Caravan hook up

Good afternoon, thank you for everyone's posts. I really do understand this but caravans on sites hook ups are earth roded. But caravans are not from the hook up to the caravan. So for 100% protection caravans should have an earth rod fitted and connected to its chassis to make it safe at its parked postion in a field. Not just at the site hook up point

Nothing's ever 100% safe. With TT systems the RCD is the weak point - research has showed that something like 7% of installed RCDs won't trip properly when required to (either not tripping at all, or too slowly). Earthing alone - without disconnection (at least with the sort of impedances a simple rod can offer) - doesn't provide foolproof safety.


Normally we say safety is adequate if two separate faults have to occur before danger arises - say a broken c.p.c. and an insulation failure, or (in the case of double insulated equipment) two separate insulation failures. Within an installation, a broken c.p.c. doesn't of itself give rise to danger - as long as there isn't also an insulation failure - the system is still unable to give anyone a lethal shock. On that score the approach for caravans is the same as for anything else - unless there's an expectation of high protective conductor currents a single c.p.c. or means of earthing is deemed adequate.


In fact not all caravan hook-up points have their own earth electrode (rod) - it's commonly done that way as that allows PME earthing to be used for the distribution cables and so avoids the complexity, cost and possibly reliability issues that can go with having multiple tiers of RCDs that would be needed for TT distribution. But where the distribution system is TT anyway (e.g. because it's fed from an Agricultural site or difficulties keeping earthing systems separate - e.g. where metallic piped services are used for static vans) then the hookup points can use the installation's earth facility with no extra rods are needed at each hookup. Very occasionally where it can be guaranteed that the earthing system is pure TN-S (say on a large site with its own transformer) caravans can be supplied from the main earthing system with no consumer's rods at all.


   - Andy.

Hardly practical.

Good afternoon, thank you for everyone's posts. I really do understand this but caravans on sites hook ups are earth roded. But caravans are not from the hook up to the caravan. So for 100% protection caravans should have an earth rod fitted and connected to its chassis to make it safe at its parked postion in a field. Not just at the site hook up point.

With respect, I think that Gino needs to learn a bit more about earthing.


I don't understand why SWA is proposed as a cable type - it does not appear to be exposed to any environmental hazards.


The problem with using the DNO's earth is, as Andy pointed out, that it is unlawful. It is unlawful because of the rare, but potentially lethal issue of a broken 'PEN' (= protective earth and neutral) conductor.


If it happened indoors, everything stops working, but the voltage of everything which is electrically connected can rise to mains voltage. Now if you touch your bright shiny kettle, you have the voltage across yourself to the kitchen floor; but you are wearing shoes and the kitchen floor also insulates you from the ground. If the same happens in a caravan, the whole thing including the chassis and other metal structural parts go up towards mains voltage. That may include a rail or handle by the door. This time, when you step out, your hand is at mains voltage and you may step onto wet ground so the resistance of the circuit can be much lower. If you aren't wearing shoes and the caravan site is bare (wet) ground, the problem may be a lot worse again.


So that's why you need a separate earthing system, which includes an earth rod.


HTH.

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.

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.

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

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.

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.