Discrimination?
What if the supply is TN-C-S? Exporting earths?
yes what if?
Absolutely nothing if there are no extraneous-conductive-parts in the garage, which there probably aren't
Quotes from another forum from a member who works for a DNO:
"In terms of the PME supply, as others have said, most DNOs do not allow the PME earth to be exported out of the equipotential zone for safety reasons. The earth should be insulated at the "shed" end of the SWA cable, and the shed connected as a TT installation, using an earth rod."
"Under certain system conditions, a voltage can be present between the PME earth conductor and true earth, the most dangerous condition being the fortunately rare "broken neutral" in the supplier's network. The salts inherently present in concrete, actually make it a reasonable conductor, therefore it will be close to "true earth" potential."
"The rule about not exporting PME is actually a condition placed on the installation by the DNOs, not the Wiring Regs. It is interesting that most people are suggesting RCDs and larger bonding conductors as the answer - they are not. The problem is that in certain fault scenarios, it is actually the PME earth conductor which can have a dangerous voltage on it, measured to true earth. As you cannot have a switch or protecive device in an earth conductor, it can still be dangerous even after the RCD / MCB has operated."
"Consider the following worst-case scenario:
A house fed by a 2-wire overhead PME supply. An overheight vehicle brings down the bottom wire (which must be the combined earth & neutral according to the supply regulations).
In the house, everything will stop working, as they now only have a phase, and no neutral return. No mcbs will operate, as there has been no fault in the house, so all loads will remain connected.
Consider the MET:
Connected to the supplier's (now open circuit) earth & neutral conductor. Also through through the cutout to the installation's neutral, then via the resistance of everything switched on to the phase conductor, which is still live.
There will not be a hazard inside the house, as the bonding has caused everything to rise to the potential of the MET - no voltage difference, therefore no electric shock."
No hazard inside the house but imagine the hazard outside of the equipotential zone, a detached garage for example and appliances with exposed conductive parts (class 1). There will now be a potential between their exposed metalwork and true ground.
Now ask your DNO if they allow exporting of earths on a PME supply.
