Hi ,
Thank-You for your input on this subject,
in a search on Neutral Earth bonding I came across this post,
I have a Deye 8KW Hybrid Inverter, I would like to install a Neutral Earth Bond relay for when the inverter goes into island mode.
I have read my manual extensively, however, unless I am wrong, I can’t identify the correct contact points to connect an external relay to the internal relay in the inverter, if there is in fact one.
Can someone assist?
Many thanks!
From the installation manual:
Not an electrician… But here goes.
Current SANS code regarding the earth neutral bond…
Now the bit I’m unsure on…
Is the inverter required to be on your main earth leakage? (I would think it is as they are usually in metal enclosures)
Having the permanent bond after the main earth leakage would make its operation unreliable.
As a final note… Surge damage is a lot more likely when there is a floating neutral.
Edit…
The earth neutral bonding boxes I’ve found are shown as contactors with an NC connection for earth-neutral. Coil is then actually connected to Eskom… Meaning regardless of what your inverter does the bond should engage as soon as Eskom is lost
No. As long as there are no sockets on the same line, and the equipment is mounted high enough that a small child cannot get to it, you only need suitable overcurrent protection. If you want to, you can fit a separate earth leakage for the inverter, and I’ve actually done that, but I used a 300mA unit.
The reason that I dislike this method, is there are legitimate reasons for the inverter to run islanded while the grid is also on. NRS097, for example, mandate that the inverter should monitor for 60 seconds before reconnecting to the grid. In that 60 seconds, you’re running islanded without a bond. It is also possible that the grid returns, with a voltage that is out of bounds, resulting in the inverter not connecting, but the contactor is still pulled in by the grid side.
The only way to properly do this, is for the inverter to activate the bonding relay.
Good to know the suppliers aren’t pushing out bad solutions…
Please Please Please, everyone do take note of this! Do not use Eskom as the reference as you can have a floating neutral for up to 10 minutes! That is bad.
You can use it as backup…
My preference:
I Really want to understand this debate thoroughly. I have drawn up a little “Scenario sketch” to illustrate my (possibly wrong) understanding:
If you have PV installed you most likely have an Earth-rod installed as well. Say your installer permanently bonded your Inverter Output Neutral to Earth.
Your minisub neutral bar gets stolen during loadshedding. The return path to the transformer-neutral of all the homes on that minisub takes place the moment your inverter synchronizes to mains and connects output Neutral to Eskom Neutral. Effectively connecting the neighborhood Eskom neutral THROUGH YOUR LITTLE EARTH BRIDGE to earth (and then to neutral back at the minisub). Earth carries the current of all homes back to the Eskom Neutral. Your main breaker will trip, but there might be a possibly-large explosion inside your inverter.
Am I missing something?
I’m a picture thinker.
This is what I’m told by a few people … unless an expert of your wiring, says otherwise.
… and then the fight started … 
Would your main breaker not trip before anything melts in your inverter? Presumably we are only concerned about the current that would pass through the inverter’s neutral to earth connection?
Anyways, perhaps this is a reason why output neutral and earth should not be permanently bonded…
Slightly off topic, but relevant: My dad used to read me “Lafras Cuyper - Kanonnier” when I was young. So I’m reading it to my daughter now. Last night, a scene played off in the book where a captain lambasted a youngster on not following rules exactly, thinking he knows better. He told him that these rules have been refined over generations and that thinking you know better is very arrogant and naive.
One of two things may occur… okay maybe three things
The upstream current through your house’s Neutral will be 2 to 3 times the rating of your breaker and it will trip
The current might be lower than your main breaker, but high enough to melt your 4mm2 earth bridge… this is bad
The current may be orders of magnitude higher than your main breaker and even worse there may be a fault current flowing due to a “downstream” short circuit, and the moment your inverter syncs to mains, that fault will flow through your main breaker, possibly causing it to explode
I am not an advocate for the permanent bond, but I am on my way to sign off a few sites next week and I know the latest NRS097 permits a permanent bond, but I want to dissuade the installer by laying out the facts, and fully understanding the risks and their likelyhood.
If P<>N current by 30mA+, then the E/L will trip.
I would say that breakers, and relays, are typically rated in kilo-ampere for explosion-level currents, so the breaker will probably trip before anything blows up.
But you make a good point here. For me, the almost more dangerous situation is losing a neutral but NOT the earth (and I also assume TN-S earthing, no local earth rod). So now there is a path from your house back to the transformer (on the earth wire), and the moment you bond the earth and the neutral at your place, you restore the neutral for everyone else in the street, giving them a path back to the transformer. Of course it will trip quickly, but it is a fault mode you probably want to avoid
From my thread at "power forum:
The latest revision of NRS (2024 edition) does not allow a permanent bond for exactly the reason we are discussing.
5.4 Neutral to earth bonding when forming an intentional island*
5.4.1 To prevent a SSEG neutral connection to the the utility neutral through an earth conductor when
the SDU opens, **the SSEG shall not have a permanent neutral bonding to earth
NRS-097-2-1-Published-2024.pdf (540.2 KB)
So what is the consequence of this for the cheaper off grid type inverters? Would they be doomed to have a floating neutral when islanded? I seem to recall that they do not have a relay that would enable an earth bond for neutral just when disconnected from the grid, but I could be mistaken.
It basically forces the installer to install an external “ground relay” by means of a contactor or other similar type of switchgear. (200mS or faster)
preferably engaged or disengaged by the inverter, NOT Eskom “coming back online”
Sorry, not “preferably” - the contactor/relay HAS to be operated by the control logic of the inverter as can be seen in the Standard.
Yo, what I read on other forums of experts advising how to connect these inverters … can but shake my head.
Indeed, and there are timing requirements as well. It must bond within 200ms after forming the island, and it must remove the bond no more than 200ms before reconnecting the grid. It is all in the 2024 version of NRS097.
An expert is merely someone a little further up the Dunning-Kruger curve
