Metal - clad buildings and the confused forum member.

3? The building has only ONE service connected, if more than one service is required due to the building being split into individual units (terrace like), those subsequent services can only be TT?


True or false?


That is a trick question?


If they are each an individual " premises "  and  "terrace like" and all the individual services were provided at the same time, a supply and metering in each individual unit, then a TN-C-S would be provided in each. There are thousands of business parks like that. The DNO provides that on presumption that they stay as separate units, usually the requirement is the fixed installation in each unit is compliant with BS7671.


That is fine, until someone knocks through the wall of two adjacent units to make a bigger unit, but keeps both services. Best laid plans and all that.


I have experience of some quite large metal framed buildings that are an individual premises and are detached, that have an original TN-C-S [PME]  single phase supply and later had an additional 3 phase supply added due to a vast increase in demand. Perhaps for economy whoever decided to implement this wanted to keep the original single phase supply also. For the additional 3 phase supply only a TT was offered. So you now have this steel building with a mixture of earthing systems. BS7671 can deal with this, sort of, but it highlights a quirk of the cliff edge created in standards between the supply regs and BS7671. 


In answer to the true or false, it must be false because the DNO may agree to do it in very specific circumstances, but in reality are likely to only offer TT.

3? The building has only ONE service connected, if more than one service is required due to the building being split into individual units (terrace like), those subsequent services can only be TT?


True or false?


That is a trick question?


If they are each an individual " premises "  and  "terrace like" and all the individual services were provided at the same time, a supply and metering in each individual unit, then a TN-C-S would be provided in each. There are thousands of business parks like that. The DNO provides that on presumption that they stay as separate units, usually the requirement is the fixed installation in each unit is compliant with BS7671.


That is fine, until someone knocks through the wall of two adjacent units to make a bigger unit, but keeps both services. Best laid plans and all that.


I have experience of some quite large metal framed buildings that are an individual premises and are detached, that have an original TN-C-S [PME]  single phase supply and later had an additional 3 phase supply added due to a vast increase in demand. Perhaps for economy whoever decided to implement this wanted to keep the original single phase supply also. For the additional 3 phase supply only a TT was offered. So you now have this steel building with a mixture of earthing systems. BS7671 can deal with this, sort of, but it highlights a quirk of the cliff edge created in standards between the supply regs and BS7671. 


In answer to the true or false, it must be false because the DNO may agree to do it in very specific circumstances, but in reality are likely to only offer TT.