Caravan hook up on side of the house

[CornishCrofter]

A friend of mine has a caravan she wants to use for commercial purposes next to the house and needs a caravan hookup. I wanted to talk through the installation with you guys please.

Before I go on, a bit of background about me. I have taken and passed the 16th Edition and Inspection and Test. I know we're onto the 17th Ed now but I do have electrical qualifications and am normally well disposed towards discussing issues like these.

The property is served by an old Wylex BS1363 Consumer Unit that is very lightly used. From what I can establish there seems to be only one or perhaps 2 ring mains and a lighting circuit. Cooker, water heating, shower etc is all gas/combi boiler. So, with diversity there is certainly plenty of capacity for it.

We don't know what the earthing arrangements are for the supply, except that it is not a TT earthing system. We know if it is a PME then an earth rod will be needed for that circuit or the supply to the caravan. There is a chance it could be TNS but I'm thinking I will have to install a TT earth for that circuit only.

Now, the caravan hookup point comes with its own RCBO so I am told. Hence I was looking to use a suitable way from the Consumer Unit, protected by a 16 Amp mini switch and run a 2.5mm T and E cable from the CU along the inside of the house in surface mounted trunking to afford suitable protection, and through the wall directly behind and into the hookup. The 16mm earth to the copper rod would be connected to the hookup.

My only area of confusion is at what point in the new circuit to I split off the earths. One will be connected to the earthing system in the house whereas the other will be connected to the TT system. I am aware that the two need to be electrically isolated.

My take would be that the electrical isolation would need to be at the point where is the RCD or RCBO is. That way the part of the circuit that is not isolated when this trips is not served by a TT earth with a high Earth Loop Impedance. Hence the cable in the house would be served by the earthing system for the main supply and the hook up point the other side of the RCD would be served via the TT earth.

Would this be correct?

BTW, I am told that the 17th Edition regs doesn't actually cover a hookup at the side of the house, but only caravan sites, so my chat with the IET today centred around I think the EW regs.

The LABC would be notified of this.

Thanks

 

[ericmark]

It is an interesting problem as with a caravan site the caravan has to be a fixed distance from the building due to fire regulations so the proximity of extraneous-conductive-parts does not present a problem.

However with a caravan parked at the side of a house often the extraneous-conductive-parts of the house can be touched at the same time as the metalwork of the caravan and to have two different earthing systems would present a danger.

In the same way two connected houses or houses that close that extraneous-conductive-parts from each house could be touched at the same time could present a danger which is why it is the DNO who decide what system of earthing should be used not the electrician working on the house.

This leaves us with a problem in some cases when wanting to use a TT system. What we have to remember it is not a caravan / camping park so the section 708 does not apply.

ESQCR states:-
PART II
PROTECTION AND EARTHING
Protective multiple earthing 9
(4) The distributor shall not connect his combined neutral and protective conductor to any metalwork in a caravan or boat.

But your not the distributor.

The only safe way is with an isolation transformer but I tried to get a cheap one for my sons boat and not such beast they are expensive lumps.

So I would say all you can do is use your electrical knowledge and use some common sense. How far away is "Next to" and is that far enough to ensure the voltage gradient under fault conditions is enough to be safe?

The real answer is the minimum of 6 meters see this PDF will likely mean both voltage gradient and fire regulations are satisfied. However if closer then 6 meters you can't use the caravan in that location.

I would earth the SWA at the house and use a stuffing gland at the caravan hook point. If less than 6 meters I would not use a TT supply and I would state in paperwork it was an outdoor supply for lawn mowers and the like and should not be used for a caravan even though I know it will be.

If the LABC know their stuff they will not allow you to provide a caravan supply. However this again is a problem as a caravan is not a building so it's only the socket supplied from house that they inspect not the caravan.

It has to be remembered you can't have a law or rule to cover when laws or rules are broken. So if less than 6 meters between house and caravan the whole lot is breaking the rules so all you can do is use common sense.

 

[CornishCrofter]

Thanks for that.

As you say, there's no easy way around that one. This is a favour for a friend really. She got someone to quote to do this work and he was going to use the SWA cable around the outside of the house.

My initial thinking was that I could route a cable properly protected and rated inside, and avoid the need to use SWA. The only reason one would need SWA would be for exterior protection.

Initially I was thinking of connecting the earth to the whole supply to a TT spike but on thinking about it I realised that in the event of a short to earth, the trip would go in the hookup and isolate the caraven but there would still be a life earth inside the house!

Your approach of earthing the supply cable to the CU and not via the hookup to a TT system would at least solve this.

That does leave the caravan hookup unearthed though, unless we go to the extend of actually grounding the caravan chassis to earth as well as putting in the TT system

 

[ericmark]

You have not answered the main question. Is the caravan more than 6 meters from the house?

If it's over 6 meters no question I would use TT supply.

If under 6 meters then you need to look at what can be touched outside the house. Metal soil pipes, gas pipes etc. If under 6 meters it's breaking the rules anyway so you have to forget the rule book and decide which is safest method.

What I worry about is the lawn mower. If the lawn mower is class II then no problem but if class I then you can get two earth systems very close.

My father-in-laws motor caravan was 3 foot from house and we used the TN-C-S supply that was safest method. But it was only stored not used in that position.

 

[JohnD]

Eric, your pdf relates to caravan parks.

A caravan that's put next to the owner's house for the winter is not in a caravan park.

The OP's "commercial purposes" is very vague, but doesn't seem to be in a caravan park either.

 

[Lectrician]

Best thing to do would be to confirm 100% what the current earthing system is, and then let the arguments commence if it turns out to be PME.

 

[CornishCrofter]

Caravan is less than 6m from the house. Looking at extraneous conductive parts on the outside of the house, there are none at ground level.

Guttering is UPVC as are the windows bar one which is wood. The front door is close but that faces away from the caravan.

The closest think to the caravan made out of metal is the satellite dish and that is from memory near the eaves of the house.

Thanks for all the replies. It seems that a sensible well thought out approach is needed as this doesn't fit in any rule book, as is being said.

 

[ericmark]

Personally I would not bother with a TT supply. I agree that in the UK the ESQCR prohibit the use of a TN-C-S system for the supply to a caravan. And the ESQCR does not say caravan parks it just says caravans. But there is a big difference between the DNO putting a supply into a caravan and taking a supply from the house.

My father-in-law had a socket to supply out door items and when not used for lawn mower the motor caravan was plugged in to it. Since you can provide a socket for other items without it being TT then I would just be careful not in the paperwork to refer to it as a caravan supply.