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logic28 avatar image
logic28 asked

Grounding of-grid- grid assisted

We all know that a good grounding for a small group of units yields for units and components bonded at just one main ground rod.

My concern is that if I connect the Multiplus AC in it will automatically join the inverter Neutral/case ground to that of the incoming AC practically connecting two different ground points (house rod and solar shed rod) at a given distance which is wrong.

I have already separated the PV ground mount from the solar energy building precisely for that very reason.

How do installers resolve this problem is my question but most importantly what can I do to avoid dual grounding rods?

Grounding
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mvas avatar image
mvas answered ·

You wrote ...

We all know that a good grounding for a small group of units yields for units and components bonded at just one main ground rod.
How do installers resolve this problem is my question but most importantly what can I do to avoid dual grounding rods?

You are misunderstanding basic home wiring.
It is very common, almost required in the USA, to have two or more ground rods.
Typically, we bond the Neutral Bus Bar and Ground Bus Bar at one location,
usually in the Main Breaker Panel.
When a MultiPlus is installed and goes off-grid ...
it Breaks / Opens the connection in the Hot and Neutral wires coming in to the MultiPlus.
Now the Neutral Wire in the house becomes un-grounded.
So, the MultiPlus closes the "Ground" relay.
This action will bond the home's Neutral Wire to Ground, at just one point, inside the MultiPlus.

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logic28 avatar image logic28 commented · 
It is very common, almost required in the USA, to have two or more ground rods.
Typically, we bond the Neutral Bus Bar and Ground Bus Bar at one location,
usually in the Main Breaker Panel.

That is what I've always thought until I did some research and found this interesting series of video analyses/tutorials from the US that completely disrupted my way of thinking as it makes a lot of sense.

https://www.youtube.com/watch?v=Ypo99VRxT44

Jump to minute 3.09 but the rest is most interesting too.

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mvas avatar image mvas logic28 commented ·

Yes, I have watched that video. And now I just watched it, agan. This video does not change this fact ... The "active" Neutral Bus Bar is connected to the Ground Bus Bar in one, and only one, location. When I add new Grounding Electrode Conductors (GEC's) then I use an Intersystem Grounding Bridge ...

https://www.mecampbell.com/media/catalog/product/cache/4556987fc6258dfb00e1de307ed01009/i/d/id-pic-v1-gbb5-2.jpg

I connect all of my new GEC's to the original GEC that connects my Ground Bus Bar in my Main Panel to my original Ground Rod. This is done outside of my home. I created a Grounding Array, but still with one, and only one, GEC entering my home = safe. There is no such thing as the house ground rod vs the shed ground rod, because all ground rods, PV Frames and Ground Mount are connected together outside = The Ground Array.

Finally, I run a green ground wire from the Multiplus PE terminal back the Ground Bus Bar in my Main Panel.

When I am on-grid, my neutral wire is only bonded to the Ground Bus Bar in my Main Panel. When I am off-grid, my neutral wire is still only bonded to the Ground Bus Bar in the Main Panel via the ground relay and the green wire. Electrically speaking, my neutral bonding has not changed and there are not any new GEC's inside my home.

I agree, do not wire your house like the picture you posted below.

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logic28 avatar image logic28 commented · 
When a MultiPlus is installed and goes off-grid ...
it Breaks / Opens the connection in the Hot and Neutral wires coming in to the MultiPlus.
Now the Neutral Wire in the house becomes un-grounded.
So, the MultiPlus closes the "Ground" relay.
This action will bond the home's Neutral Wire to Ground, at just one point, inside the MultiPlus.

Understood, so presumably it will remain closed even when the Multipus is in charge mode only correct?

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Kevin Windrem avatar image
Kevin Windrem answered ·

Keep in mind that the ground rod is NOT a current carrying connection. The resistance is high. In fact the resistance may not be low enough even to trip a 20 amp breaker. As mias says, there is no issue connecting multiple ground rods to the safety ground network of wiring.

It IS important that all safety grounds in a facility be connected together so that any fault currents can flow to the ground-neutral bonding point and trip breakers. Your PV frame SHOULD be connected to other safety grounds, not isolated from them.

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logic28 avatar image logic28 commented · 
screenshot-2023-07-14-at-220729.jpgIt IS important that all safety grounds in a facility be connected together so that any fault currents can flow to the ground-neutral bonding point and trip breakers. Your PV frame SHOULD be connected to other safety grounds, not isolated from them.

That is what I've always thought until I did some research and found this interesting series of video analyses/tutorials from the US that completely disrupted my way of thinking as it makes a lot of sense.

https://www.youtube.com/watch?v=Ypo99VRxT44

Jump to minute 3.09 but the rest is most interesting too.

I have a PV-to-ground bonding cable installed of the same size as the three strings namely 10mm (8AWG) each string thus only sufficient to discharge any static/transient electricity due to wind or else, but if I bond this with the rest of the equipment's ground, as I have seen done so many times, I would effectively create the exact situation that Mike Holt is telling us to avoid since the four Ground Mount metal posts are buried in concrete by 4' across 15m creating in effect a second grounding point at 20m from the primary ground.

Of course, I could have used the posts in concrete as the only ground point for all but I would have to find a way to feed a much larger cable into the underground ducting capable to suit all also due to the distance.


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screenshot-2023-07-14-at-220729.jpg (510.1 KiB)
Kevin Windrem avatar image Kevin Windrem logic28 commented ·
He is saying for safety against lightening you MUST bond all auxiliary electrons to the safety grounding system in the facility. In your case that means you need to bond your PV support structure to the AC safety ground. If you do not do this and the ground near your array is stuck by lightening, the current from the lightening will flow through other conductors and could damage equipment due to voltage differences between the two earth connections.


I'll be the first to admit that a near by lightening strike is likely to cause damage anyway but the recommendations will minimize any in-building currents.

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logic28 avatar image
logic28 answered · 
He is saying for safety against lightening you MUST bond all auxiliary electrons to the safety grounding system in the facility.

My apologies for misprinting the time in the video, it is 13.09 where I heard him saying to only ever use one and only one point of reference into the earth. However, he also mentions bonding everything underground together and the same for all above-ground still at only one point of reference into the earth. This is the confusing part but I have to assume that all below-ground being bonded can be considered one point of reference to the earth, am I correct?

For that, as I said before (but not clearly), I have a bonding connection between all my underground items hence the 4 ft concrete encased PV framework and the 8ft grounding rod at the solar shed where all the equipment is installed, cable sufficient for medium currents (8AWG) since, in the event of lightning, the current would travel at a frequency in MHz and for the well known "skin effect" it would travel outside the conductor itself making the size of the cable to a degree irrelevant.

This image shows what I prepared in order to have one and only one reference point.

img-20230715-064204-522.jpgGoing back to my initial concern, if I then connect the grid assist cable to the inverter I would then have a ground rod coming from the house 35m away which is not bonded to the rest of the below-ground items if not for the external conductor itself.

Would that make it wrong?





img-20230715-064204-522.jpg (156.1 KiB)
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ejrossouw avatar image ejrossouw commented ·

The latest UK regulations stipulate that for a system that can operate in island mode, you cannot rely on the earth from the grid as it can be severed (e.g. TNCS carries both N & E in a single cable from the substation to your property) and can leave you without any earthing and therefore you have to install a dedicated earth rod for your system.

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logic28 avatar image logic28 ejrossouw commented ·

Thanks, I have an independent earth rod for my system so I am not worried about my grounding, the fact is that if I wanted to recharge the batteries for testing purposes I might need to draw power from the grid instead of from the generator, so long as it is not a problem, in which case what would I do? Should I just connect live and neutral or would that be wrong too?



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mvas avatar image mvas commented ·

What is stated in the video is not confusing. In my previous post I added a URL link showing how all of the external GEC's are easily combined at one point. Exactly per the instructions in the video. And that video is now somewhat outdated, due to newer NEC regulations. We use an "Intersystem Grounding Bridge" which is UL approved in the USA. Nothing homemade, is allowed. Maybe, you need to post a wiring diagram.

I do not understand this: "... Grid Assist Cable ..." What is that? There is an AC IN connector (wires from your main panel) and an AC OUT connector (wires to your loads) on the Multiplus.

Are you mounting your Multiplus, 35 feet from your house? 35 feet of AC wire from the house and then 35 feet of AC wire back to the house? So, you are adding a total of 70' Feet of high amperage wire between the Main Panel and your loads? Voltage Drop?

We mount the Inverter adjacent to the Main Panel = extremely short / fat wires.

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ejrossouw avatar image ejrossouw mvas commented ·
My understanding is the OP only requires the AC from the property to charge the batteries occasionally and it is some distance away.
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daza avatar image
daza answered ·

@ejrossouw correct this all started around EV’s and hot tubs and has been pushed more as DNO’s start to walk away from providing earths going back to old school the introduction of foundation earthing at some stage but it’s unclear if @Logic28 is in the UK I’ve not seen much if any grounding on rails for solar on a roof, one thing they have introduced is DC surge protection for the DC side bring this inline with the AC side well at least in the UK. As to two earthing points be careful and make sure you abide by your regs for distance and placement as the last thing you want is it jumping from one rod to the other

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ejrossouw avatar image ejrossouw commented ·
The earthing of the PV frames as far as I am aware is to solely serve in the event of highly unlikely lighting strikes when looking at the UK. Indeed I am aware not even on commercial installations in the UK is it used I was told by professional installers.
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logic28 avatar image logic28 ejrossouw commented ·

I don't think the PV ground or anything else would provide any adequate lightning protection but more like dump any static electricity generated by wind or something else.

However, as you can see from the image above, I have installed three surge protectors next to the fuses (and they need a grounding point) followed by the breakers and finally by the disconnects, one per string, in order to isolate each line if needed.

Three more isolators are placed at the receiving end in the combiner box with a further surge protector for any potential surge downstream from the PV array (lightening striking the earth creating a spike in the line)

This three strings independent lines system allows me to disconnect one or more strings from inside the shed for servicing as well as enabling me to run a much larger set of individual cables which will more than cope with the length and for a larger current should the PV provided more than rated (general rule multiply the amperage by 1.25) My case each string 12A x 1.25 = 15A

So I run 6 x 10mm wires plus earth.

Reference Method B (enclosed in conduit on a wall or in trunking etc) 10mm = 57A

I only have 15A each

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mvas avatar image
mvas answered ·

Here is the NEC review explaining what I have been telling you. A single Green EGC, Equipment Grounding Conductor, connects between the Inverter PE and the Main Panel Ground Bus Bar. While ALL of the GEC, Grounding Electrode Conductors, (usually bare copper) for PV Frames, Metal Rack, PV Ground Rods, etc connect together outside of the house. NOTE: We do not connect the Inverter to any GEC (Ground Rod). Same goes for every other device in your home. You do not add a ground rod to your washer, dryer, stove, hot water tank, furnace etc. They are ALL grounded via the Green EGC wire, back to the Main Panel Ground Bus Bar. The same applies to your Inverter. The Inverter does not connect to any existing Ground Rod or any optional PV Ground Rod. The Inverter is ONLY grounded via a Green EGC Wire back to the Main Panel Ground Bus Bar, exactly like every other metal appliance powered by your Main Panel.

https://youtu.be/cZo8ict33_I

All PV Frames, Metal Racks and optional PV Ground Rod ( was required by my inspector! ) was connected with a Bare Copper Wire which then gets bonded back to that Bare Wire, by your AC Meter, between the two AC Ground Rods and your Main Panel. I have a "Grounding System", with all wires GEC's connected outside of my house.

If you add a PV Ground Rod and you decide to connect it your Inverter PE, via a bare GEC then that becomes your "problem". It will work. It may, or may not, be a problem when lightning strikes. We don't do that.

The National Electric Code has finally realized and admitted that adding an extra PV Ground Rod and bonding them directly to the Inverter, can be more dangerous.

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logic28 avatar image logic28 commented · 
If you add a PV Ground Rod and you decide to connect it your Inverter PE, via a bare GEC then that becomes your "problem". It will work. It may, or may not, be a problem when lightning strikes. We don't do that.

That is exactly what my question was about and that is exactly what I intended to do but mixed opinions came about reading.

My PV is grounded for static electricity or induced currents and, in my case, for the delivery box surge protectors (I combine at the shed), no bonding between the PV and main panel ground busbar where all the equipment connects to one central point to then reaches the Ground via the ground conductor.

That said the PV is naturally grounded by the encased concrete base so it becomes a "below-ground earth point" which, as I understand from the video, should be bonded to any other underground electrodes in order to avoid unwanted current flowing through the equipment cable potentially damaging whatever they go trough (inverter etc)

I laid the grounding cable between the PV and the shed just in case so that I can connect if I decide to do so.

However I'm not connecting to any meter, and I'm not near the house so these instructions do not exactly apply to my case and I would very much like to see what the NEC would advise for Off-Grid System.

Even though I'm not in the US I very much appreciate how things are handled there



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ejrossouw avatar image ejrossouw logic28 commented ·
Very nicely executed setup and I like the use of a dolly wheel "jack" as tilting adjuster for the arrays? I have limited insight on the lightening topic other than to date not personally seen any media on solar panels being struck by lightening. Just thinking out loud. DC does not have a reference to earth as with AC systems and as such, unless e.g. your RCD at the house rated for AC/DC current, feeding any back via a combined earth may actually compromise the functionality of the protective devices.
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logic28 avatar image logic28 ejrossouw commented ·

Yes, that is why I only connect the PV to ground locally in order to discharge potential extreme currents through the surge protectors.

About the jokey wheel jacks (LOL) I could not find anything readily available in the UK so I came up with this temporary solution and in the future perhaps install electric actuators automatically adjusting daily or weekly

However, in order to use these I had to apply a couple of modifications that I can share here if someone is interested; the major one being the need for a bush in which the piston runs into otherwise shaking like hell with any wind. Now I have a firm and precise adjustment.

img-20230302-163905-987-copy.jpg

Also as I'm only using one of the two arms that normally holds the wheel, I've introduced a bushed spherical joint again allowing for precision and flexibility.

All tilting framework on large bearings for good support, none of that one-bolt nonsense I've seen used by installers img-20230127-135944-935-copy.jpg

so to guarantee continuity I made four flexi-grounding conductors

img-20230711-131856-531-copy.jpg

the red compound is copper grease


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