PV Earthing

[smegal]

I will stop spamming soon. Just going through a steep learning curve.

I am looking to earth my installation. Unfortunately, my 25m roll of 4mm earth cable is too short. What is the most cost effective, but safe way forward. Do I file the 25mm roll away and order a 50m roll, or is there another way? Can I use an earth rod? IS it advisable/safe? I'm connecting back to house earth via the AC isolator. Is this correct?

[AGT]

If the cable isn’t mechanically protected 4mm 2 is too small.

What earring arrangement do you have at the incomer?

[nowty]

To earth or not to earth PV mounting frames, that old chestnut. No comment from me as there are several answers and each one is slightly correct or slightly wrong or doesn't matter depending on what your setup is, what you read and who you speak to.

Page 40 of the MCS guide has a decision tree which then leads you to BS7671 (IET Wiring regulations) if you decide to earth.

https://mcscertified.com/wp-content/upl ... TRONIC.pdf

More than likely he has TNS or TNCS earth, he has an earth henley block in his DNO cupboard from his cut out.

Picture of his DNO cut out cupboard from his other thread.
https://postimg.cc/8j657mWw

[Stinsy]

Earthing and bonding is a complicated topic! And I’m not entirely clear precisely what you’re talking about.

- Are you running DC cables from your panels to an inverter in your house? Or is the inverter local to the panels and you’re running AC to your house?

- What kind of cables are you using (SWA/hightough/“solar”)?

- What kind of earth does your house have (TT/TN-S/TN-C-S)?

- Are you talking about connecting the frames of the panels to earth?

Now like I say, earthing/bonding is a complicated topic and you could end up creating a dangerous condition by trying to do the right thing. Imagine you have a ground-mount solar array, you connect the frames to the earth connection of your TN-C-S supply. Then in the event of a PEN-fault the panel frames would raise to mains voltage and could kill someone touching them. This is because the person is outside and in contact with Earth (capital) whereas someone inside is protected by the various bonding (basically everything raises to mains-voltage and they have no access to Earth so cannot get a shock).

General rule: anything outside (solar panels/outbuildings/hot tubs/EV charging points etc.) should be isolated from the supplier’s earth and instead be protected with an earth spike.

[smegal]

Earthing and bonding is a complicated topic! And I’m not entirely clear precisely what you’re talking about.

- Are you running DC cables from your panels to an inverter in your house? Or is the inverter local to the panels and you’re running AC to your house?
DC cables to inverter in garage

- What kind of cables are you using (SWA/hightough/“solar”)?
"Solar"

- What kind of earth does your house have (TT/TN-S/TN-C-S)?
I'm not sure off the top of my head. I'm away form home at the moment but if you could tell me the difference, I can see if I can remember. The house is a reasonably new build (2017) if that makes a difference.

- Are you talking about connecting the frames of the panels to earth?

Yes

Now like I say, earthing/bonding is a complicated topic and you could end up creating a dangerous condition by trying to do the right thing. Imagine you have a ground-mount solar array, you connect the frames to the earth connection of your TN-C-S supply. Then in the event of a PEN-fault the panel frames would raise to mains voltage and could kill someone touching them. This is because the person is outside and in contact with Earth (capital) whereas someone inside is protected by the various bonding (basically everything raises to mains-voltage and they have no access to Earth so cannot get a shock).

General rule: anything outside (solar panels/outbuildings/hot tubs/EV charging points etc.) should be isolated from the supplier’s earth and instead be protected with an earth spike.

This does feel like the approach I should be taking. It doesn't feel right connecting something outside to the house's earth.

I've responded in red.

Looking at my probable earthing arrangement, I may be making things worse by trying to bond to my house's earth (not to mention potentially breaching regs).

[smegal]

To earth or not to earth PV mounting frames, that old chestnut. No comment from me as there are several answers and each one is slightly correct or slightly wrong or doesn't matter depending on what your setup is, what you read and who you speak to.

Page 40 of the MCS guide has a decision tree which then leads you to BS7671 (IET Wiring regulations) if you decide to earth.

This seems to be pretty clear that I do need to earth.

https://mcscertified.com/wp-content/upl ... TRONIC.pdf

More than likely he has TNS or TNCS earth, he has an earth henley block in his DNO cupboard from his cut out.

I have a feeling you are correct.

Picture of his DNO cut out cupboard from his other thread.
https://postimg.cc/8j657mWw

Good memory on my meter box! I went looking for photos to check.

[ALAN/ALAN D]

Say you live in the country with a medium voltage distribution transformer feeding just your property. The ( Supply voltage between 1000 volts and 33000 volts A.C. )
If the Gentlemen that normally drive about in Vans Towing Caravans.
Decide to remove the earth cable that runs from the earth rod up to the top of pole to the double wound transformer. Things can start to get a bit naughty.
Depending on your house Earth system

The problem gets worse if the double wound ( Medium voltage transformer ( Up to 33000 volts ) supply transformer insulation breaks down between the two phase high voltage transformer and your 240 volt supply to the house. ) Things have now got a lot more Naughty.

Bottom line.
Fit earth rods into the ground and run cable to your metal frame of the P.V. Panel mount.
If the first rod gets banged in 1.5 metres into the ground then bang the second rod into the ground 3 metres away from the first rod.

If your near the p.v. Panel mount structure your in with a chance.


Inside the house not as good.

[smegal]

Say you live in the country with a medium voltage distribution transformer feeding just your property. The ( Supply voltage between 1000 volts and 33000 volts A.C. )
If the Gentlemen that normally drive about in Vans Towing Caravans.
Decide to remove the earth cable that runs from the earth rod up to the top of pole to the double wound transformer. Things can start to get a bit naughty.
Depending on your house Earth system

The problem gets worse if the double wound ( Medium voltage transformer ( Up to 33000 volts ) supply transformer insulation breaks down between the two phase high voltage transformer and your 240 volt supply to the house. ) Things have now got a lot more Naughty.

Bottom line.
Fit earth rods into the ground and run cable to your metal frame of the P.V. Panel mount.
If the first rod gets banged in 1.5 metres into the ground then bang the second rod into the ground 3 metres away from the first rod.

If your near the p.v. Panel mount structure your in with a chance.


Inside the house not as good.

"Bottom line.
Fit earth rods into the ground and run cable to your metal frame of the P.V. Panel mount.
If the first rod gets banged in 1.5 metres into the ground then bang the second rod into the ground 3 metres away from the first rod."

I am tending to agree. Thankfully, I found water in my mount excavations, so the ground should be good for TT earthing.

[Stinsy]

Earthing and bonding is a complicated topic! And I’m not entirely clear precisely what you’re talking about.

- Are you running DC cables from your panels to an inverter in your house? Or is the inverter local to the panels and you’re running AC to your house?
DC cables to inverter in garage

- What kind of cables are you using (SWA/hightough/“solar”)?
"Solar"

- What kind of earth does your house have (TT/TN-S/TN-C-S)?
I'm not sure off the top of my head. I'm away form home at the moment but if you could tell me the difference, I can see if I can remember. The house is a reasonably new build (2017) if that makes a difference.

- Are you talking about connecting the frames of the panels to earth?

Yes

Now like I say, earthing/bonding is a complicated topic and you could end up creating a dangerous condition by trying to do the right thing. Imagine you have a ground-mount solar array, you connect the frames to the earth connection of your TN-C-S supply. Then in the event of a PEN-fault the panel frames would raise to mains voltage and could kill someone touching them. This is because the person is outside and in contact with Earth (capital) whereas someone inside is protected by the various bonding (basically everything raises to mains-voltage and they have no access to Earth so cannot get a shock).

General rule: anything outside (solar panels/outbuildings/hot tubs/EV charging points etc.) should be isolated from the supplier’s earth and instead be protected with an earth spike.

This does feel like the approach I should be taking. It doesn't feel right connecting something outside to the house's earth.

I've responded in red.

Looking at my probable earthing arrangement, I may be making things worse by trying to bond to my house's earth (not to mention potentially breaching regs).

Just seen the pic of you cutout. You have a TN-C-S. So definitely don’t connect the frames to that earth.

I wouldn’t earth the frames of the panels at all! The DC circuit is isolated from earth so is irrelevant. You’d be protecting against the frames being exposed to mains voltage and someone coming in contact with them and Earth simultaneously. The only scenarios I can imagine this might happen are just too fantastical for me.

If you want to drive an earth spike and link it to the frames, be my guest. Then if someone drapes a defective extension lead with exposed line conductor across the panels, the earth spike will ensure enough current is pulled to trip the overcurrent protective device in the event the RCD is faulty.

[smegal]

Thank you all very much. This has set my mind at ease.

I may just sink a rod as it can't do any harm, but you make a good point about the scenarios. Where I have a knowledge gap, I tend to try to overcompensate on risk mitigation in case I get something wrong.