BS7671:2018 SECTION 708

Have had plumber under the lodge Chris clearing a pipe blockage.

Are you now of the opinion that the Lodges would then be better off with separate Earth Electrodes and separate from the DNO PME Earth.

AJJewsbury said:

Although, other than the chassis, we have those same risks on ordinary (PME) houses....

How is the chassis different to metal pipes running under the PME house, and even outside it?

Phil,

BS 7671 has, for some time, recommended that an additional earth electrode is provided for installations connected to PME (not separate).

But I think the pictures here clearly illustrate the difference - in the park home here, metalwork connecting to chassis links to ground, quite clearly ... and when completed with cladding etc., difficult to access the metalwork.  Very different to caravan on tyres, possibly also with plastic pads under the lowerable stabilisers ... and possibly in a muddy field ... with parts of the metal trailer chassis still accessible despite the fact that construction of caravans has, too, changed over the years.

Electric vehicles are more like caravans, as they are on rubber tyres completely, totally separated from local ground.

Afraid that I am reluctant to express an opinion. However, I think that we have distinguished between a situation where the chassis is inaccessible from one where it is accessible.

Any danger to e.g. a plumber could be eliminated by isolating the supply during maintenance underneath the lodge. However, my point was that if the void is being used for storage, particularly of a large metal object, the resident could be in contact with the chassis on a reasonably regular basis.

Agreed ... but  in contact with the chassis.but with what area, and what exactly to form a circuit to cause a hazardous voltage or current?

You need to be careful about these definitions of park homes etc.

you are straying into the the realms of the Local Authorities Planning Departments rather than their Building Control Departments.

Some years ago one of my customers had temporary Planning Permission for five years to site a mobile home on a farm for a groom to live in look after horses being imported from Mainland Europe.

Around twenty years later it was still there and they replaced it with a timber cabin, someone reported this to the Planning Department at the Local Authority, there then followed a couple of years of formal discussions about wheels and what the legal definitions are of moveable and transportable are. One of the things discussed was that it actually uses the original electrical, water and sewage connections with the owner pointing out that although it looks different physically nothing much actually changed on site.

The cabin is still there, the planners put some restrictions on it and both they and the owner spent a few thousand pounds on having the discussions about it, employing professionals to represent them.

Regards the park home under discussion, if you own it converting the installation earthing to TT is not complicated or expensive, but I will suggest that you really need 10 metres separation between this homes electrical installation and the other installations.

It will get more interesting if people are or will be charging electric vehicles on site.

To be honest the park home chassis is less of a risk than my outside water tap which is plumbed with copper pipe.

It looks like a relatively new site. If the DNO distribution system is new, with modern joint kits, it is almost impossible to lose the neutral. In any event, if there was to be an injury, then someone should sue the ass off the DNO! 
An approach to HSE in this part of the world confirmed that not one single incident has been investigated in the last 20 years (as long as the officer responding to my query was in post). That is not to say that loss of neutral did not occur, merely that injury was not sustained or, perhaps, not reported.

OK, this is how I see it.

For planning purposes, the home is a caravan.

For electrical purposes, it is a building and not a caravan as defined in BS 7671.

It is unclear whether the chassis is an extraneous conductive part or not. It appears to rest on a concrete pad, so probably not. However, if it is an extraneous CP, it should be bonded i.a.w. 411.3.1.2(v) because it is an exposed metallic structural part of a building.

Were the chassis inaccessible (or possibly accessible only by using a tool) and not connected by metal to anything inside the building, it would not need to be bonded even if it were an extraneous CP because it would not be exposed.

The Caravan / Lodge sits on a concrete pad. Not sure if anything else inside building connected and accessible.