Grounding my off grid RV system

Plowman

BB. wrote: »

The system will work fine ungrounded...

Primarily to protect against short circuits (battery + to metal sink, electrical conduit, etc.) and lightning/static charges (solar panels on a roof can pick up several hundred volts of charge from the natural electric field of the earth).

Portable/small systems are generally not grounded. Permanent systems (cabins/homes) are generally grounded.

For vehicles, generally the battery negative is grounded to the metal chassis.

Grounding can be a very complex subject--And grounding connections can get complicated too.

-Bill

BB, grounding has confused the heck out of me. Right now I only have one 158W panel connected to two Trojan T-105s, but hoping to get 2 or 3 more of the same panels soon. Charge controller is a Morningstar TS-45. It's ungrounded now, any reason to ground it after I expand? Everything is mounted on/in a small metal cargo trailer 100 feet from my RV.

BB.

Re: Grounding my off grid RV system

Plowman,

I moved this to your own thread... Hopefully it will keep things a bit easier to follow.

Where is your AC inverter (if any) and battery bank? At the remote trailer or the RV?

Do you have a lightning in the area (reasonable chance of a strike)?

Is the RV permanent or mobile? Would you setup a Electrical Box to plug in the RV when parked? Are you planning to (or do you already) have the capability to run solar+battery+AC inverter in the RV now?

-Bill

Plowman

Re: Grounding my off grid RV system

Thanks BB, I was confused where my post went.

Inverter is in the cargo trailer with the batts, charge controller, etc. It's a tiny little thing, 150W Sima, but I also have a 400W Cobra as a back up. I'm just running an extension cord (100' 12/3) from the inverter to the RV, which is situated in the shade so I don't have to run the AC in summer. I'm drawing roughly 20-25 ah per day from the batts (based on meter between batts and inverter).

RV is stationary, as is the cargo trailer.

Lightning is pretty minimal in my area.

I'm off-grid right now, currently using the Dmsolar 158W panel and two T-105s, supplemented with a Honda EB3500 generator and Iota 45 amp charger. Plan is to expand to 3 panels, which is about right for the two T-105s I think. I can fit 4 panels on the cargo trailer, but they come in two-packs and money is tight, so it makes more sense just to buy two right now.

Specs on panel:
* Pmax: 158W
* Vmp: 18.9V
* Imp: 8.47A
* Voc: 22.7V
* Isc: 8.76A

Pic of cargo trailer (I'm going to rebuild the mount and situate the panels vertically):

BB.

Re: Grounding my off grid RV system

I would drive a ground rod (or bury a ground plate--easier to move when needed)--And run a 6 awg minimum cable from the array frames, to the trailer frame to the ground plate.

I would also ground the DC Battery bus to the trailer frame/ground plate too (lightning and DC short circuit protection).

It is not "needed" for day to day operation, but that looks pretty exposed--If there is any chance if a lightning strike, I would rather be safe than sorry (if you are talking about years of residence at the location).

AC grounding... A bit more difficult. At the RV, I would suggest grounding the AC neutral and trailer frame to a local ground rod/plate (Lightning protection). But this gets more difficult and complicated.

If you have a MSW AC inverter, you should not ground the neutral (there is "no neutral" with most MSW type inverters). Also, the generator is just about the limit where Honda may or may not have a neutral bond at the genset.

Also, if you have any GFI breakers/outlets at the inverter/genset--You cannot run a neutral-Earth bond. It would probably trip the GFI devices.

This is all about lightning protection (from my point of view)... If you truly do not get strikes in the area--Then the suggested grounding is probably overkill.

If you move the RV during the year (RV parks, campgrounds with AC power, bring your genset with you)--You might want to look at installing a lightning surge suppressor on the AC inlet to your RV.

http://www.solar-electric.com/suprde.html

It would not hurt. And gives you better protection both at home and on the road.

-Bill

Plowman

Re: Grounding my off grid RV system

Thanks BB. Is lightning the primary (only?) reason to ground a small system like this? My part of western Oregon has one of the lowest levels of lightning in the country according to this map, probably similar to San Fran. It's rare, but it does happen every once in a while.

There are a lot of tall trees nearby, I live/work on a tree nursery, so there's no shortage of the damn things . I had to cut down a 15+ foot cedar that would have shaded the panel, but there's still a row of them to the south of it.

If I were to ground the trailer like you describe, would it prevent a surge from traveling through the 100' extension cord that runs to my RV? I'm not sure how I'd ground my inverter, it's just a little car type inverter (150W with cigarette plug), don't think it has any capacity for grounding.

My generator does have a grounding lug on it, and I believe the Iota can be grounded as well but would have to check on that.

niel

Re: Grounding my off grid RV system

i'll answer this.

no, it isn't the only reason as there could be noise, static charges, and rogue voltage buildups in relation to ground.

the wire can be protected to some extent using an spd and that does mean a ground rod or screen in place for it to work.

Plowman

Re: Grounding my off grid RV system

niel wrote: »

i'll answer this.

no, it isn't the only reason as there could be noise, static charges, and rogue voltage buildups in relation to ground.

the wire can be protected to some extent using an spd and that does mean a ground rod or screen in place for it to work.

OK, so you guys have convinced me I should definitely ground at least the DC side of it. Grounding is new to me, only grounding I've done is with an electric fence. Don't suppose you can point me towards a website that describes the wiring in greater detail? I've spent a lot of timing googling grounding and have come away more confused than when I started.

I'm imagining wires connected to all the panel frames (can I just bolt it directly using a ring terminal or do I have to buy a special lug?), which run to a ground bus bar (like this) in the combiner box, which runs to the trailer frame (using another ground bus bar?), which runs to the ground rod. Plus another wire from the charge controller that runs to the same spot on the trailer frame. Plus maybe one from the generator.

How about the batteries? BB said to ground it using the bus (negative I assume?), but I don't have a bus, everything's connected directly to the battery terminals using ring terminals.

Does the ground wire have to be uninsulated copper or can you use insulated stranded copper wire? What size? BB you said 6 AWG, but is this for everything or can I get away with smaller wire in some places?

And is one ground rod (or plate) sufficient? At the old farm I used to work at I believe we had three ground rods for a rather large deer fence.

unseenone

Re: Grounding my off grid RV system

You should be able to pick up the required components at a hardware store, such as Home Depot, Lowes, etc. A standard 8' ground rod is cheap less than 20 bucks, the plates are expensive. I will leave the technical aspect of grounding the frames to the experts here. Just remember, short, direct, no sharp bends is the general rule.

boonhauler

Re: Grounding my off grid RV system

BB. wrote: »

I would drive a ground rod (or bury a ground plate--easier to move when needed)--And run a 6 awg minimum cable from the array frames, to the trailer frame to the ground plate.

I would also ground the DC Battery bus to the trailer frame/ground plate too (lightning and DC short circuit protection).

-Bill

Bill, I have never heard of a "Ground Plate" before. Mobile grounding is an issue I would like to do more research on.

Anyone have any idea on where I can find more info?

Thanks, Cee

BB.

Re: Grounding my off grid RV system

I have not found much on ground plates:

http://www.kuefler-lightning.com/series700-ground-rods.htm

Grounding plates are used when a typical ground rod (typically 10’ in length) is unable to be driven into the ground (i.e, rocky ground and etc.). Grounding plates come in typical sizes with mechanical cable attachments or with exothermic cable connections, however, if you require a specific size of grounding plate any size is available with 2 square feet being the minimum.

And another vendor:

http://www.tlpinc.com/products/grounding/ground-plates.html

From an RF point of view--A 10' long "skinny ground rod" has much higher impedance (complex resistance--i.e., inductance) than a flat plate (lightning being a "higher frequency" wave form, not a simple DC current--Approximately 7kHz maximum frequency--Not much energy above that frequency, as I recall).

If you can bury a plate in otherwise good soil, it should work better than a 10' ground rod (in my humble opinion). Also, much easier to move around/bury in rocky soil, etc.

This is a nice article written by/for a HAM Radio station--But much of the information applies to homes too (AC wiring, etc.). Note the article was (I think) written by a native French speaker--But it is still very readable and interesting.

http://www.astrosurf.com/luxorion/qsl-lightning-protection.htm

-Bill

niel

Re: Grounding my off grid RV system

plowman,
grounding can get complicated to explain everything. you can put in 1 rod or plate if buried, but don't go overboard as you can go nuts with this. i did so i know. going further doesn't hurt, but in addition to what i say below please put a surge protection device on the pv + and - as the wires can pick up that energy just like a transformer and send a surge down to the equipment further downstream. if no spd is bought then at a minimum buy at least 2 mov's to go from + to ground and - to ground. not sure if radio shack would still carry these and most electrical outlets do not carry them, but some electronic parts stores do carry them and are not terribly expensive.

#6 is a good size of wire to use, but i believe the nec allows to #8 if copper. this is ok in some cases, but you have to think a bit like lightning to use heavier wiring in more critical places that it's apt to flow though. this is a guessing game to a degree as lightning does what it wants to. do remember that even #6 is insufficient for handling a full strike and even bigger wire is better, but one can go nuts here too. i would not skimp on the wire size for the pv frame or trailer frame to ground so go thick there. do not daisy chain the pv frame ground wire to the trailer as this should be a continuous wire straight to the ground rod. straight is literal if you can get it, but if you have to put bends in the wire then make it a gradual circular turn as lightning is more apt to jump off of a 90 degree turn.

as to the wire being insulated, it doesn't matter from an electrical standpoint, but the nec likes either bare wire or wire with a green jacket. imo, it doesn't matter about if insulated or not and it doesn't have to be solid wire either as it can be stranded. in fact stranded is often the better choice as the wire will act better on the higher frequencies of lightning and give it a bit more flexibility from breakage.

almost forgot to say to keep the wires as short as possible and place the rod or plate as close as possible to the wires.

jonr

Re: Grounding my off grid RV system

I believe that grounding straps (ie, strips of solid copper sheet) are the best choice.

Keeping lightning surges out of everything else is hard, but I'd use more than just movs. Ie, some inductance (maybe just a couple loops in the wires?) and some TVS diodes.

boonhauler

Re: Grounding my off grid RV system

niel wrote: »

if no spd is bought then at a minimum buy at least 2 mov's to go from + to ground and - to ground. not sure if radio shack would still carry these and most electrical outlets do not carry them, but some electronic parts stores do carry them and are not terribly expensive.

Okay, I get what "SPD" means but have no idea of what "MOV's stands for. Can you help us non-techies out a little? A link maybe?

Cariboocoot

Re: Grounding my off grid RV system

boonhauler wrote: »

Okay, I get what "SPD" means but have no idea of what "MOV's stands for. Can you help us non-techies out a little? A link maybe?

Metal Oxide Varistor. http://en.wikipedia.org/wiki/Varistor

boonhauler

Re: Grounding my off grid RV system

BB. wrote: »

If you can bury a plate in otherwise good soil, it should work better than a 10' ground rod (in my humble opinion). Also, much easier to move around/bury in rocky soil, etc.
-Bill

Bill:

Once again, Thanks for the links and Info. So, do you have any idea of what the burial requirments are?

I was hoping to ground the solar panels, charge controller, Inverter, and the A/C system........should the D/C system be as well?

Can all these systems share a ground?

SmartGuage use to have a page discussing this issue but it's been changed to just info for Boaters.

Again, I'm mobile off-grid and there ain't no pedestals around to hookup to where I'm going!

Cariboocoot

Re: Grounding my off grid RV system

boonhauler wrote: »

Bill:

Once again, Thanks for the links and Info. So, do you have any idea of what the burial requirments are?

I was hoping to ground the solar panels, charge controller, Inverter, and the A/C system........should the D/C system be as well?

Can all these systems share a ground?

SmartGuage use to have a page discussing this issue but it's been changed to just info for Boaters.

Again, I'm mobile off-grid and there ain't no pedestals around to hookup to where I'm going!

Panels, controller, inverter input are the DC system. ESG on metal cases & frames, negative tied to ground rod. Yes, it should all be the one single ground rod.

Actually burial depth depends on local soil conditions. Most places require a minimum 5' rod and use 8 to 10 footers. Plates need to go down to damp-when-dry soil. Worst case is sandy/rocky soil which reduces ground contact considerably.

BB.

Re: Grounding my off grid RV system

Usually you want the ground to all share the same single ground point (electrically speaking).

This prevents a voltage differential between the various systems.

What you don't want is parallel grounding paths. You may have 10 amps in your AC system and 100 amps in your DC side. That is why you try to make single point ground connections. That way there cannot be a mix of current flow in the "ground" cables.

-Bill

niel

Re: Grounding my off grid RV system

boonhauler wrote: »

Okay, I get what "SPD" means but have no idea of what "MOV's stands for. Can you help us non-techies out a little? A link maybe?

as was said it is a metal oxide varistor. this is what is in the midnite spd, but it has many of them and an led indicator light on functionality and casing suitable for epanel and other electric box openings.

http://en.wikipedia.org/wiki/Varistor

http://www.midnightsolar.com/

http://www.radioshack.com/product/index.jsp?productId=2062574