Caravan hook up

This is not a great question for a forum, you should really consult a professional who can provide the relevant calcs/testing and insurance.


Earthing is predominantly to provide an equipotential path that is common, as far as possible across the entire supply network so that faults that connect directly and indirectly to the physical earth will cause a large enough current to operate a protective device and disconnect the fault. Using an earth rod or not depends on the fault-loop impedance, as measured from a suitable test device (or calculated), the type of supply provided by the distributer and the types of protective device that are used. Because there are several variables, it is not a simple question of "yes use one" or "no, don't bother".

repost this in the wiring forum, and you will get a better informed set of answers, it is a perfectly sensible question but in the wrong place.

But please first find out how is your house earthed now -

TT

PME

TNS

?

you will need to know that as it affects the answer.

Also how is RCD protection afforded for the new circuit?


best regards Mike.

The complication with caravans is that the ESQCR prohibits the use of a PME earth connection for a caravan (or boat) - and since UK DNO's are liable to interconnect N and PE during network alterations the only safe policy is to assume that every DNO supplied earth terminal could be PME (unless there's been explicit assurance from the DNO otherwise). So generally the caravan socket will need to be connected to a TT system and separated from any DNO's earth facility. If the installation is already TT, then it's simple and no extra rod is required - it can just share the installation's.


Driving in a new rod will of course require a lot of care - not just from the risk of hitting exiting buried services (quite likely if you're next to a meter box and the supply is underground...) but really you should keep the rod well away from any underground metalwork that's connected to the PME system (old gas and water pipes, or lead sheathed cables for instance) otherwise you still have the same problem of the caravan's earthing system being taken to hazardous voltages should the supply CNE go open circuit. Ideally it should be subject to the same potential as the ground the caravan will be stood on, but that isn't necessarily straightforward when buried metalwork can have an influence over a much shorter distance than the length of a caravan.


Electric vehicle charge points have the same problem - and for them there is an option of using the PME earth together with a device that disconnects everything (L, N & PE) if an open-CNE is detected. They are a little controversial however (especially the single phase L-N voltage monitoring types) and as far as I know aren't recognised by the regulations for use with caravans.


   - Andy.

Andy thank you for taking your time. Wow so complex, funny as I was actually going to by a ev chrager pen device which monitors earth and will disconnect the supply. My thoughts were because my new hook up box will be connected next to the incomer box and all the wiring swa would be inside and very short that I could install without a rod as the risk of loose of earth would be very reduced as its so short, not like a caravan site where the hook up is in a field.

Is the caravan fixed or moveable. How far from the socket is it likely to be .



Gary

Good morning Gary Happy new year. The caravan actually is parked 3ft away from my proposed hook up. At the moment it's connected via the standard site type orange extension cable with a converter to allow me to plug in from my garage which is again 20 ft away all on tarmac.

Hi Gino.

It`s plugged in by a very common method then.

Not unusual. But, strictly speaking, unsuseable from a regs/safety point of view.

Whilst we do not have loads of dead bodies piling the streets from such acts it does have potential to become dangerous and that must be avoided.

That`s why you are asking and that`s why you`ve received such answers so far.

Bit confused, what I really wanted to know was if I fit my hook up on the wall directly next to the incomer main box, no expossed wiring at all can I connect to my home using its earth. If I was fitting a hook up say 20 ft away on a pole say like a caravan site I understand it would require the earth rood and for it to be TT. Ivor way if an standard caravan extension lead is used if there was a break from say earth rod /hook up box then the caravan would still be dangerous anyway. The only way is for a earth rod attached at the caravan chassis. Where ever the caravan is parked. In my instance the caravan is parked on my tarmac and the hook up box I want to fit will be on wall so the connection to the hook up would have its 1.5ft swa cable inside not expossed at all. Ivor way I fully understand the that caravan sites have an earth rod next to the hook up post, but the extension leads to the caravan are 10meters so unless the caravan its self has an earthrod then every caravan on any site is still expossed to this danger. Just because the hook up has a rod means that it's protected up to that point, but extending to caravan via extension lead means has stl its risk

The problem with TN-C-S supplies (which you have to assume you have unless your DNO guarantees otherwise) is that a rare but possible type of fault in the DNO network causes both the N and E to be severed (since at certain points in the network they are actually the same conductor). At this point all exposed conductive ( i.e. earthed metal) parts effectively become live. Inside a house this doesn't matter too much, since the bonding in place keeps everything at a similar potential. This means that e.g. both the metal case of an electric kettle and the metal sink tap are at a similar potential - both live. So if you touch both of them at the same time, you don't get a fatal electric shock.


Conversely there is isn't good bonding outside your house. So the earthed metal frame of the caravan reaches 230V potential while the ground and any nearby metalwork (e.g. gates) is still at 0V potential. So touching both at the same time could kill you.

as the risk of loose of earth would be very reduced as its so short

The issue isn't the risk of a break in the PE/c.p.c. between the intake and the caravan (that wouldn't immediately produce danger unless there was a simultanous L-PE fault in the caravan or there was high earth leakage equipment installed) - the worry is a break in the distribution network's combined neutral & earth (CNE or PEN) conductor. If that happens it would not only mean the loss of earth, but as there's almost certainly some loads connected, the severed neutral/CNE would be immediately pulled up to something approaching full mains voltage - and as the installation's earthing system is connected directly to the CNE under the PME system a single fault can cause all earthed metalwork to be very hazardous live - and for an indefinite period (i.e. until someone notices, calls the DNO and they send someone out in a van to fix it). That's not too bad inside a building where everything should be bonded together anyway, but outside where someone is likely to be in contact with the general mass of the earth, it's a different story.


That's why it's only an issue with PME (TN-C-S systems) - true TN-S systems don't have the same immediate hazard.


   - Andy.