Earth neutral bond for inverter before I get grid hook up on new build.

[jimseng]

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Yes we used their earth bonding. I added the earth rod when we installed the batteries and backup gateway.

I'm sorry to keep banging on about this but it is a complex subject without a definitive answer and easy to get wrong (and I bet many professionals get it wrong despite their qualifications).
@kelvin. When you added your earth rod, did you leave the SSEN earthing permanently in place? It seems to me that inverters in islanding mode probably leave the existing earth in place, which potentially is fine until there is a local cabling fault. However an additional earth rod would surely introduce a ground loop if the DNO earth isn't disconnected in islanding mode.
Maybe I am over thinking it but it seems this isn't a settled subject yet, and it should be simple to get right with the correct information.

Edited 21 hours ago by jimseng

[JohnMo]

We had to add an earth rod in addition to the the SSEN one, for running in island mode.

 

But if you make some basic assumptions

1. Mains is off and cable is broken or in your case not there.

2. You no longer have a safe proven earth path.

 

So a fault in house has no earth route in island mode. So you need to add an earth spike for that condition.

 

No earth spike no ground route except via you. Doesn't sound that safe to me.

 

So install earth spike for island mode and be safe, would be my answer. 

[jimseng]

@JohnMoI get that. I think I am being really pedantic, and I am considering the long term. Again, probably over thinking it but there are a couple of scenarios. And I am talking about where I am on grid and there is a power cut:

1. Power cut downstream of local earth point. DNO earth still remains so local ground spike creates and earth loop. -Bad

2. Power cut due to cable fault. No DNO earth. Local ground spike is necessary, no earth loop. -Good

It seems a simple thing to fit a double pole relay to create the local E/N bond and at the same time swap from the DNO earth to local earth rod. But I haven't seen a single mention of this being done anywhere, which, in my experience, doesn't mean it shouldn't be done, just that it is a detail that is ignored/ nobody cares/ hasn't been discussed.

[Alan Ambrose]

>>> But I haven't seen a single mention of this being done anywhere

 

It's a more unusual requirement and a lot of real sparks won't have thought about it and the regs probably don't cover it well.

 

But, see e.g. 

 

https://foxesscommunity.com/viewtopic.php?t=139

 

Earth Neutral Bond :

 

https://www.facebook.com/groups/571819024654208/posts/1072959771206795/

 

 

[Kelvin]

3 hours ago, jimseng said:

I'm sorry to keep banging on about this but it is a complex subject without a definitive answer and easy to get wrong (and I bet many professionals get it wrong despite their qualifications).
@kelvin. When you added your earth rod, did you leave the SSEN earthing permanently in place? It seems to me that inverters in islanding mode probably leave the existing earth in place, which potentially is fine until there is a local cabling fault. However an additional earth rod would surely introduce a ground loop if the DNO earth isn't disconnected in islanding mode.
Maybe I am over thinking it but it seems this isn't a settled subject yet, and it should be simple to get right with the correct information.

Yes it’s permanently in place in that it’s part of SSEN’s cabling system. The earth rod is there for when the house goes off grid and you lose the DNO earth in case you have a fault in the house. Interestingly there was an urgent notice from Sigenenery to their installers about the correct earthing requirements for the system. Some installers weren’t connecting an earth rod at all and some were but not cabling it correctly in the gateway. 
 

There maybe is a multiple fault scenario where neither of these are sufficient but what would need to happen for that? 

[jimseng]

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The earth rod is there for when the house goes off grid and you lose the DNO earth in case you have a fault in the house.

This is the last piece of the puzzle for me and the bit I have been obsessing over, perhaps unnecessarily, but obsessing I am. I believe that when the house goes off grid the inverter disconnects the live and neutral but not the earth. That is certainly what the it shows in the Sunsynk and Growatt manual. Which means installing an earth rod gives two earthing points and therefore a permanent ground loop except  when there is a specific DNO cable fault and you lose the DNO earth. And it isn't discussed anywhere as if it has been completely overlooked.

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It's a more unusual requirement and a lot of real sparks won't have thought about it and the regs probably don't cover it well.

Indeed! But I'm thinking about it. And I can deal with it by installing a relay with an extra NO contact to swap the earth from DNO to ground spike. That means whatever the fault is that caused the grid failure, there is a bonded earth in the islanded house but never a ground loop. But since I have never seen this mentioned then either I'm fussing about nothing, nobody has noticed, which they should have, or I have got it completely wrong. 

I'll move on from this subject once somebody convinces me that I am an idiot or that everyone else except me is an idiot. It won't be the first time. (I'm not saying which way round either)😀

[Mattg4321]

2 hours ago, jimseng said:

This is the last piece of the puzzle for me and the bit I have been obsessing over, perhaps unnecessarily, but obsessing I am. I believe that when the house goes off grid the inverter disconnects the live and neutral but not the earth. That is certainly what the it shows in the Sunsynk and Growatt manual. Which means installing an earth rod gives two earthing points and therefore a permanent ground loop except  when there is a specific DNO cable fault and you lose the DNO earth. And it isn't discussed anywhere as if it has been completely overlooked.

Indeed! But I'm thinking about it. And I can deal with it by installing a relay with an extra NO contact to swap the earth from DNO to ground spike. That means whatever the fault is that caused the grid failure, there is a bonded earth in the islanded house but never a ground loop. But since I have never seen this mentioned then either I'm fussing about nothing, nobody has noticed, which they should have, or I have got it completely wrong. 

I'll move on from this subject once somebody convinces me that I am an idiot or that everyone else except me is an idiot. It won't be the first time. (I'm not saying which way round either)😀

I think you’re not fully understanding how it works. It’s a fairly complex subject though and it’s easy to get slightly confused about what exactly will happen in each scenario. It happens to me sometimes. 
 

I’m not entirely sure what you mean by earth loop and it being bad. I always associated earth loops with audio equipment and hum/noise. There is no mention of it in BS7671 as far as I can recall and I don’t see how this could be a safety issue. DNO Earth is the star point (neutral) at the transformer being tied to true Earth. Ie rod etc in the dirt. This will usually be done multiple times en route from transformer to your property - PME. 
 

If your property is a TT system - a minority of installations these days, but including caravans and building sites, then you have no DNO Earth connection on site. You whack a rod in the ground and your path to DNO Earth is through your rod and then through the dirt to the DNO Earth. You’re calling this a ground loop?? It’s a normal earthing system. 
 

If you’re in islanding mode, then the fault path will be back to the inverter and not back to DNO transformer. So the fact that you have tied your inverter neutral to earth via the neutral/earth bond relay and your own rod, means that is your fault path now. It doesn’t matter if you are still connected to DNO PME/TN-C-S system earth as this is no longer the fault path, as your power is derived from the inverter and not the DNO. 
 

You wouldn’t disconnect your bonding from the incoming gas and water supplies when in islanding mode would you. At this point, they are, electrically, just bits of metal in the ground, as is the DNO PME system. They are not part of the fault path. 

[jimseng]

I was of the understanding that if one has more than one earth point you have a potential for a path for stray current (e.g. lighting) from one point, through the equipment to another. 

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There is no mention of it in BS7671 as far as I can recall and I don’t see how this could be a safety issue

That's good enough for me. Thanks for all the responses. I'll stop worrying about it, get the electrician to fit a ground rod and get on with it.