residential park home

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Devon
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United Kingdom
hi, i've got to connect up some new, permanently sited park homes.
my question is do I have to put an earth stake down (the ground is made up on hard core) or can I use the supply company's earth which is TNS.
each home has a metal chasis frame which is bonded back to consumer unit, cheers
 
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I suggest that you don't do either of those things, and instead tell the owners/operators of the site to employ an electrician who knows what he is doing.
 
They may be permanently sited but legally they're classed as caravans, in a caravan site, to which special regulations apply
 
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agree with bas there, around here there are several of these parks with park homes, each park home has a tncs supply though.
 
When is a caravan not a caravan?
Section 721 says:-

They do apply to those electrical circuits and equipment intended for the use of the caravan for habitation purposes.

Not sure what a caravan is for if not for habitation purposes!!! But I would read that as meaning section 721 does not apply to mobile homes.

Section 717 would seem to apply. So we look at:-
717.411.4 TN System
in the UK a TN-C-S system shall not be used to supply a mobile or transportable unit except:
(i) where the installation is continuously under the supervision of a skilled or instructed person, and
(ii) the suitability and effectiveness of the means of earthing has been confirmed before the connection is made.

My Boss got into trouble connecting a cabin because he did not ensure there was a good earth. He glanded the SWA directly into the metal of the container and when it was lifted with a crane the steel wires pulled out of the gland and the cores made contact with the container making the whole thing live.

Personally I would have considered before lifting a cabin with a crane one should disconnect the supply! And I would have not blamed my boss. But that was not what the HSE said and he was blamed.

So looking at (ii) the suitability and effectiveness of the means of earthing has been confirmed before the connection is made. One wonders what is considered as "Suitable"? Clearly from what happened to my boss the SWA cable would need good quality cleats and I would want to use a core as well as SWA for earth.

Forgetting about regulations the problem is often the door is metal and the skin is metal so unlike a house where if there was a problem with PME then the whole house would float with neutral/earth and there would be very little where you could touch a earthed item and true ground. (The soil pipe is about only external bonded metal and often they are plastic) With the mobile you would be likely to be standing on a metal step or porch connected to true earth while getting hold of a door handle which would be bonded to DNO's earth system. I would therefore assess the risk as too high.

And to do a risk assessment is really the only method you can use. Where ground anchors are used one may consider these will ground the structure enough to ensure if the DNO was to lose their neutral/earth it would open a protective device other than the RCD and so is not a problem. But this is all part of the risk assessment. If a gale was to move the caravan would the power fail safe. i.e. will the earth wire be the last wire connected if the power cable is ripped out.
 

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