I think I can see a rational for retaining PME inside, say, a garage. It is likely that there will be lights, sockets, and maybe a garage door mechanism fed from the main distribution board in the house. Therefore their associated metalwork and that of anything connected to them will be at the same potential (save for under a fault condition) as the potential at the incomer's earth. It would be essential that the body of a vehicle on charge is at the same potential, to avoid the risk of shock potential being developed between the car body, and say a metal clad light switch or socket. However, as already pointed out, in the event of a neutral/Earth disconnect fault in the network, there is a risk of shock potentials arising between anything in the garage and "True Earth" which maybe the floor. It strikes me that if the risk of electrocution from touching a connected EV under such conditions is significant, then so to is that from touching any part of the garage's electrical installation. Clearly this cannot be the case, or all garages would have had to be made TT long ago. I think the answer to why PME is allowed indoors but not out is simply that outside regularly gets wet. Inside far less so and there is PME connected metal work around. Consequently the impedance to True Earth is likely to be very much lower outside than in. So outside, a very rare event with very high impact; high risk of electrocution. Inside, same very rare event, but vastly lower risk of the consequences being catastrophic.
I think I can see a rational for retaining PME inside, say, a garage. It is likely that there will be lights, sockets, and maybe a garage door mechanism fed from the main distribution board in the house. Therefore their associated metalwork and that of anything connected to them will be at the same potential (save for under a fault condition) as the potential at the incomer's earth. It would be essential that the body of a vehicle on charge is at the same potential, to avoid the risk of shock potential being developed between the car body, and say a metal clad light switch or socket. However, as already pointed out, in the event of a neutral/Earth disconnect fault in the network, there is a risk of shock potentials arising between anything in the garage and "True Earth" which maybe the floor. It strikes me that if the risk of electrocution from touching a connected EV under such conditions is significant, then so to is that from touching any part of the garage's electrical installation. Clearly this cannot be the case, or all garages would have had to be made TT long ago. I think the answer to why PME is allowed indoors but not out is simply that outside regularly gets wet. Inside far less so and there is PME connected metal work around. Consequently the impedance to True Earth is likely to be very much lower outside than in. So outside, a very rare event with very high impact; high risk of electrocution. Inside, same very rare event, but vastly lower risk of the consequences being catastrophic.
G12/4 Issue 1 had the answer right there for the reading ... it's related to the connected load downstream of a broken PEN conductor, larger the load, the greater the risk, as the less capable an earth electrode of given resistance is of limiting the rise in touch voltage.
EVs are a large load.
So outside, a very rare event with very high impact; high risk of electrocution. Inside, same very rare event, but vastly lower risk of the consequences being catastrophic.
Sort of ... the HSL report that was commissioned back in 2011 doesn't really say "high risk of electrocution", but puts the ball-park in the range of"broadly tolerable" which translates to "if you can do something to reduce the consequences or the likelihood, you should do so".
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