additional cu cable size

[malcolmsanford]

Yes but seemingly no according to the DTI.

I can only relate to normal electrical practices and if you were in a domestic installation and taking a sub main out to an out building, if that building have metallic parts to it either a metal service such as a water pipe, or the construction of the building was metal, then you would need to bond the extraneous conductive part back to the MET if you were exporting the PME earth. If you were not exporting the earth perhaps because the building was a long distance from the origin of the supply, then most likely you would TT system.

There is obviously a reason the German electrical industry do not export earths on a PME, to which I don't know, and so it seems they insist on the array being bonded via a separate rod. I have no problems with this as such, as long as you are not having other metal work at a different potential that can be touched while your working or touch the array frame, and I used the example of perhaps an aerial mast that is earthed via a PME/TN-S from within the equipotential zone.

 

[Ramjam]

I'd suggest that the most common earthed metalic object on a roof is the metal flue of a central heating boiler.

 

[dansk]

I find I a bit of a headache trying to the do the right thing, I spent hours last night researching pme and bonding, it seems a very grey area to me, but my thoughts are if it's roof mounted take the bond to the met rather than a rod, let's say somehow you could reach the array from inside the zone it would have to be bonding to the met anyway. But did come across this on my travels last night Geosolar DC Earthing which explains in simple terms

 

[dansk]

What if you was holding onto the scaffold and the array at the same time and it was bonded to pme? Would that cause a shock?

 

[SolarCity]

The issue is, as I see it, that in the event of a fault which took the neutral out at supply, the array would become 'live' and potentially lethal to anyone working outside of the property.

 

[dansk]

The issue is, as I see it, that in the event of a fault which took the neutral out at supply, the array would become 'live' and potentially lethal to anyone working outside of the property.

Sure - But isnt PME "multiple earth" so the neutral conductor is earthed in stages along the line from the supply? But if broken neutral in CU then is a problem

 

[SolarCity]

Sure - But isnt PME "multiple earth" so the neutral conductor is earthed in stages along the line from the supply? But if broken neutral in CU then is a problem

Exactly. And this is what creates the potentially lethal situation.

 

[malcolmsanford]

In section 9 of the ESQCR-2002 covers PME in LV installations. The DTI impose stringent guidelines that the distributor must adhere to when supplying the PME system, and one of these is the loss of a neutral. The distributor take measures against the loss of the neutral conductor, and it is therefore seen as a low risk occurrence, which is why exporting an earth is not seen as potentially dangerous as it once was.

 

[dansk]

:dizzy2:

 

[Mark Davey]

[h=2]

Re: additional cu cable size[/h]

The issue is, as I see it, that in the event of a fault which took the neutral out at supply, the array would become 'live' and potentially lethal to anyone working outside of the property.​

not only the array but also all bonded exposed conuctive parts?

 

[SolarCity]

All parts that weren't part of the equipotential zone.

 

[malcolmsanford]

not only the array but also all bonded exposed conuctive parts?

on the Frame all there would be are panels and cable, as the panels are class II equipment and the cable is double insulated then there can not be any exposed conductive parts.

I agree that the cables can be damaged by fauna, but that is more of an external influence.

 

[dansk]

So whats the morel of the story here? bond, not bond, take to the MET on PME, take to earth rod on PME? - its a minefield.

 

[malcolmsanford]

Not really Dansk the DTI tells you I believe that if you need to bond the frame and the earth system is a PME then you are going to rod and you have to do as they advise.

My part in all this is that the DTI seemed to be applying German installation methods on the UK system, and IMO that is not correct. I'm sure if someone came on from the DTI and explained why this is, then we would be a lot better informed.

 

[dansk]

Cheers, I realise we need to follow the dti, even if we think otherwise. Some interesting points have been raised, and especially the point about chimneys coming through the roof. Could you confirm for me on a pme with a velux, take the bond to the met? And as above say a metal chimney is poking through it would be safer to take it back the met rather than a rod in that case.