2 separate TT supplies into building?

danny1978spark · Aug 21, 2015

This gets a bit complicated so bear with me. Basically i have 2 rural tt supplies. One is to a large farm shed with PV solar 3.6 kw on the roof and is not used much.
the other is a large house and pub combined which has a shared supply transformer with a nearby bungalow. I m not concerned about the bungalow.The pub /house also has geothermal heating at 10kw i think. I have not done any work to this previously but do install PV Solar so know my way about it.At present the pub s PV goes against the geothermal when it's producing, lay mans terms.
Farm shed is mainly exporting as rarely used so ower has run a 16 mm split concentric cable between pub and farm shed and wanted to power the geothermal in said pub from farm shed supply thus using this generated power leaving the pub s solar to run the fridge's etc. when producing.
This would work in theory but i have no intention of hooking it up as i have many reservations. This Solar installer had recorded the pub s earth spike as 30 ohms when i measured it i got 1622 ohms. I had to install new spike which i managed to get 155 ohms. Unbelievable really, plus the farm building spike was 88 and was recorded as 27 ohms plus had a 30 ma trip completely stuck , wouldn't even push button test . Both jobs with major fire hazards.
Back to main topic then, i don t know enough about the distribution side but was worried about there being a second supply into the pub as a fire hazard. Was sure there would problems with the earthing as the various pumps etc. at the geothermal would link the 2 spikes of the supplies together or maybe raise the potential somewhere, urinal is all metal. Ouch. This is more for curiosity than anything.Sorry if it s hard to follow

Richard Burns · Aug 21, 2015

I would say that you should not have a problem with mixing the two earthing systems as you have the same earthing system for both supplies and it will not affect any of the distribution network.
Of more concern to me is moving the solar installation across to another supply meter and mixing the two incoming supplies.
If they are not supplied from the same source this could be catastrophic and if the solar is relocated to another MPAN then the FIT application would be invalid.

danny1978spark · Aug 21, 2015

Thanks for the reply Richard, each of the PV Solar would stay with its existing meter , no changes involved but because the geothermal was installed 2 years ago it would be possible to use the 16mm split concentric to feed the new consumer unit installed with it thus feeding the geothermal and thereby having any saving through the farm shed PV used in this process. I had a concern that because the internal pipework at the pub would then be earthed to both spikes, possibly through bonding conducters or the body of a pump then under a fault condition the path would be to the lower value spike or possibly both thereby causing a nuisance at best or possible danger.This is all worst case scenario but because of the risk to members of public in the bar i would like to be better informed and know what i m talking about . Also i would warn the landlord of the risks because so other fella will end up hooking it up without a care in the world, sods law.

davesparks · Aug 21, 2015

The issues I can see are how has this split con been installed? And how will you go about fulfilling the requirement for a single main switch for the pub installation?

In basic principle the joining of multiple earth rods together is an improvement in the earth connection,