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PME on closed landfill sites

Damo

Two closed landfill sites have a public supply with the cutout labelled as PME. Both are long closed sites so now a large field effectively with some pumps on control panels spread across the site. The PME supply goes back to its time as a working landfill or in one case more likely it’s previous existence as a quarry. It therefore seems likely that when providing the PME earth the DNO knew the nature of the site.  Landfill sites, closed or not, are not a special location. Can the use of a PME earth on such a site be criticised?

Both sites have a couple of shipping containers as site buildings.  However they could be considered to be controlled by an instructed person so PME for mobile or transportable buildings could be allowed (717.411.4). For the first of these conversion to TT for the cabins is not straightforward since the area with the cabins is close to the building with the supply, surrounded by lampposts on the pme supply and possibly other underground earthed metalwork which could make proper separation from the PME earth harder to achieve.  If left on PME how should bonding conductors be sized? Section 717 says nothing about bonding conductor size which would leave it being sized according to the supply PEN. One site has 300mm2 live conductors coming out of the cutout whilst the other has parallel 35s. Section 717 asks for the bonding of the mobile or transportable units structure to the local MET.  However if the idea is to carry diverted neutral currents it would presumably need to go back to the MET for the site?

I’d appreciate any advice on this.

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    I presume your concern is lost neutral, and the general advice not to use PME in caravans and similar ?

    It may not be what you would do if starting the design again, but it has been working for some years ?

    Unless there have been an incident causing a review, or the LV supply is especially vulnerable - overhead singles or rotting consac, I'd suggest do nothing without good reason. For example being landfill, is  it the sort of place one should drive earth rods, or is there a risk to buried plumbing and so on ? It probably is not so bad as a site I recall being on where we decided not to dig or drive rods due to the risk of buried explosive ordnance, but even so there are no prizes for hitting a pipe full of methane.
    Unless heavily used, the containers are not much more or a risk to passers by than the lamp posts and there are plenty of those on PME supplies.

    In terms of general safety on a lightly used site, things like working RCDs maybe  more worthwhile.

    Bonding is a trickly one and may not be particulary practical to apply the BS advice if the main supply is massive compared to the supply to the cabins. In that sense an approach more similar to the street lights may be more sensible - I  presume they are in 4 or 6mm?

    Mike.

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  • 0

    I presume your concern is lost neutral, and the general advice not to use PME in caravans and similar ?

    It may not be what you would do if starting the design again, but it has been working for some years ?

    Unless there have been an incident causing a review, or the LV supply is especially vulnerable - overhead singles or rotting consac, I'd suggest do nothing without good reason. For example being landfill, is  it the sort of place one should drive earth rods, or is there a risk to buried plumbing and so on ? It probably is not so bad as a site I recall being on where we decided not to dig or drive rods due to the risk of buried explosive ordnance, but even so there are no prizes for hitting a pipe full of methane.
    Unless heavily used, the containers are not much more or a risk to passers by than the lamp posts and there are plenty of those on PME supplies.

    In terms of general safety on a lightly used site, things like working RCDs maybe  more worthwhile.

    Bonding is a trickly one and may not be particulary practical to apply the BS advice if the main supply is massive compared to the supply to the cabins. In that sense an approach more similar to the street lights may be more sensible - I  presume they are in 4 or 6mm?

    Mike.

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