Gecko25

As another electrically inclined South African looking to stave off loadshedding and reliance on the incumbent utility,
I also find myself trying to make sense of the Earth-Neutral bonding story as it relates specifically to the Sunsynk/Deye devices but also all the inverter installs out there, here is my short answer conclusion (the looong answer follows):
The Load side Neutral bus should be bonded to the Earthing system bus ONLY when the inverter is operating in off grid mode, with a few very specific exceptions. The only sensible way to do this automatically is with an external N/O contactor powered by the ATS output (in the case of the SS/Deye system) or via a built in internal contactor (if the inverter supports it, not SS/Deye), or via a N/C contactor powered by the Grid side Live and Neutral (for all other inverter types without a E-N feature built in).
I come to my conclusion having read the SANS 10142-1 (specifically 2021 Edition 3.1) over and over trying to understand, and indeed trying to justify, why the majority of registered CoC grade electricians I have spoken to currently say they are making a permanent E-N bond at the inverter.
Unfortunately I still cannot justify their reasons, and I'm still trying to find out who gave this "directive" to do so, which to me seems to have become more of a broken telephone "it's what they say we must do" style argument. The best argument for permanent bonding I've heard is that relays/contactors are unreliable, which should not really be the case considering they are usually graded for hundreds of thousands of cycles and thousands of operations per hour. Nothing like what this E-N bond contactor should experience. I do agree that SS/Dey should have built in a monitoring system to ensure the E-N bond is made every time or disconnect the load, but that is not the discussion point I wish to raise.
 
Let me preface my research below with "I personally am not an electrician" and so do not have access to the "they's" of the registered electrician world, but I do have a background in engineering and enjoy a good deep dive into a subject to make sense of it, and this one is really getting to me.
I do hope that something definitive from a reputable source will come to shed light on this confusion once and for all (ie published officially in the government gazette or a letter penned and signed by a rep from Eskom or a large local South African municipal utility).
Until then, here are my arguments for using a the temporary bond including SANS references attached. Sorry if it is a  painfully long read.
 
My first reference is SANS 10142-1, page 231 section 7.12 Alternative Supplies.
The NOTE 2 in 7.12.1.1 states "This part of SANS 10142 does not cover the generation plant, integration and synchronising requirements of an alternative supply operating in parallel with the main supply to an installation"
The key word is parallel because this is EXACTLY what the SS/Deye units are. They have the capacity to run off-grid, but 99% of the time (well 60% in Stage 6) they are being utilised as an alternative device in parallel with the grid (ie grid-tied) not as an alternative device used "instead of" the grid (ie an off-grid device). A diesel generator that does not sync with the grid but is brought into use by a multi-pole change-over switch (break before make, auto or manual) is a good example of a "non-parallel" alternative energy device.
The regulations for a parallel (ie Grid-Tied) device appear to be contained in SANS 10142-1-2 "The wiring of premises
Part 1-2: Specific requirements for embedded generation installations connected to the low voltage distribution Network in South Africa". And the biggest problem with this is that 10142-1-2 is still, to the best of my knowledge, in the draft stages of publication (since 2020) . However it can be downloaded and read in draft form. And low and behold in SANS 10142-1-2 (Draft) page 43 section 6.1.5.2 "b) Where a system is designed to operate in Islanded mode, a neutral-earth switch shall be installed that forms a neutral-to-earth bond for the duration of the islanding operation only."
Now that should be the definitive answer right? ( ie use a temp not permanent bond for E-N when switching from island/off-grid to grid-tied/parallel modes), were it not for the fact that these regulations are still under draft review and therefore cannot be called definitive at this stage 🙄. In fact I may have been reading an older version of the draft and maybe this section has been or will be removed in the final print? Great.
 
So lets go back to SANS 10142-1:2021 Ed3, the current gazetted sparky bible for low voltage wiring of premises, and run through the scenarios for non-parallel alternative energy sources. Just to say we did.
Here we find:
Section 6.1.6 pg 79 (Installation requirements/General Circuit arrangements) "6.1.6 The neutral conductor shall not be connected direct to earth or to the earth continuity conductor on the load side of the point of control except as
allowed in 7.16.4."
Pretty straight forward, don't do it at the Load end of the line (ie after the house main incoming switch). But what of 7.16.4?:
7.16 relates to "Distribution systems as part of an electrical installation", ie complexes/multi dwellings where the utility (Eskom/municipality) supplies electricity to the complex and the complex submeters to each unit.
" 7.16.4 - Neutral Earthing
7.16.4.1 Whereas TN-C systems may be implemented along the distribution system backbone, the individual service connections at every distribution kiosk shall be TN-S.
7.16.4.2 From the point of supply to each user or part of a communal installation, the neutral and earth conductors shall be separate conductors""
7.16.4.6 A TN-S system shall not be converted to a TN-C system"
TN-S (Ground(terra)/Neutral-Separate) means the E-N is bonded at the source (usually transformer up the street, or at the diesel generator in the parking lot, ie at the source) and never again shall they be allowed to meet. TN-C (combined) means N & E are one wire from the source until it reaches a designated point down the line (designated by the system designer/utility at the design stage). This could be at the the kiosk in the street, at the entrance to the property or at the first/main distribution board of the dwelling, it is usually done as a cost saving measure (one less cable to run), somewhat at the expense of some safety. At that E-N bond point the N & E separate and become a TN-S system with the N & E never to again meet down the line (as affirmed in 7.16.4.6). Once a TN-S, forever a TN-S. Most urban dwellings are TN-S from the local substation, but more rural or older sites will be TN-C till the entrance of the property/building, where they split the N & E and become TN-S. Overall this is then referred to as a TN-C-S system. TN-S, TN-C-S systems pretty much cover household installations in South Africa, also I don't want to get into TT systems.
I digress, basically 6.1.6 says you shall not do an E-N bond on the Load end of the line and this is re-enforced in 7.16 where in fact you shall not do it at any location down line of the first E-N bond from the utility.
 
So why still the confusion, and willingness to violate the SANS code (under threat of a CoC fail)? Well here section 7.12 again makes it's appearance.
The part that seems to be causing the most confusion is on page 223 (10142-1:2021 Ed.3) section 7.12.3 "Earthing requirements and earth leakage protection" as it relates to "7.12 Alternative supplies" (remembering from 7.12.1.1 NOTE 2 that this section actually does not cover parallel/grid-tied alternative supplies, only non-grid-tied alternative supplies).
"7.12.3.1 Neutral bar earthing
7.12.3.1.1 Protection in accordance with the requirements of 6.7 shall be provided for the electrical installation in such a manner as to ensure correct operation of the protection devices, irrespective of the source of supply or combination of sources of supply. Operation of the protection devices shall not rely upon the connection to the earthed point of the main supply when the generator is operated as a switched alternative to the main supply."
So one cannot rely on the E-N bond that exists at the utility when running on an alternative off-grid supply, ie a new E-N bond needs to be made for the alternative supply. Makes sense, but how and where?
"7.12.3.1.2 In an installation that is supplied from a combination of transformers and alternative supplies located near to each other, the neutral points of each of these items shall be connected to a single earthed neutral bar (see P.1 and figure P.1). This earthed neutral bar shall be the only point at which the neutral of the installation is earthed. Any earth leakage device shall be positioned in such a way as to avoid incorrect operation due to the existence of any parallel neutral/earth path."
So indeed for an off-grid alternative supply the Neutral AND Earth from BOTH the utility AND the alternative energy supply can be bonded together in ONE location but ONLY if they are located NEAR to each other. This is the "few specific exceptions" I referred to earlier. This is pretty much never the case for an urban home looking to inject an inverter or install a backup generator into the house DB board. Read on..
7.12.3.1.3 Where alternative supplies are installed remotely from the installation, or from one another, and where it is not possible to make use of a single neutral bar or neutral conductor which is earthed, the neutral of each unit shall be earthed at the unit and these points shall be bonded to the consumer's earth terminal (see 6.12.4). The supply from each unit which supplies the installation or part of the installation, shall be switched by means of a switch that breaks all live conductors operating substantially together (see figures P.2 and P.4), to disconnect the earthed neutral point from the installation neutral when the alternative supply is not connected (see also 6.1.6)."
The "where it is not possible to make use of a single neutral bar or neutral conductor which is earthed" is the most common scenario encountered in the urban setting when alternative energy is wanted (diesel generator for example). In this case, each supply shall make an E-N bond themselves at their source, but they must have switches in place that only one of the suppliers E-N bonds gets connected to the essential load neutral bar at a time. 
To me it seems most likely that there is an earnest attempt make the info in 7.12.3.1.2 and 7.12.3.1.3 fit as the reason for permanently bonding the E-N at the outputs of an inverter that sits in parallel with the utility/grid. But:
a) the inverters under discussion are parallel tied inverters not off-grid, so 7.12 of SANS 10142-1 is somewhat irrelevant.
b) inverters in the domestic setting are usually nowhere near the main supply source (at best they may be near the TN-C -> TN-S bond, in a TN-C-S system) so bonding both supplies at the same source location is unlikely to be possible. If this were the case (maybe a farm with a transformer on a pole and the inverter sitting in a box next to the pole), then maybe the permanent E-N bond would be Ok (both supplies being E-N bonded all together on the SAME bar in the SAME location). 
c) where the supplies are not near to each other, they shall then each do their own E-N bond locally to their source, but they must be switched in such a way that the Utility/Grids Neutral (also the Inverter inputs neutral) and the Inverter output Neutral never share the same wire on the Load end of the installation. Figure P.2 shows this quite well where the the essential part of the DB sees only the Live/Neutral from the grid OR from the alternative supply, never at the same time. Since the Sunsynk bond the input and output neutrals when in grid-tied mode, this rule would be violated.
In conclusion, making a permanent E-N bond at an inverter tied in parallel down-line from the mains supply, on the load end of the line on a TN-S network to me seems to violate so many reasons that the Earth wire exists in the first place and a lot of SANS regs that relate to it. Why even have separate Earth and Neutral wires if we are just going to bind them together where ever we feel like it? There are very good safety  reasons to have a separate/redundant return path to supply source, which I don't want to get into. Every E-N bond done down line of the first one negates much of these benefits for all systems up line of that additional bond. There have also been good comments made that you risk becoming THE E-N bond for the entire are supplied by the substation should the sub find itself unbonded for "reasons".
The only way to satisfy 7.12.3.1.1 (no reliance on the utility E-N bond when islanding) and still run a parallel alternative supply device like the SS/Deye is with a temporary E-N bond that is only in effect when the device runs in island mode (off grid).
I have attached my references to SANS 10142-1 and 10142-1-2.
I do hope that SANS 10142-1-2 gets gazetted soon so that the debate can be concluded.
References SANS-10142 E-N Bonding.pdf