New install questions

Re: New install questions

gww1 wrote: »

Bill
I spent a little time drawing a basic paint diagram of how I was talking of wiring my system but then couldn't get it to load so I gave up. I did read all your links that you posted for me. Just made me feel like a bigger idiot. You posted.
...
I don't think I am doing well with the discussion part and need an A, B and C-- and I will be as safe as that will make me. I will get as close as I can and then quit worrying.

Grounding is a pretty complex subject and subject to various theories on how best to implement lightning and safety measures. Doing this in writing, remotely, and with somebody who knows just enough to get into deep trouble...

Remember, I am neither a licensed electrician, an expert in lightning control, or at your site--Best I can do is, hopefully, give you some information and links to follow up on and/or get some local/expert help. If you know any HAMs (amateur radio folks)--You can get some good help from them.

The things that screw me up are;
1. The outback drawing shows a ground at the pv and nothing from the combiner going to the house. A separate ground goes from the batteries to the inverter to the ac main panel.

A very good lightning ground system would be to ground the array and mounting to a local ground rod.

Ideally, run the lightning ground among the framework and the mounting directly to the ground rod. I would not run the lightning ground from the array through the combiner box to ground (that is "bringing" the lightning energy very close to your DC connection lugs--There is no reason, in my mind, for doing that.

Just run a separate 6 awg ground from the local rod to the combiner box ground connection.

The link you provided:

http://lib.store.yahoo.net/lib/wind-sun/PVcombiners-explained.pdf

Shows the array frame grounds going to the safety ground bus inside the combiner box... I would (as I said earlier) run the safety ground wires directly the array ground rod. I do not see a good reason to bring the lighting induced current anywhere close to the DC power connections if I did not have to do that.

That would be the "end" of the array lightning ground discussion.

My suggestion of running a 6 awg wire from the array ground rod back to the house main ground rod--That is for providing an AC/DC electrical bond between the Array and the Home Power Station grounds. It is possible to energize structures so that you have different voltage levels 100' apart. I personally like to bond the out structures with the "same ground" as the source of the power (i.e., home power--whether AC or DC, locally generated or power lines from a utility). This will not help with lightning, but can help reduce the chance of shock between a power tool using power from your home around the solar array structure (i.e., a three wire power metal electrical drill working on the metal framework with a "different" ground potential).

It is not a common problem--But there can be voltage gradients in the earth. For example, electrical power pylons can have leakage current (dirty insulator, etc.) that can "energize the local earth". There have been cases where cattle have been killed by standing near a pylon (for humans, our feet are close together and power goes up one leg and down the other. For cattle, their legs are far apart and current can flow up the front legs, through the heart and back down the rear legs and kill them).

If you do not, for example, run AC power from your home to the solar array structure (shed near by, yard lights mounted to frame work, an "extra AC outlet" for back yard lighting/music/etc... Then the linking of the remote and main ground is probably not necessary (I am not doing this based on code, just based on safety concerns that I have).

2. The combiner wiring drawing goes; The combiner wiring ground shows from the pv to the combiner to the inverter to the main ac panel with no ground rod at the pvc. I believe this fits the new nec rule to the minimum.

The Midnite document (above link) talks about grounding as "Safety Ground"... Basically just running wires from outlets/branch circuits in the home to a common ground bus bar, then back to the main panel/earth ground rod. That is perfectly good for a "safety ground".

With lightning, it is "RF Energy" (Radio Frequency Energy). The energy does not follow "copper wire"--It also is affected by the inductance and capacitance of the cabling (which is frequency dependent).

More or less, while 60 Hz energy follows the wiring through the home wiring, Lightning energy moves to the "outside" of the structure (magnetic repulsion pushes the current away from the center--this happens with 60 Hz AC current too--But the effect is less much less than an inch--skin effect).

When grounding against lightning strikes, say you have two cables going to lightning rods on the roof. The two cables should be at opposite sides/corners of the home/grain silo/etc. (as far apart as possible). That is how lightning wants to flow. Running 6 awg cable into a metal box--Not real likely to follow just that route.

3. You seem to be saying that, above minimum, the pv should have a ground rod that goes through the system to the ac panel which ends up at the house ground rod. Am I getting the wrong ideal here and would the sequence be from the pv frames to the ground rod to the combiner to the house?

NO. I am not saying that.

Solar Panel Frames->grounding cable->local ground rod
AC Main Panel Earth/Safety Bond->another grounding cable->main panel grounding rod
AC Main Panel Neutral Wire (north America)->Earth/Safety Bond bus block in main panel (*see note)
Water Pipes/gas pipes in home/etc.->yet another grounding cable->main panel grounding rod
DC Ground Bus (negative Battery post, etc.)->and yet another grnd cable->main panel grounding rod
Solar panel local grnd rod -> XYZ feet of 6 awg cable -> main panel grnd rod (optional)

I need it short and sweet cause there seem to be conflicts that I am having a hard time picking through.

So:

• Solar Panel Frames direct to array ground rod. (lightning control)
• Combiner box earth/safety Ground to array ground rod. (lightning control). Do not connect the solar array negative wiring to the safety ground bus--Just to the insulated bus bar).
• Battery Bank Negative Lead to building ground rod (safety ground for DC and AC shorts, some lightning suppression too)
• OPTIONAL: 6 awg cable from Array Ground Rod to Building Ground Rod
• IF YOU HAVE GRID POWER: Your AC Neutral will be tied to Earth/Safety Ground in the Main Panel.
• IF YOU DO NOT HAVE GRID POWER AND A MSW INVERTER: You will want to "float" AC White Wire--Do not attach to Safety Ground.

If it works reasonably well I don't worry to much after it is done. I don't want to do something that is so blatantly stupid that someone can call me on it and be right.

If this was an RV (for example) where you sometimes have power from an RV park, and a local inverter, and a local AC generator--Then we need to talk about Neutral bonding/grounding some more.

If I add a ground rod at the pv do I have to worry about the impedance matching the house rod?

Not that I can think of--There is a ground rod test (special equipment)--But I have never been involved in this--That would be your electrician that would determine if your ground rod is "good enough" (dry earth, frozen earth, rocky ground, etc. can be very difficult to get a "functional ground" connection between rod and earth).

I know you like the ground rod at the panels I just need to know the two points it hooks at to keep it a safe thing and not a bigger hazard.

I believe that the usual install is to run an "S" of cable through each panel ground clamp (and major structure connection) directly to the array ground rod (NEC requires a single unbroken wire--You are not supposed to splice ground wires). I would believe it is OK to break a run into two or more runs of copper (i.e., 4 panel frames to ground rod, another 4 panel frames to ground rod, etc. if that works better).

I can't believe I can read that many post and can still be confused. I am sorry, can you try one more time, PLEASE?
Thanks
gww

And anyone with more experience than I--Please jump in... I am a bit out of my depth here.

Should I run the ground from the pv frames to the combiner box to the ground rod at the pv then strait to the house ground rod...

and have the inverter side connected to the ac panel ground buss bar? This means that the pv ground rod takes a different route to the house ground bar then the inverter and batteries? have I got it yet?[/QUOTE]

Lightning Ground Cable should run directly from the frames, down the side of the structure/outside of home, etc. to the closest earth, then drive your ground rod there and connect the ground cable. No extra jogging this way or that way if you can avoid it. Lightning current should go to earth the shortest path possible... Running wire 40' along the side of the house to a different patch of earth won't cut it. The Lightning will want to leave the wire and seek ground through another path (wire/conduit in wall, etc.).

Personally, I would run a separate ground wire from the combiner box to the array ground rod (or house ground rod, or even a ground rod driven under the combiner box--depends on where the combiner box is installed). Remember, lightning ground should be short and straight down to earth. If combiner box is on south wall and AC panel ground is on the north wall--Drive a ground rod on the south wall under the combiner box (technically, combiner box on side of your home, I think you would have to run a ground wire from the AC main panel ground rod to the new combiner box ground rod--The combiner ground rod takes care of lightning current, the 6 awg back to main panel ground rod takes care of AC and DC currents in the event of a short circuit).

...and have the inverter side connected to the ac panel ground buss bar? This means that the pv ground rod takes a different route to the house ground bar then the inverter and batteries? have I got it yet?

You lost me here...

We have not really discussed inverter grounding yet (other than the MSW inverter output neutral bonding warning above).

Before we talk about this--Let us make sure you agree/understand with what I have said so far.

TSW/MSW Inverter/AC Mains/Generator neutral bonding is a whole 'nother set of worms.

-Bill

Re: New install questions

I will add a link to this thread:

Panel Fire Question

This was actually a contractor installed/city inspected system. Even if you try to do things "right"--You can still get blindsided.

-Bill