Why does the EVSE need its own earth rod if you already have one at the house?
First off, I'm not a sparky, just an engineer who's taken a deep interest in the discussions elsewhere & tried to drive to get a concensus. The TT-house model wasn't discussed deeply, as the video supplied by an expert summarised that scenario as simple, and concentrated on the more complicated T-N-C-S setups. My statement here
"EVSE will need an earth Rod, or must have PEN-Loss protection device fitted."
does
not say that the EVSE in the TT scenario needs it's
own earth rod. That's your reading.
An Earth rod is needed, somewhere, and as far as I'm concerned the sparky can advise on that. Are two better than one? Not my call. I'm not qualified to. But I'll happily comment & feedback what I've understood so far to be the concensus, and if I've got it wrong somewhere, I'm sure a lot of other guys can as well. I welcome better information.
How would a PEN-Loss device work on a TT earthing system with no supplier PEN?
I think the PEN-loss device is not needed if you have TT, because the Earth Rod clamps the car's bodywork to Ground potential (safely low). Otoh, if you insisted on activating it, e.g. because your EVSE comes with it, then if it trips, it will be isolating the earth-rod-connected E wire from EVSE to the car, at the same time as the L+N get disconnected. So it's isolating the car by pulling the charging plug out (in a virtual sense of course), exactly as it would in the PME setup, but at the same time also disconnecting the Earth rod as well! So I can't see any gain in safety tbh. So no point paying for this feature if you already have, or prefer, an Earth rod system. Unless someone else can some extra benefit.
The only noticeable difference in behaviour I can think of, is the PEN loss system triggers
after a small leakage current has passed down the E wire from EVSE to car's bodyshell, from there to your fingers, then through you to the ground outside, giving you a very brief shock. I guess this might feel like a decent static shock sometimes felt when unlocking the car in summer? Whereas this won't happen with the Earth-rod setup, providing that's in good order and conducting adequately.
The risk that the earth rod or PEN loss device is mitigating is the loss of the star point to earth connection at the substation allowing the phase voltages to differ and pulling the neutral voltage away from true earth and raising the potential of the body of car relative to the ground it is standing on. If you have an earth rod at the house, the amount of ground potential difference between the car and the earth rod would be tiny.
That makes sense. So can I take it that you're happy to have the TT-connected house using just the house's own Earth rod for the EVSE as well? If qualified sparkies on here are happy with that, fine by me.