptable for an exclusive TT system to not meet the disconnection times but then it takes into the consideration the serious extra level of safety from the supporting RCD's!!

That's basically down to the low quality and low expectations of a UK TT system. You are then relying totally on a RCD device for your earth fault protection/disconnection times. Which is not really the best place to be, considering the they are not the most reliable form of protection device. You only have to check the threads on these forums to see that!!

 

[pap1986]

I've been testing caravans on a farm. Two sites of about 50 vans. Some of the alterations I have come accross will make you sick. I've seen 13amp sockets wired in 1.0mm T&E a 7KW shower with no earthing and on a D 63 amp MCB and a light wired in CAT5 but dont worry they doubled up the cores. The most common problem is the amount of convector heaters
on extension leads the put of a single socket, resulting in most sockets being compleatly burn out, but they will continue to use them anyway.

I was testeing each van as I would a house(full periodic test and inspect) and doing the supplys to the van on a seperate certificate. All the vans were TT but most of the rods had been cut off or riped out. because on farm, they have the attitude if something trips remove the earth and replace all fuses with nails.

 

[Deleted member 26818]

708.411.4 TNS or TT. TNCS prohibited by BRB and ESQCR. Statics are non permanent buildings and are normally found to have their wheels still fitted even though they might be up on brick pillars, or the like. The owners often put a small wooden 'pelmet' around them to hide this.

Here's a Regulation from BS 7430. I'd draw your attention to the note at the end of the Regulation.
21.10 Mobile (touring) caravans and caravan
parks
The electrical protection of persons and livestock
using, or in contact with, a caravan has to be reliable
since a fault to earth of equipment within that
caravan can result in its frame rising to a dangerous
voltage above that of the ground on which it is sited.
Any person then touching any metalwork of the
caravan while standing outside is open to the risk of
electric shock.
Because of the special hazards associated with
caravans, the current Electricity Supply
Regulations do not permit the use of PME systems
for their supply.
Permanent buildings on a caravan park may be
treated as if they are ordinary premises and may be
supplied and protected by generally adopted
methods. In such cases the main earthing terminal
of an installation which is part of a TN-C-S system
may be used.
NOTE Residential caravans which are not normally intended to
be moved from a caravan park are regarded as permanent
buildings.

 

[richy3333]

Hi Spin.
Referring to the BGB S708 deals with electrical installations in caravan/camping Parks and S721 electrical installations in caravans and motor homes.

708.411.4 prohibits the connection of PME earthing to any metalwork in a leisure accommodation vehicle (including a caravan). Part 2 definitions describes a leisure accommodation vehicle as 'unit of living accommodation for temporary or seasonal occupation which may meet the requirements for construction and use of road vehicles'.

In the context of my earlier comments, which were probably not fully clarified I was alluding to a specific situation. The site owner does not consider the 'van' as permanent and lease contracts place a life span of 10 years on each unit. The occupancy is only temporary and is definitely only seasonal (March to October). Leases are renewed annually and if the owners do not want the pitch any longer they are responsible for removing their van - be that towing or crane lifting onto a flat bed lorry etc.

I can't reference BS7430 myself - unable to find a copy of it on the web and BSI want approx £200 for a copy! However the use of the word 'residential' in the note you mention is suggestive of permanent (didn't want to use that word but couldn't think of a better one) occupation and thus not temporary or seasonal.

One thing all this highlights to me is that the whole area is somewhat of a minefield and that one needs to get their context correct before proceeding with any electrical work as we have, caravans, leisure accommodation vehicles, residential caravans, residential park homes, mobile homes, transportable units and motor caravans to name but a few!

 

[Deleted member 26818]

It's not really a minefield, just very open to interpretation.
Many 'Caravans' are not capable of being towed behind a vehicle on the highways.
They have the wheels and running lights etc. just to comply with planing Regulations and Bylaws.
If I don't consider that the Caravan is capable of being towed on the highway, or in some cases, if there is no intention of ever towing the caravan, I will consider it as being permanent, irrespective of whether occupancy is seasonal.
Other opinions will differ.
Of course, if the Ze/Zs is too high, the question can become acadimical, as it may need to be TT'd in order to meet disconnection times.
At the end of the day, you're the inspector, it's your call.