Lets kill the guy that asked yet another ground question

The Only Sarge

Ok....my neighbors cousins wife's friend is asking about grounding his battery bank. Not me.

So he asked on a reputable forum and a Aerospace electronics engineer with 20+ years of solar installations answered...

You don't need to ground batteries. In fact, if you are using an inverter, you better NOT ground your batteries.
You need to ground:
Solar Mounting Racks
PV mounting rails (racks)
Generator, only via it's ground bolt
Inverter, only via it's ground bolt, if supplied.

What can happen, is sneak paths develop, and you can trip Ground Fault Protectors - ( AC & DC ) or blow some of the internal protection fuses in inverters.


OK...so my next door neighbors friends wife cousin is in the fetal position sucking his thumb so I thought I would ask you guys. You know...as a humanitarian gesture.

Thumb don't taste half bad....

Cariboocoot

Re: Lets kill the guy that asked yet another ground question

Mr. Aerospace Engineer ought to read the bloody instruction book that came with the inverter sometime.

In fact more people should read the instructions that come with the equipment they buy. It's amazing how much information is in there.

Remember: grounding is safety thing, not an operational thing: it does not, in the normal course of operations, carry any current. You'll never know if you did it wrong until it's too late. Unless you do something horribly wrong.

Negative connections on most charge controllers and inverters is connected to the chassis ground. In "free standing" (RV installs) mode this doesn't matter. In "cabin" mode it needs to be attached to Earth as per NEC specs for home wiring. So do the panel mounts. Thus if anything shorts out it shorts to Earth through the ground wire, and not through your body.

When you add in the AC side of things it gets tricky. There should be one and one only AC neutral to ground bond. Some MSW inverters can not take this, and they should tell you so in the aforementioned instructions.

The other part that gets tricky is the ground loop construction that can happen whenever you don't connect all the grounds to a single, common earthing point. Needing multiple earthing points due to soil conditions is another issue. Having separate ground points that are "far apart" is yet another issue. Lightning protection grounding still another.

Grounding! It's fun! It gives you headaches! It causes arguments! Whee!

The Only Sarge

Re: Lets kill the guy that asked yet another ground question

I think he is saying to ground the inverter chassis and the panel racks....and not the battery negative. Which is in conflict with what many others say.

My neighbors wife's cousin has the inverter chassis grounded and the panels...but no ground from the negative battery post to earth ground. Many tell the poor guy that he must ground the negative battery post to ground and many say DO NOT do it....as described above. Many tell him if he does not earth ground the negative battery post none of his fuses will blow. I asked him if a car can blow fuses Thus the thumb sucking began.

Me thinks this AC/DC inverter battery bank environment grounding is a fuzzy science.

Cariboocoot

Re: Lets kill the guy that asked yet another ground question

Fuses have nothing to do with it, since they aren't part of the grounding circuit but rather the normal operating circuit.

Ground is there for if things go wrong and the metal case of something might become energized, instead of the current flowing through (-). It drops the current to ground and if the Amperage is heavy enough the fuse will blow. This is why we put fuses on (+) wiring and why (-) wiring is very often connected to chassis ground in DC systems anyway. You ground the (-) battery post if that's the only ground point. If there's a separate ground lug on the case chances are it is already connected to (-) anyway.

It's like playing the lottery. Most of the time you get nothing. Sometimes you get a few Volts back. Once in a million you "hit the jackpot". That's when the proper grounding pays off.

Cars and RV sit nicely insulated from the Earth via rubber tires. If something gets energized that shouldn't there really isn't any path to ground for current to flow through. This doesn't pose a problem unless you're holding the "hot" in one hand and the "cold" in the other. Even then, 12 Volts just doesn't push much.

But you're absolutely right: when you throw in that DC/AC mixture - even the NEC is confused/confusing. Add GFCI on both AC and DC and it gets worse. Since expert engineers can't agree on this, how could we poor minions of wiring know what to do?

Like I say, chances are pretty good the (-) is already connected to chassis ground and that is earthed. No worries. You get bigger problems with the higher Voltage AC side.

RCinFLA

Re: Lets kill the guy that asked yet another ground question

I agree with both of you.

Regulations call for grounding battery neg terminal. It is a safety thing if something in inverter fails. It probably requires a permanent short to develop between inverter transformer's primary and secondary windings which in my opinion is relatively low probablity.

In S. Fla. we are in the lightning capital of the world. I don't ground my battery because I believe it just gives another path for lightning to blow out the low voltage side components of the inverter.

The Only Sarge

Re: Lets kill the guy that asked yet another ground question

OK ...he took his thumb out of his mouth and he is up....decided with all his fuses and grounded inverter chassis and panels etc...that there will be no battery negative to earth ground and we all will live to tell our Grandkids about it.

Of course we may be standing in a pile of smoking rubble as we tell the grounding story to the lil boogers.....

Frxddy

Re: Lets kill the guy that asked yet another ground question

You guys make me think too much. How can I enjoy this thumb with all this thinking going on??

SolarLurker

Re: Lets kill the guy that asked yet another ground question

Don't feel bad asking about grounding. I cannot stand when people ask questions on forums and everyone jumps all over them about asking a frequently asked question. As far as I can tell that seldom happens hear.

I have found search functions to be less helpful then people think, often older posts may not be relevant, could be old, or difficult to get the exact answer your looking for.

The Only Sarge

Re: Lets kill the guy that asked yet another ground question

My hobby is performance muscle cars. I was a Super Mod with years invested in a website that grew to over 40,000 members.

I quit this year. I cannot take the "internet mentality" that permeates with the young internet raised kids. Flaming, trolling and yes....the "Use the Search Button Nazi's". What people forget..is they also started out knowing nothing. But soon become internet experts with an "attitude"......I am making fun of that entire culture honestly and probably should not be so sensitive on this forum.

Grounds.

When I first started with my solar experiment. I had a inverter from WalMart and hooked it up to my transfer box. It was an El Cheapo Modified Sine Wave thing. The common was tied to the ground bus in my house wiring and smoked that thing

My point is this....I read till my eyeballs fell out and wired it exactly as many post all over the internet said to wire it. So what I learned is instead of just duplicating what some internet expert has done on his system may not apply to you......because there are many variables across equipment and environments that cause significant design issues. I will not pay a "expert" to come and install anything. Not in my DNA:) I put freon in my central units and work on my own cars. I will win this solar system project! And I have....of course I have some controllers/inverters "gently used" I will entertain offers for Did you know you can smoke a WattsUp Meter?

I will also say BB and the other mods do a great job of trying to express the variables found across multiple systems. I see people get frustrated and just want a plug and play answer....but our mods here do a great job of educating versus just answering some question generically or with what has worked for them on their system.

So I have fuses the correct size and placement. I was taught and provided (here) the various documents/tools to figure out my specific system design/equipment fuse/wiring requirements to make it safe.

Thanks Cariboocoot for all your education and BB for you wealth of knowledge and patience with us "Newbies"

I wonder what gets those battery acid stains off cement?:p

BB.

Re: Lets kill the guy that asked yet another ground question

A little phosphoric acid and a broom for scrubbing can work. Note that it will make the surface "non-skid"--We did this at a friend's place that had a sidewalk that was floated too smooth (and slippery in wet weather). If this is an interior garage floor--I would not do it.

Regarding searches--Yes, we try not to answer "use the search button"--If you don't know anything about the subject, how would somebody know what to search for (common terms, etc.).

However, I do have a hint that works well. If you know the website you want to search--Use google with the "site:" tag... For example:

• msw inverter grounding site:wind-sun.com

Will use Google's natural language search, "fuzzy" matches, and limit them to the forum.

A couple threads about Lightning:

Off Grid Grounding Technique?
Another Question, this time about Lightning

Note, the above are discussions, not a do A, B, and C--and you will be "safe". There probably is no such thing with lightning. Several different techniques are discussed--and a few of those posters even have experience with lightning. :cool:

And our host's consolidated FAQ page:

www.windsun.com
Lightning Protection for PV Systems

From other past posts here, Windsun (admin/owner of NAWS), he said that most of lighting induced failures he saw were in the Inverters' AC output section.

Towards the end of this thread is a very nice discussion of proper generator grounding.

-Bill

JESSICA

Re: Lets kill the guy that asked yet another ground question

Before I start, please keep in mind 3 things: 1) English is not my first language; 2) My formal education is in Humanities, not in Electricity; 3) As my niece says, I am dumb.

So I have to ask, after reading this thread several times, Is the following interpretation/conclusion right?

I have to ground my panels frames, via a 6 or 4 awg attached to a copper ground rod inserted 10 feet in the ground/soil;
I have to attach to THE SAME ROD ALL the following ground cables/wires:

a cable from the chasis of my mx60 controller;
one from the negative post of my battery bank;
one from the chasis of my inverter;
another one from the negative terminal of my inverter;

Is that right?

More important (in my situation): Can/should I use THE SAME GROUND ROD I have in the ground for lightning protection, the one that is attached (now) via # 4 bare copper wire, to another rod in the roof?

Thanks for your patience! I need straight and simple answers!

mike95490

Re: Lets kill the guy that asked yet another ground question

JESSICA wrote: »

...................
I need straight and simple answers!

Don't we all !

But the inspector at my install wanted a ground rod at the inverters AC panel. And my array and pole and mounts, are in a 24"di, 10' long concrete hole in the dirt. Now I have 2 ground points. 400' up the hill , my 240VAC pump is in the pond. (ground #3) Another 500' up, is my ozone generator, which needs ground # 4. 250' across the creek, is the sub panel for my house, with ground #5. And 100' from that, will be the house, and I'm sure another inspector will want a ground rod #6 at it's panel.

And my question is, do I ground the seamless metal roof ?

Cariboocoot

Re: Lets kill the guy that asked yet another ground question

JESSICA wrote: »

Before I start, please keep in mind 3 things: 1) English is not my first language; 2) My formal education is in Humanities, not in Electricity; 3) As my niece says, I am dumb.

So I have to ask, after reading this thread several times, Is the following interpretation/conclusion right?

I have to ground my panels frames, via a 6 or 4 awg attached to a copper ground rod inserted 10 feet in the ground/soil;
I have to attach to THE SAME ROD ALL the following ground cables/wires:

a cable from the chasis of my mx60 controller;
one from the negative post of my battery bank;
one from the chasis of my inverter;
another one from the negative terminal of my inverter;

Is that right?

Yes, just about. Except it's debatable as to whether you need to ground the (-) battery post. Pretty sure the MX60's case is attached to negative (my memory is failing) and possibly the inverter as well. So one wire running from the panel mounts and connecting to the case/chassis of the controller and inverter will probably pick up the (-) wiring as well and ground the whole DC side of things. This should go to the same ground rod as the AC ground. The thing to watch out for here is the AC neutral-ground bond which does instant bad things if your inverter is MSW type.

More important (in my situation): Can/should I use THE SAME GROUND ROD I have in the ground for lightning protection, the one that is attached (now) via # 4 bare copper wire, to another rod in the roof?

Thanks for your patience! I need straight and simple answers!

In my opinion grounding for lightning rods should be separate from system ground. Lightning arrestors (that attach to other wiring to sink any ambient high Voltage/frequency) can attached to the system grounding rod. Preferably the lightning rod ground and the system ground will be on opposite sides of the house, just in case things get a bit energized.

You are not dumb; this is one of the most complex issues in electricity and many experts don't agree on what should be done.

BTW, I'm no expert. But I do live in a high lightning area (where we watch the forests burn every year) and have seen lightning do some incredible things over the many years that I've surprisingly failed to electrocute myself while messing about with all sorts of wiring. Must be doing something right, eh?

Cariboocoot

Re: Lets kill the guy that asked yet another ground question

mike90045 wrote: »

Don't we all !

But the inspector at my install wanted a ground rod at the inverters AC panel. And my array and pole and mounts, are in a 24"di, 10' long concrete hole in the dirt. Now I have 2 ground points. 400' up the hill , my 240VAC pump is in the pond. (ground #3) Another 500' up, is my ozone generator, which needs ground # 4. 250' across the creek, is the sub panel for my house, with ground #5. And 100' from that, will be the house, and I'm sure another inspector will want a ground rod #6 at it's panel.

And my question is, do I ground the seamless metal roof ?

You know I think having separate ground rods hundreds of feet apart is acceptable. Like the difference between yours and your neighbour's house.

As for the roof ... I'd be inclined not to ground it. Although I can understand why some would suggest to do so. Is that answer ambiguous enough, or should I elaborate and make it more nebulous?

BB.

Re: Lets kill the guy that asked yet another ground question

JESSICA wrote: »

I have to ground my panels frames, via a 6 or 4 awg attached to a copper ground rod inserted 10 feet in the ground/soil;
I have to attach to THE SAME ROD ALL the following ground cables/wires:

1. a cable from the chassis of my mx60 controller;
2. one from the negative post of my battery bank;
3. one from the chassis of my inverter;
4. another one from the negative terminal of my inverter;

Note that #2 and #4 create a "ground loop". A picture of this would look like:

[FONT=Fixedsys]

Battery Negative=================Inverter Negative
                 |             [COLOR=Red]|[/COLOR] 
                 |             [COLOR=Red]|[/COLOR]
                 -------[COLOR=Red]--------[/COLOR]
                       |
           Ground Rod
[/FONT]

The "RED" portion above is what creates a "ground loop"--a parallel path for current to flow between the inverter and the battery. And, depending on the current involved, you could cause problems (i.e., your inverter can send 200 amps down your very heavy battery cables, but you are only using 6 awg wire for grounding--you may over heat the ground cable.

So, don't do #4.

Regarding the grounding of the Outback charge controller--it is probably OK--but always read the manual. The MX has a separate grounding lug attached to the chassis that (I don't believe) is attached to the battery negative terminal.

More important (in my situation): Can/should I use THE SAME GROUND ROD I have in the ground for lightning protection, the one that is attached (now) via # 4 bare copper wire, to another rod in the roof?

Lightning is not "simple". It flows according to a different set of laws (AC/high frequency rules--basically radio frequencies). So, having rounded/large diameter bends (not square corners, but something like > 18" diameter--if I remember correctly).

In some ways, it is like water flowing through a pipe... Nice rounded bends, the water flows without turbulence. A sharp 90 degree square bend, there is turbulence--and with lightning, it will find a different path to follow.

And, because of this (plus the high current, and the fact that ground and wires do not carry radio frequency energy very well) how close or far apart things are makes a difference too... If all of your major ground bond connections can be made within 10' or so of the ground (AC mains, battery bank ground, charge controller ground, etc.)--then sending them all to one rod is fine.

If your AC/earth ground rod is one end of the home, and 50' away is your solar equipment--then running all of the wire to the far ground rod may not be the best choice.

Here, drive a second ground rod near the solar equipment for your DC and Array Frame Grounds.

Personally, I would also connect this second ground rod to the closest metal water pipe (if you use metal water pipes in your home) too. And, if possible, I would run a 6 awg or heavier ground wire from the 2nd rod back to the first ground rod (although, I could understand if others here with more knowledge would disagree with this suggestion).

If I recall correctly, you have an MSW inverter, so do not ground reference your AC output (i.e., ground the neutral wire) at the MSW inverter (unless the manual tells you it is OK/Recommended--MSW inverters typically will get a "dead short" if the battery negative and MSW Inverter AC output are grounded together).

-Bill

BB.

Re: Lets kill the guy that asked yet another ground question

I think the answer is that if you have lightning in your area--You should run a lightning system (rods and connections) on any roof top--not just metal. The idea being to get the energy to flow through a known path (lightning rods/cables) instead of incidental paths (roofing, plumbing vents, down spouts around the building)...

Although, in one of the links above, they do say that even metal down spouts should be placed at the corners of buildings (or opposite each other if a round building) to optimize current flow (lightning, being Radio Frequency Energy wants to "spread out from the center"--aka the "skin effect"). Down spout placement is the same recommendations as for grounding cables too.

-Bill

JESSICA

Re: Lets kill the guy that asked yet another ground question

BB. wrote: »

Regarding the grounding of the Outback charge controller--it is probably OK--but always read the manual. The MX has a separate grounding lug attached to the chassis that (I don't believe) is attached to the battery negative terminal.

Here, drive a second ground rod near the solar equipment for your DC and Array Frame Grounds.

Personally, I would also connect this second ground rod to the closest metal water pipe (if you use metal water pipes in your home) too. And, if possible, I would run a 6 awg or heavier ground wire from the 2nd rod back to the first ground rod (although, I could understand if others here with more knowledge would disagree with this suggestion).

If I recall correctly, you have an MSW inverter, so do not ground reference your AC output (i.e., ground the neutral wire) at the MSW inverter (unless the manual tells you it is OK/Recommended--MSW inverters typically will get a "dead short" if the battery negative and MSW Inverter AC output are grounded together).

-Bill

Cariboocoot:

Thanks for saying "You are not dumb"; I will show this to my niece!

Bill: Water pipe, from the street to my house, is pvc. So, no can do. Yes, msw inverter (the old loaner yet!), but a new tsw is in agenda, possibly another Exeltech, or a Samlex. Hope this time no roaches nor lightning destroy it!

Right now, my grounding seems to be perfect, as per what both of you have written. I got confused about the necessity of grounding the negative terminal of the battery and what Cariboocoot wrotte regarding "just one common ground". But I do have two different rods, maybe 40' apart, one for all the aforesaid stuff and another one only for the lightning rod.

As usual, THANKS for all the help.

ggunn

Re: Lets kill the guy that asked yet another ground question

Cariboocoot wrote: »

Negative connections on most ... inverters is connected to the chassis ground.

True, but that connection is usually through a GFI fuse or breaker, which is why you don't externally ground the negative of your PV array, else you will defeat the GFI.