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I have sat considering where we are likely to get a surge from which the surge protection built into the appliance will not protect from, but in the consumer unit it will, the size of the unit in the consumer unit is unlikely to protect from a lighting strike, neither is it likely to absorb enough energy to rupture the DNO fuse, and loss of PEN and resulting high voltages is not really a surge, so about the only thing I can see has changed is micro generation.
So can micro generation produce a surge? I think unlikely as there is so much included in the grid tie inverters to insure should the supply be lost, it will fail safe, however there is clearly a time period between a DNO supply failure and the micro generator inverters closing down, however the consideration seems to be over head lines, not micro generation when considering inclusion of SPD's.
The same problem as earth rods with TN-C-S also exists with SPD's, if every one from one transformer has either personal earth rods or SPD's then if required the energy dissipated is shared between all the homes on that supply. So with a new build estate great, but unless shared then the energy dissipated by one device is simply not enough.
I saw the result of a radio hams shack supply using a 4 mm² earth cable from the CU to shack when the PEN was lost, little balls of copper, OK with a 65Ω earth rod no problem, but the 4 mm² was bonded to the earth bar in the shack which was connected to 4 earth rods with bare copper tape between them for the radio transmitter so was better than my meter could measure, I would say less than 1Ω. He had realised there was some thing wrong, turned off main isolator to house, and called me on 2 meter as this had not stopped the earth wire melting.
It was caused by some road works, and the DNO said it was impossible, but responded very quick, and the radio ham was only person in street not to loose equipment, since he had turned off the main isolator before his wire burnt out. Why the person wiring his shack had used twin core SWA and not used the SWA as earth I don't know.
But had the supply been PME and actually had multiple earth rods it could not have happened, but TN-C-S is not always PME.
So are we being asked to install earth rods and SPD because those who should be fitting them the DNO and micro generators are not fitting them?
So can micro generation produce a surge? I think unlikely as there is so much included in the grid tie inverters to insure should the supply be lost, it will fail safe, however there is clearly a time period between a DNO supply failure and the micro generator inverters closing down, however the consideration seems to be over head lines, not micro generation when considering inclusion of SPD's.
The same problem as earth rods with TN-C-S also exists with SPD's, if every one from one transformer has either personal earth rods or SPD's then if required the energy dissipated is shared between all the homes on that supply. So with a new build estate great, but unless shared then the energy dissipated by one device is simply not enough.
I saw the result of a radio hams shack supply using a 4 mm² earth cable from the CU to shack when the PEN was lost, little balls of copper, OK with a 65Ω earth rod no problem, but the 4 mm² was bonded to the earth bar in the shack which was connected to 4 earth rods with bare copper tape between them for the radio transmitter so was better than my meter could measure, I would say less than 1Ω. He had realised there was some thing wrong, turned off main isolator to house, and called me on 2 meter as this had not stopped the earth wire melting.
It was caused by some road works, and the DNO said it was impossible, but responded very quick, and the radio ham was only person in street not to loose equipment, since he had turned off the main isolator before his wire burnt out. Why the person wiring his shack had used twin core SWA and not used the SWA as earth I don't know.
But had the supply been PME and actually had multiple earth rods it could not have happened, but TN-C-S is not always PME.
So are we being asked to install earth rods and SPD because those who should be fitting them the DNO and micro generators are not fitting them?