While busy with the process of registering for solar generation in CoCT, I was told that my inverter cannot simply combine neutral and earth when Eskom goes down.

According to the provided example diagram (I understand it comes from something called an NRS document), it was explained that I need a double pole (I only have single phase) change over switch and an earth pole connected to my inverter, so that when the inverter binds neutral and earth, the inverter itself is grounded.

At the moment, my MP II does bind neutral and earth, so I do not have a floating neutral, but apparently I have a floating earth in the form of the inverter's enclosure?

Any assistance with this would be greatly appreciated. The way my wiring was done, if I understand the electricians SLDs correctly, to bring both live and neutral from the main DB down to the sub DB by the inverter into a double pole breaker, then into a double pole changeover switch, that then either take neutral and earth back to the main DB through another double pole breaker or to the inverter through a different double pole breaker. The inverter would then feed to the main DB also through the latter break.

At least this is how I understand it.

Does the regulations require me to now also knock in another earth pole that always grounds the inverter? It seems that this is a requirement with or without PV generation. Note that where the municipal wires come into my house, I do not have any breakers, but I do have a neutral bar that connects the incoming earth and neutral as I understand it (might be completely wrong if this doesn't sound like a normal thing in a TN-S system).

2 hours ago, jykenmynie said:

At the moment, my MP II does bind neutral and earth, so I do not have a floating neutral, but apparently I have a floating earth in the form of the inverter's enclosure?

apologies to any electricians, and the forum members in the know, reading this...

As far as I think I know the Multi's connect enclosure to chassis to AC-in earth internally in any case (unless double insulated enclosure probably) - but connecting the chassis separately/again to earth leaves a bit of redundancy. This should not require a separate earth rod/spike. But do not take my word for it ... earthing/grounding/bonding TNS-S... TT...GT...Gti ...makes my head still hurt a bit 🤕

Seen in reverse: earth conductor (wire) from consumer (e.g. plug) -> sub DB->  inverter (including MP-II enclosure) -> main supply  -> supply source will (should?) be unbroken. While inverting with neutral and earth bonded in the inverter, the neutral to earth link for AC-out is maintained via the earth conductor even though the AC-in neutral to the main supply/supply source is broken (unless the MP-II ground relay is disabled via VEConfigure). 

from wiring unlimited

Okay, time for the schooling to begin....I expect many red crosses..... and/or tears  on my answer sheet ....

Edited July 8, 20205 yr by introverter
added pic

4 minutes ago, introverter said:

As far as I think I know the Multi's connect enclosure to chassis to AC-in earth internally in any case

Okay, that would be great. I'll just double check my sub DB but I think there is an earth coming into it as well. In that case, why would that diagram from the NRS (whatever this is) require another earth electrode?

Aaah man... when people don't know the product, but they have the power to say yes or no... then you get crap like Goodwes not being questioned and Victrons being questioned...

The Multi puts the TN bond in AFTER it has disconnected the neutral from the grid. It never bonds T and N without first disconnecting N, so from the grid side there is no visible bond If a sparky from the city actually went to your kiosk and measured it, he would found it floating.

The Multi has a relay test that it runs through every time it connects to the grid. This checks 1) that there is no TN bond on the output, 2) That there is a TN bond on the input, 3) that closing the bonding relay on the output works. That clickety-clack it does before it connects to the grid... it's flipping all the relays back and forth. Only then does it connect to the grid. In other words: It will not connect to the grid if the bonding relay is stuck.

It only bonds TN when running islanded. As it should.

The Multi never interrupts the earth. The earth terminals on AC-in, out, and the case itself are all interconnected internally. This is also exactly as it should be, because earths must be continuous. I usually advise people to explicitly earth the case of the Multi using the provided lug, but this is really only to make it absolutely obvious to any inspecting sparkies and/or engineers that you did not leave the terminal open. And it's a belts and suspenders thing.

Also refer to SANS (this is from a draft copy of the 2017 regulations), point 6.1.5.2 b) :

That should settle it, right?

Thanks Plonkster! That settles it in my mind and if anybody questions it, I’ll copy paste your explanation. Except the first bit. 😄

The problem could be if that SLD is the one provided by your own electrician/installer to CoCT... the SLD implies that the earth neutral bond on the inverter is permanent..

6 minutes ago, introverter said:

The problem could be if that SLD is the one provided by your own electrician/installer to CoCT... the SLD implies that the earth neutral bond on the inverter is permanent..

The SLD wasn't that detailed, I'll need to find time to draw it up myself at this point... The SLD I received only showed the lives, neutrals and ground in each DB, where it is going etc. I'll have to augment it with the breakers, batteries, proposed PV etc.