PME earthing to a group of static caravans TT earth required?

In terms of the regs, maybe not, as static caravans are not explicitly mentioned. But you should ask is the risk the same - the problem with a PME system generally, and this is true for car chargers garden sheds and containers / portakabins, and barns in farm yards, that the PME ' earth'  is not quite at the same potential as the true terra- firma earth, and this can lead to discomfort tingles if the user has simultaneous good contact to bare earth, or something at bare earth potential, and something at the PME earth potential . Also under network fault conditions, the PME 'earth' can be at a significant fraction of the phase voltage, but indoors in the dry, who cares, as it is all bonded, and goes to the same high voltage, and no shock is felt.


So we should ask is this a problem for this case - can someone touch the PME earth on the caravan door frame perhaps, while also touching the true ground with their feet ?

Professionally, I'd not worry about things that are seldom touched and normally painted, such as a lamp post on PME, nor would I worry if the ground path is poor, as it is indoors on a wooden floor, or even for an occasionally used storage container used by booted workmen on a thick layer of free-draining gravel. I would worry about the same container in frequent use in a farm yard sitting in lots of mud and conductive animal residue, or where children in bare feet, or expensive livestock, may get near it.

The regs require us to worry about metal cars on EV chargers outdoors, and caravans. In other cases, like this, you need to decide how much of a risk this is. For comparison, the static vans round here, (mother in law has one) are all installed as TT, as they have little flower beds beside  and are entered  via metal steps that are concreted to the true ground, so the credible risk is simultaneous contact with the hand rail of the steps and the front door, and I'd tend to suggest what you have in mind may be similar.

Thanks Mike, pretty much what I am thinking. My leanings are that the risks are broadly similar to caravans, so that a TT earth would be prudent. I am looking for others views to make sure that I am not being over zealous...

In terms of the regs, maybe not, as static caravans are not explicitly mentioned.

There have been some changes in the 18th and "residential park homes" do now get a mention in section 708. The BS 7671 prohibition on PME now seems to extends to all socket outlets on the park's installation -  whether they're supplying a caravan (tourer) or a residential park home (static). That wouldn't apply in the OP's case where the static is hard-wired though.


Interestingly the requirement for 30mA RCD protection also extends now to fixed connections to residential park homes - so things are definitely tending away from treating statics 'just like any other building'.


  - Andy.

The SWA armour can stay as the PME earth, so that if anyone digs it up, it trips ADS with a convincing bang, The caravans unless very old, will have RCD protection on the incomer any way, so the only need is to insulate the PME earth at the van end, and add a local earth, which assuming you can get a rod in, should be reasonably straight forward. Could even be done in an adaptable box on the outside of the van, perhaps underneath,  if there is no appetite to disturb the internal decor.

For the opposite slant, on just how bad it can actually get, try reading this  old thread .

I lived in a static for many years and from memory I'm pretty sure I had TN-S earthing.

If only....life was that simple. I have asked DNO about TNS and they say no. Its really rocky too which doesn't help TT earthing

Immediate kneejerk response is ... definitely needs an earth rod per caravan (metal frame WILL be introducing true earth)... and the requirements for TT seem less onerous in this example?

Well, that's sorted then, make sure you are wearing big boots, (and rubber gloves of course)


Regards, UKPN