The video teardown in post #16 is narrated by two UK electricians. I took notes, this is what struck me as important -
(1) "OLEV" - A UK grant scheme from the "Office for Low Emission Vehicles". User wants compatibility. A new requirement of the scheme, is that "as from July 2019 EVSE MUST be able to connect to the internet".
(2) TN-C-S is the most common earthing arrangement in the UK //See also
https://medium.com/@Voltimum/the-principles-of-protective-multiple-earthing-pme-c068f2f433acWiring Regulations (18th edition, section 722) FORBID TN-C-S for EVSE outdoor stations - other than for three specific exceptions.
"A PME earthing facility shall not be used as the means of earthing" //Wiring regulations, 18th ed regs, part 722
However, TN-C-S is an example of a PME system.
https://www.voltimum.co.uk/articles/do-you-need-install-earth-rod-ev-charge https://eocharging.zendesk.com/hc/en-us/articles/360024737931-18th-Edition-Wiring-Regulations Normal practice for outdoor EVSE is to add an earth rod, creating a local 'TT' system. Zappi 2 uses an exception to the TN-C-S rule to save the need for an earth rod.
My understanding is TN-C-S has the following features:
(a) From the source supply and up to the supplier fuse, Earth & Neutral are one single conductor ('Terre' & Neutral are Combined hence 'TN-C'). 'Terre' = 'Earth'.
(b) Along the route of this "Combined" conductor, there are "multiple earths". So TN-C-S is a 'PME' system, "Protective Multiple Earth". NOTE: The actual combined Earth/Neutral conductor itself is termed 'PEN conductor' or 'CNE conductor'.
Why is TN-C-S normally forbidden for outdoor EVSE? It is to allow for the case where the supplier's PME combined conductor (called 'PEN' or 'CNE') breaks outside your property. The current return path for both 'line to earth' faults and line to neutral (fault or normal use) is via the combined PEN conductor.
But if the PEN breaks, then even normal-use Neutral flow will go the easiest way to 'Terre' (Earth). Maybe a person is touching the car. The current cannot return via the failed PEN cable though. So it will opportunistically jump via the person into the floor that person is standing on.
* Question: Why is there no requiremnet for a house-local earthing rod in all installations, regardless of outdoor equipment? - the same scenario can occur indoors too.
Of the 3 exceptions mentioned above, two are pretty rare situations. The 3rd exception allows TN-C-S if the safety RCD cuts "Earth" as well as Live. Zappi 2 uses this method, hence saving the installer worrying how good a local earth they can create, especially regarding dry soil. The narrators like this feature, apparently MyEnergi/Notts University have notes explaining how they do this. It would seem to be basically the CT around the earth lead that trips the 'contactor' in the earth line.
(3) Zappi 2 provides energy mangement. Part of this relies on up to 3 external Current Transfomer inputs (note these can be direct wired or more conveniently the current value can be sent by RF link).
The RF link is "NOT wifi or Bluetooth" for reliability reasons. There is also a CAT5 socket. Unsure if the RF link still used then for CT, probably.
There is a danger you can blow the main fuse if other high current equipment is also running. Zappi 2 monitors whole system via CTs [+RF link] etc to ensure no main fuse overload. For instance
CT 1 on main supply to house //Main fuse eg 100A
CT 2 on cable to garage //MCB rating to garage eg 40A "sub-main line conductor"
Then program Zappi 2 to respect those limits //Is this via a page on an HTML server inside Zappi 2?
* Question: Assuming it is a real pain to replace a blown supplier's fuse, why is there not usually a high-current MCB immediately downstream from the supplier's fuse, thus protecting the supplier's fuse? Eg Maybe something just under the main fuse rating?
(4) When contact weld seen, the PCB mounted DPST relay just up from the LNE input connector disconnects L & E.
(5) The narrators say Zappi 2 incorporates a class A RCD into its PCB circuitry and a CT. Further, the same CT (with L, N through it) also monitors for DC current over 6mA.
(6) There is also a CT around Live, presumably they measure current draw this way.
(7) We know front right is a PCB mounted relay. Not sure what the 2 large black boxes at rear are. Rear centre looks like a transformer. Rear right looks like a relay.