http://www.iee.org/Publish/WireRegs/WiringMatters/Documents/Issue16/2005_16_autumn_wiring_matters_earthing_your_questions_answered.pdftry this link, it supports my understanding on the recent "Exported earth " thread that the supply to a garage may be TT'd due to the fact that it comes from a
PME supply.
Scroll right down, its the bit showing supplies to caravan pitches
Do I dare to comment on this thread????? ]
]
oh to hell with it!!
I can always run and hide in steptoes yard under that old mattress behind the fridge if it gets too rough!!
Good evening Nicky... nice article link.
Hows work m8..?
1) No one actually disagreed with the concept that a remote garage could be TT'd in the relevant circumstances. (e.g. long distances from main property, exposed earthy metal work, 'PME'{TN-C-S} or TN-S)
2) The original post was questioning the concept of an "exported earth" and the various hazards associated with it..
Which is why we started considering the reasons why you don't......
a) have "exported earths" with simultaneously accessibly non-bonded earth potential conductors/metal work.
B) have small C.S.A. conductors between two different earth systems TT & TN-?.
3) I think you will find there were some dual concepts going through the length of the thread...
(the very long thread..).. which occasionally got lost due to the length!
4) Part of the problem was a unique concept of "Touch Voltage" put forwards where it is only measured between fault & MET....
Unfortunately this is not verified by NICEIC technical reference manual section V29-17.
Also confirmed on the thread "Touch Voltage" on the Q&A section of this forum....which I assume we all now agree with?
5) another part of the problem was a unique concept of "PFC prospective fault current" put forwards where it only equals 5 or 7 times the MCB rating and it does not involve a fault of negligible impedance.
Unfortunately again this is not verified by NICEIC technical reference manual section V29-17. or NICEIC pocket guide 15, or BS7671.
Also this is confirmed on the thread "Prospective Fault Current" on the Q&A section of this forum.....which again I assume we all now agree with?
So as said....
don't think anyone actually disagreed that PME with remote garage in the relevant circumstances would be TT'd.
As said nice earthing article Nicky.. which I am sure will be of some help to some of those still taking C&G's etc.. nothing like reinforcing the basics! ; \