Earth Neutral bond for hybrid inverter (again)

[jimseng]

At the risk or reopening the can of worms and revisiting an old thread I am still wondering about the earth neutral bond relay in the event of a power cut. I have now ordered a Growatt 10k hybrid inverter and according to this diagram (from the Growatt manual) the earth neutral bond is permanent and provided by the DNO at the meter, or wherever it is. (Or at least it seems to be relying on the DNO E/N bond). In the event of a power cut it looks to me like the earth neutral bond still remains in place as the grid and home loads neutrals are connected and therefore the E/N bond is still intact.

I suppose here the additional E/N bond  relay would be necessary if there was a cable fault between the house and the DNO E/N bond, but doesn't that take place in the meter box?

I'll have to have a ground spike anyway given that my grid connection is a way off but once it is in place...what then?

[Mattg4321]

You won't have an earth-neutral bond once the grid is disconnected from your installation by the inverter in the event of a power cut. DNO earth-neutral bond isn't necessarily at your intake position either. It certainly won't be in a TN-S earthing system (although yours is likely to be TN-C-S (PME) if a new connection).

[jimseng]

In the image the load and grid neutrals are permanently tied so even in a power cut there is still continuity to the grid neutral. Surely, unless there is a cable fault, the bond would still remain?

[Dillsue]

8 hours ago, jimseng said:

In the image the load and grid neutrals are permanently tied so even in a power cut there is still continuity to the grid neutral. Surely, unless there is a cable fault, the bond would still remain?

As both the house loads and the inverter are connected to both the earthbar and neutral bars in the schematic, I take it that Growatt expect that E-N link to be within your house. It's a poor schematic if that's depicting the link to be out in the grid somewhere.

 

Probably worth asking Growatt for clarification??

[jimseng]

57 minutes ago, Dillsue said:

As both the house loads and the inverter are connected to both the earthbar and neutral bars in the schematic, I take it that Growatt expect that E-N link to be within your house. It's a poor schematic if that's depicting the link to be out in the grid somewhere.

 

Even if the link was in the grid somewhere, isn't it electrically the same? The trouble is it probably covers different countries and is a bit generic. I am wondering what UK people think. The Sunsynk manual has the same schematic.

[Dillsue]

3 minutes ago, jimseng said:

Even if the link was in the grid somewhere, isn't it electrically the same? The trouble is it probably covers different countries and is a bit generic. I am wondering what UK people think. The Sunsynk manual has the same schematic.

Its not electrically the same if the DNOs cable gets disconnected/severed which seems to be your concern?? Outside of your house isn't under your control but inside your house is, so you can ensure that link remains.

 

If your inverter meets UK grid regs then there will be people at Growatt that understand the UK grid so should be able to clarify things for you??

[SteamyTea]

Just a thought, possibly a bad scenario.

If there are a number of grid connected system, and one of them is an islanding system that is incorrectly wired in, so it does not disconnect from the grid, would the other systems still be connected and running?

I know that most inverters check that grid impedance as part of the running/disconnect protocol, but that may be within tolerances in a rural setting.

An unlikely scenario I know, but with millions of systems fitted, unlikely becomes inevitable.

[JohnMo]

18 hours ago, jimseng said:

Growatt 10k hybrid inverter

Are you trying to use a hybrid inverter in wrong situation - it's designed for grid connection - you don't have one.

 

Isn't the correct inverter an off-grid inverter?

[jimseng]

3 hours ago, JohnMo said:

Are you trying to use a hybrid inverter in wrong situation - it's designed for grid connection - you don't have one.

 

Isn't the correct inverter an off-grid inverter?

I don't have a grid connection yet, but I will have. Maybe not until later in the year.
I think the schematic is not really correct. I think the permanent neutral link is for other countries. I was under the impression that the neutrals are common until the grid goes down, at which point the grid is disconnected internally with a double pole relay, hence the need for an earth neutral bond relay, but it is hard getting the information. I have reached out to Growatt, I'll see if they come back to me.

[Mattg4321]

That schematic is wrong and potentially dangerous in the wrong hands. All 'live' conductors (this includes neutral, don't confuse live with line) must be disconnected from the grid when in island mode. This is a safety issue to protect people working on the DNO side.

 

The schematic shows the neutral from the load connectors connected to a common neutral bar with the grid neutral. This is wrong. Most, if not all, of these inverters are made for foreign markets and the instructions are either nonsense or dangerous when applied here in the UK imo.

 

I would like to imagine that the L&N are both disconnected from the grid entirely when in island mode, but I've not fitted a Growatt before. My Sunsynk does do this.