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Discuss TN-C-S + earthing in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

C

charlie

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Why on a caravan site or some other outbuilding does the earth have to be an earth electrode and not the earthing on the supplying TN-C-S ???
 
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R

Reg Man

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Why on a caravan site or some other outbuilding does the earth have to be an earth electrode and not the earthing on the supplying TN-C-S ???
Your main earth on a TNCS system is actually connected to the neutral conductor. If the electricity boards supply neutral went down there would be no neutral or earth. Thus anything that should be neutral or earth will become live. Hence the stake.
Sounds good anyway!!!!. I'm sure thats right.
 
C

Cirrus

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That's also as I understand it too Reg Man.
 
W

wayne

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not being the resident expert,shakey did a post about exporting the earth and why it was a bad idea
 
S

Shakey

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  • #6
Your main earth on a TNCS system is actually connected to the neutral conductor. If the electricity boards supply neutral went down there would be no neutral or earth. Thus anything that should be neutral or earth will become live. Hence the stake.
Sounds good anyway!!!!. I'm sure thats right.
pretty much, Regman, although given that the neutral is live anyway....

way is see it, N is earthed at the substation tranny, Supply N goes open circuit, load is drawing current, current will try to continue flowing to PME connection point at dis board, through neutral to open circuit, then down through nearest PME spike and back to origin

but of course, current flow through resistive earth path, V=IR, so a PD will develop on the installation earth system, which will have a different PD to the local earth and extraneous conductive parts (step and touch voltages anybody;))

this is the danger with the TNCS, in that the N &E are the same point in the installation incoming supply, and the circuit current will try to use the earth path in the event of the N going o/c
 
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