House earthing from an off grid solar system

[Adymould]

Hi everyone, I live well off grid in Wales and am presently renovating a small property. As part of that renovation I have had a full off grid solar system professionally fitted coupled with a generator back up.

The inverter charger has a neutral earth link as does the generator. The inverter charger has a ground relay so that if the generator starts then the inverter charger disconnects its neutral earth link and the generator neutral earth link comes in to play. The system is earthed by two, 2.4m earth rods placed 3m apart driven in to the forest floor. The solar installation is 120m away from the property it supplies and a 3 core, 25mm, SWA cable takes the supply from the solar installation up to the property.

My question concerns the earthing arrangement at the property 120m away. I'm categorising the solar installation as a TN-S system - your thoughts?

As the supply cable to the property is 3 core can I use the third core as my sole earth or should I be sinking earth rods at the property end and creating a TT arrangement?

I've had quite conflicting opinions, professional opinions, thus far and would really appreciate a solid and logical answer.

Very many thanks.

 

[mariopanuchi]

Seems interesting. ON my solar installation they advised a small gap between the top and bottom panels to allow the heat to escape. This prolongs their life and allows for better efficiency.

 

[bill01803]

IIt all should be TT and should be protected so. There are experts here that will tell you what the value of the rod should be for a stand alone system.

 

[Adymould]

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IIt all should be TT and should be protected so. There are experts here that will tell you what the value of the rod should be for a stand alone system.

Thanks Bill, that’s what I’ve done in the end. I knew I could go TT, but not ever so familiar with off grid I wondered if there was a better way. I’ve got the Ze down to just below 100 ohms at the property with a couple of 2.4m rods and trips/operating times of my RCBO’s are all good and well in limits.
I might try and achieve a better earth in time for summer but I’m happy where I’m at for now.
Many thanks for your input.

 

[marcuswareham]

I don't know for sure, but why must this be TT ??

Surely this is the same as how we set up generators to be TN-S for live events all the time?

If you have 3 conductors going from the generator and solar already why not use one for the earth, this is a much better, more reliable and lower impedance connection rather than relying on the ground and soil to connect your earth to the generators neutral

If it was set up as TN-S and the generator still has an earth electrode this is not in any way a TT system as the generator earth electrode is only used to reference its neutral to ground (much like the electrode at substations), for example the system would work perfectly well without any electrodes and in which case would be an IS system, although this is not recommended due to fortuitous earthing present risk that might not have been considered

As far as I know you are completely allowed to set up your own TNS system and I would favour it over TT, the only thing you are not allowed to do is set up your own TNCS system under the electricity safety, quality and continuity regulations

 

[Adymould]

I don't know for sure, but why must this be TT ??

Surely this is the same as how we set up generators to be TN-S for live events all the time?

If you have 3 conductors going from the generator and solar already why not use one for the earth, this is a much better, more reliable and lower impedance connection rather than relying on the ground and soil to connect your earth to the generators neutral

If it was set up as TN-S and the generator still has an earth electrode this is not in any way a TT system as the generator earth electrode is only used to reference its neutral to ground (much like the electrode at substations), for example the system would work perfectly well without any electrodes and in which case would be an IS system, although this is not recommended due to fortuitous earthing present risk that might not have been considered

As far as I know you are completely allowed to set up your own TNS system and I would favour it over TT, the only thing you are not allowed to do is set up your own TNCS system under the electricity safety, quality and continuity regulations

Thanks Marcus - much appreciated. Everything you say makes sense to me and was part of the dilemma that I was having.
There’s a few threads on here about exporting the earth relative to TN-S and TN-C-S systems that have divided opinion and added ‘fuel to the fire’ too!
I’ve also had divided opinion about whether in my particular off-grid scenario that the I have a TN-S or a TN-C-S. All good info too from fellow professionals, but with varying opinions.
I guess the upshot is that the scenario and decision is mine and so I’ve gone TT.
Thanks for the input. I’ve learnt some stuff about generators too!

 

[marcuswareham]

Thanks Marcus - much appreciated. Everything you say makes sense to me and was part of the dilemma that I was having.
There’s a few threads on here about exporting the earth relative to TN-S and TN-C-S systems that have divided opinion and added ‘fuel to the fire’ too!
I’ve also had divided opinion about whether in my particular off-grid scenario that the I have a TN-S or a TN-C-S. All good info too from fellow professionals, but with varying opinions.
I guess the upshot is that the scenario and decision is mine and so I’ve gone TT.
Thanks for the input. I’ve learnt some stuff about generators too!

The treads about "exporting" TN-C-S earths are not relevant in your case, these are about using a TN-C-S earth from the national electricity grid outside of an equipotential zone. As in your case you are completely off grid and not connected to the electricity supply network it doesn't concern you as you are not exporting any earths.

I have only just seen how old the original post is, so yes as your say you have done it all now and your right it is your choice at the end of the day

Iv attached some pictures of the earthing arrangments I have mentioned, etc just for a bit of information

Thanks

 

[Wilko]

I’m of the thought that more rods = more good.
The cable that links the generating facilities will need to have a CPC and I’d be using this at the house and adding more rods at that end. All the rod installation locations should be sufficient by themselves to satisfy loop disconnect but I parallel them to increase reliability. This would seem to be “TNS supply with local rod support”.

 

[Adymould]

The treads about "exporting" TN-C-S earths are not relevant in your case, these are about using a TN-C-S earth from the national electricity grid outside of an equipotential zone. As in your case you are completely off grid and not connected to the electricity supply network it doesn't concern you as you are not exporting any earths.

I have only just seen how old the original post is, so yes as your say you have done it all now and your right it is your choice at the end of the day

Iv attached some pictures of the earthing arrangments I have mentioned, etc just for a bit of information

Thanks

Thanks Marcus - much appreciated.

 

[Adymould]

I’m of the thought that more rods = more good.
The cable that links the generating facilities will need to have a CPC and I’d be using this at the house and adding more rods at that end. All the rod installation locations should be sufficient by themselves to satisfy loop disconnect but I parallel them to increase reliability. This would seem to be “TNS supply with local rod support”.

Thanks Wilko. The 3rd/earth core is earthed at the generator end incl a cpc link to the sheath. At the property end it is capped off in its own Henley block and no cpc link to the sheath to keep the two entities separate.
TT is the direction I’ve gone in and now that I have I’m having a little ‘play’. I’ve got 2 x 2.4m rods paralleled at the solar/generator site. I put 1 x 2.4m rod in at my property (120m away) and got a Ze of 146 ohms. I paralleled that with a second 2.4m rod 3m away which dropped the Ze to 100. The ground at the property is s as mixture of clay ‘topsoil’ descending into shale.
Id like to drop the Ze below 100 now to cope with summers dryer ground later so I’m going to place another parallel rod. I’m expecting to get another 30ish ohms drop.

 

[Wilko]

Id like to drop the Ze below 100

Yes, good idea. I’ll set you a target to beat - I’m at 6 Ohms now and stay under 10 year round, ha ha .

Dont ask how many rods ...

 

[Adymould]

Yes, good idea. I’ll set you a target to beat - I’m at 6 Ohms now and stay under 10 year round, ha ha .

Dont ask how many rods ...

??

 

[mariopanuchi]

Seems interesting. ON my solar installation they advised a small gap between the top and bottom panels to allow the heat to escape. This prolongs their life and allows for better efficiency. I found and recomend this article websolarguide.com/am-solar-flashlight/

Great solution!

 

[Adymould]

The treads about "exporting" TN-C-S earths are not relevant in your case, these are about using a TN-C-S earth from the national electricity grid outside of an equipotential zone. As in your case you are completely off grid and not connected to the electricity supply network it doesn't concern you as you are not exporting any earths.

I have only just seen how old the original post is, so yes as your say you have done it all now and your right it is your choice at the end of the day

Iv attached some pictures of the earthing arrangments I have mentioned, etc just for a bit of information

Thanks

Marcus, can I tap you for an opinion on my generator output. I’ve contacted the SDMO tech dept but little to no joy yet.
I have an SDMO Kohler KD425-2 diesel 10000E Silence with MODYS 9kW generator. Only 260 hours on the clock. It’s voltage output over a minute ranged from 235 to 249 volts with the frequency varying by 0.6 Hz around the 50Hz datum.
For me, this is all over the place compared to what I’m used to in my house.
In my off grid situation when we are running from the generator it trips off our combi boiler which never happens when running from our solar arrangement.
What’s your opinion of the volts and frequency please.