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Author Topic: Earth and Neutral  (Read 6623 times)
stephendv
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« on: December 06, 2010, 02:03:20 PM »

Hi all,

After 3 years of waiting, I'm finally installing my inverter and battery system and have a few general questions around grounding.

1. The inverter manual says that neutral and earth must be joined together somewhere outside the inverter. So was thinking of doing it in the AC distribution panel - is this the correct place to do it?

2. The generator has it's own ground spike and the inverter system has a different ground spike about 10m away from the first.  The two ground spikes are not directly connected with copper externally (i.e. there's no direct copper wire from 1 spike to the next).  But they are electrically connected since there's only 1 common AC ground in the inverter - and both spokes are connected to this ground.  Any issues with this?

3. I have an easy to use ground bus bar where all the system grounds are connected to.  The bus bar in turn is then connected to the ground spike outside.  Can I connect DC ground and AC ground to this same bus bar?

Diagram attached.
 


* ground.jpg (33.63 KB, 800x572 - viewed 1758 times.)
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Justme
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« Reply #1 on: December 06, 2010, 04:59:51 PM »



For the inverter you need to bond the E & N before the house CU otherwise the RCD will not work.

You could fit a link in the inverter, meter or in the CU before the main switch.

If you run direct (or passed through esp on Victrons as they turn off the software bond option on pass through) from the genny you also need to bond before the rcd fitted to the genny (if you have one) so that the cable from the genny to the inverter is also protected by the RCD. Once you have done this do not use the genny as a stand alone portable one (not likely in your case I guess)

Now the bit I am not sure about.

Earth rods. I thought that you should only have one earth rod & all items should connect to it.
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Alan
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« Reply #2 on: December 06, 2010, 05:17:44 PM »

More is good.
Depends on the soil type as to how effective the earthing system will be.
And how many / what lenghth you will need.
There is no significant gain in putting multiple rods close together.
The earth rod spacing should not be less than the earth rod length.

Regards

Alan
« Last Edit: December 06, 2010, 06:26:28 PM by Alan » Logged
rogeriko
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« Reply #3 on: December 06, 2010, 07:17:53 PM »

Be careful doing this not all inverters like having their ground and neutral joined together you could well blow the thing up. If they were designed to be connected like this they would have been from the factory. All small transformerless quasi sine wave inverters will definately go up in smoke immediately.

First read all 7 pages of this thread on earthing inverters

http://www.navitron.org.uk/forum/index.php/topic,9766.0.html

Personally I wouldnt do it, leave both live and neutral floating you will not get a shock if you touch one of the wires by mistake. The only reason you get a shock from the mains is because the power company uses ground as a return to their generators.
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Justme
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« Reply #4 on: December 06, 2010, 08:01:47 PM »

As his manual says it must be done that gets round the blowing it up.

(most that dont like it are never intended for a fixed install)

As your method stops the RCD working what is your suggestion for increasing the safety back up to what it would have been had you added the bond?

As for getting shocks, I just hope that you never have a double system fault as your gonna die.
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rogeriko
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« Reply #5 on: December 06, 2010, 09:06:18 PM »

Of course if you can connect it properly so that the RCD will function safely then thats the way to go. I live in a country where RCDs rarely exist and if they are installed they always have a by-pass fuse installed next to them shorting them out so they are useless anyway. Both methods have their pros and cons, supposing your ground rod connection corrodes outside then the rcd will not trip because you are not connected to/using the neutral of the power company, because you are off grid, so then all your metal grounded appliances are connected to the neutral of the inverter. In dryer climates not Britain a 2 meter ground rod is not sufficient to run a 2kw load if connected between live and ground. We have many problems here when the neutral connection on the power pole breaks and the house ground just cannot cope with the load. I live off grid no connection to power company therefore no reliable ground/neutral my inverter is not neutral ground connected.














britain
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Justme
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« Reply #6 on: December 06, 2010, 09:39:18 PM »

1, Of course if you can connect it properly so that the RCD will function safely then thats the way to go.
2, I live in a country where RCDs rarely exist and if they are installed they always have a by-pass fuse installed next to them shorting them out so they are useless anyway.
3, Both methods have their pros and cons, supposing your ground rod connection corrodes outside then the rcd will not trip because you are not connected to/using the neutral of the power company, because you are off grid, so then all your metal grounded appliances are connected to the neutral of the inverter.
4, In dryer climates not Britain a 2 meter ground rod is not sufficient to run a 2kw load if connected between live and ground.
5, We have many problems here when the neutral connection on the power pole breaks and the house ground just cannot cope with the load.
6, I live off grid no connection to power company therefore no reliable ground/neutral my inverter is not neutral ground connected.


1, So that ends that discussion then.
2, So you are hardly well placed to offer advice for a UK based system that is wired correctly/safely.
3, The RCD could still trip due to earth bonding of internal metal work, But even if not the MCB will if a third fault develops which would be needed to pose a risk.
4, Why would you want to run a load via the earth? You just need a few milliamps to flow to trip the RCD.
5, It should not cope its not meant to.
6, With a system even you accept as not being the best option (see point 1 in your post).
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30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
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24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
stephendv
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« Reply #7 on: December 07, 2010, 08:15:54 AM »

Thanks all.  Nice link to that 7 paged thread on earthing  Roll Eyes 

Rogeriko, as I said the manual for the Sunny Island 5048 specifically states that it does not have a neutral to earth bond but that it requires the installer to make that bond somewhere outside the inverter.

Justme, my gen doesn't have an RCD so during pass through it would use the N-E bond I make in the distribution panel.  The ground can get very dry in summer and the lower areas start to become rocky.  I'm going to use 3 spikes, 1.2m each and space them 5m apart with bare copper connecting them all, hope that will do it.

Someone in the previous thread made an interesting comment though: that with N and E bonded, if the earth bond failed then you'd effectively have all the metal cases connected to a floating neutral, which is surely a big safety issue?
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Justme
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« Reply #8 on: December 07, 2010, 09:33:20 AM »

The metal cases will still be connected to the system earth that the RCD uses so that alone should still make the RCD trip.
(I will have to check that)

Also remember how many faults you need for that to be a problem.

1, earth rod fails
2, high impedance in the internal earth stopping any current (well not any but over 30 milliamp) travelling via that route
3, a live wire fault
4, you touching a live & an neutral bonded metal part

Even if the RCD wont trip you are only then back to where you were before you bonded the N&E & still needing 2 faults in the system

Our genny does not have an RCD either (it has mcb's so I could change them). I have used armoured cable to provide the protection & its going in a trench as well.


Our inverter does allow us to software bond it but on pass through it disables it so I have now bonded it at the first connection outside the inverter (just happens to be at the meter). Then all the inverted & pass through power is sorted.

On the dry ground issu cant you place the rods near to your soak away?
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30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
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24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
stephendv
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« Reply #9 on: December 07, 2010, 01:24:08 PM »

Just want to double check where the N and PE link should be made, when you say "before" the RCD does that mean between the inverter and the RCD?  I ask, because I've now had 2 different spanish electricians tell me that it has to be made after the RCD...
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Justme
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« Reply #10 on: December 07, 2010, 06:36:15 PM »

At any point before the RCD.

Just like it would be in a house install.

So yes between the inverter & the CU / RCD.

If it was after the RCD how could the RCD detect the imbalance between the L & N if the E & N both feed into the rcd's same terminal?


Basically if the L is handling 1amp then the N should also have 1amp passing through it. If the E is taking some of the 1amp then the imbalance shuts it down. If you join the E&N after the RCD then any power via the E will still get to the N terminal & get balanced with the L.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
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