Grounding question - what would you do ?

[dacflyer]

ok, i been trying to consult a few places and the NEC, but the answers are vauge.
as you all know i am working on my solar for my house, i also have lightning rods on the roof as well. and the lightning ground cable runs all across the roof, and the cable is as close as 12" to one of the set of panels.
now NEC says the panels have to be grounded, well they are.. it does not say they have to be strictly grounded on a seperate ground, but even if i was to do that, then i'd be concerned of flash over if there was ever a strike, i belive that would be rare if ever, because theres trees, power poles and a large metal wharehouse near my house.
so i think i am being smart to stay my panels grounded to the lightinig rod system..
the few electricians i talked to say they belive is fine, the system is grounded on both ends of the house, and my equipment is grounded seperatly on 2 - 10 ft ground rods tied together.
both are bonded via cad-weld ( thermalweld - thermite )
as far as i figgure, if i ever get a direct strike,and with or with out seperate grounds and / or a flashover, the panels would be toast anyway..but the equipment being on a seperate ground, it might survive.

any comments ? or some other place to ask ? maybe theres a lightning institute / lab ??

[MrAl]

Hi there,


I found these links which look pretty interesting:

http://rainmaster.com/lightning.htm

http://www.lightningsafety.com/nlsi_lhm/rtaf3.html


This is interesting because there is no normal gauge wire that can handle the high current of a direct lightning strike.

[haklesup]

I would connect the ground lead from the panels to one of the ground rods near the rod not some arbitrary place along the lightning discharge wire.

While a ground wire is at ground potential when it is quiescent, just sitting there. when lightning is striking and 100s of Amps are running through it, the potential along the wire can be quite large, even the two ground rods could be several kV difference for a split second. Lightning will do what it wants to do. lightning arrestors don't always prevent property damage but can sure help to limit it.

Make sure to update your home insurance policy with the higher value of the solar array or it may not be covered adequately.

From your other posts about Grid Tie, I assume you were all properly permitted etc. (else I assume you would not have gotten permission from the power company) does the city inspector have a comment. Several times I called my inspector to ask what he wanted to see with respect to certain things, they can be quite helpful.

[Bob Scott]

Lightning will do what it wants to do. lightning arrestors don't always prevent property damage but can sure help to limit it.

I wouldn't be running ground wires over the roof. If they start conducting massive lightning current, they lead the lightning on that path. Even after the wires have vaporized, the air around them will continue conducting lightning current in the ionized air, because ionized air is a better conductor than normal air. I wouldn't want your roof shingles to catch fire. Is there any chance you could erect very tall masts for the rods a few feet away from the house but much higher?

Lightning is strange. When I was a kid, our neighbor had a big tree that was hit by lightning 5 times in 10 years. It was the only thing within a mile that was ever struck by lightning. There was speculation that the ground under that tree was somehow special and maybe had a lot of minerals. Do you have any trees?

[haklesup]

NEC wasn't written to protect property though it is a compatible goal. It was written to protect human life. The way I see it, if your panel suffers a direct strike, something might turn into toast but at least the lightning won't be directed into the house if the structural frame of the panel is earth grounded.

[dacflyer]

yes i do have treea around the outside of my property. a big oak and many tall pines. i been living there since 94' never had a direct strike near by.

the lightning rod cable is made up of a special very thick braided cable,with thick wires. the cable is about 1/2" thick.

i think i will seek the advice of the inspector, the solar consultant i spoke with said it should be just fine just as long as its a real ground connection.

and ya, i agree..lightning will do as it pleases, so if things go boom. at least the most of it goes to ground...i have yet to see lightning vaporise a lightning rod ground cable..same with the copper wire that runs down utility poles..but, i have seen it heavily dammage 2" wide copper strapping that was used on a traffic camera pole..lol

[Bob Scott]

I was just thinking that lightning rods used to be installed on barns and farm buildings, but late in the 20th century it seems that lightning rods became out of vogue on newer buildings because the rods tend to attract lightning. Possibly TV antenna masts did the same job. I speculate.

So, you can leave the rods on the house but also install a tower "away from but near" the house with a higher rod, so as to be the preferred target for lightning. If that is too ugly, you could install some heavy and well grounded uninsulated wire up high in a nearby taller-than-the-house tree.

[dacflyer]

here in raleigh nc, there was several condos and town houses that caught fire last year, lightining rods would have saved them, there may still have been damage, but risk of fire would be almost none.
they worked in the old days on everything.. in europe they are mandatory on any building. even on bus stops..lol its true you canget them in designer styles, but they are all still effective, if installed right.

around my house, i think they weren't really needed, but as said earlier lightning does as it pleases. last week a lady and her baby were struck by lightning in front of TJ MAX store, pleanty of metal on the roof and lamp poles. but the lightning choose her and her umbrella.
she was a solidger in the army, and luckly there were 2 others near by that gave her CPR, she and the kid had bad burns, and she was not breathing and her heart was beating crazy. the cpr saved her.
i have trees and power poles around the house as well as the metal wharehouse next to me, i am still gonna keep the rods, just in case..

[frhrwa]

great information in these posts.. I just got hit by lightening last month.. my shop is metal, taller than my house by 10'.. my flagpole is metal and taller than both house and shop.. both are less than 150' from the house.. the peak of the roof on the house is 8' higher than the point of entry.. like you said, "lightening basically does whatever lightning wants".. well, it came through my bedroom ceiling right directly above me.. 1:15 AM.. hit my ceiling fan, exploded hot metal all over me, blew out my front window, set the house on fire, needless to say, blew me out of bed, blew my left ear drum and luckily I was laying on my right side, so it only got half the hearing on the right side.. blinded me for about 10 minutes.. It didn't do much to the AC wiring other than what the fire did.. tripping breakers.. it went down the low voltage wiring, smoked the co-ax, speaker wires, computer LAN wiring, telephone wiring, surround system, security system.. blew out everything attached to these, traveled down the telephone cable to the shop, smoked the brinks alarm system there.. nearly blew the metal box out of the garage with all the low voltage wiring and brinks system in it.. nothing left of that stuff except black molten material.. so... I'm rebuilding the house that I had just finished the day before the hit.. litterally painted the very last outside door, went to bed, not knowing I would be starting all over the next day.. so... with that said, I'm all ears for the best lightning rods I can find.. thanks.. wayne (deer park, WA)..

[dacflyer]

sounds like you had a direct hit..:O

i have seen some places now erect remote poles just for lightning diversion..
most have been wooden utility poles about 60ft+ and a large lightning rod attached to the top of it and heavy copper down the pole, and then a deep ground rod..possibly multiple ground rods.
there is one location here that has 6 of them around a church with a tall steeple.
the closest pole is about 50 ft away..
1st time i saw them , i thought they were erecting antennas. apon closer inspection they were indeed lightning rods..

check out the pictures etc at the Deutsches Meuseum in Germany..i been there a few times,, very LOUD and AWSOME !

http://www.deutsches-museum.de/en/exhib ... ge-test-1/

there used to be videos of the Lightning demonstrations @ http://www.electricstuff.co.uk/

[haklesup]

Wow!!!

Glad to hear you weren't killed. The hearing should come back (but your doctor will know better than I). Did insurance cover it or was it below the deductable?

It's clear where the lightning came out but do you have any idea where it went in (actual sky strike point). Sounds like it might have hit the cable or phone line on the utility pole but it would have been right at your nearest pole else those wires would have fused before entering the house. I suppose if no neighbors were zapped, it's likely the strike was directly onto your house somewhere.

A pointy rod at the ends of the roof peak and #6 or larger wire to a good earth ground rod the proper distance from the house is probably the best medicine. Personally I would consult 1 or 2 properly licensed contractors and then decice if it's a DIY or pay as you go job.

If it did hit the flag pole or metal shed too, you may never know, both are conductive enough it may have left no evidence.

Lightning does frequently strike the same place twice or more. Consider it a wake up call not to ignore.

[dacflyer]

there are sites for lightning rod tutorials...
and theres places that will sell you the parts also.. part by part or kits..
i repaired mine cheap.. and actually the parts are very fair priced also.

hager lightning protection - http://www.harger.com/
lightning rod parts - http://www.lightningrodparts.com/index.html
modern lightning protection co. - http://www.modernlightning.com/

internets full of sites..google " lightning protection " or "lightning rods"

good luck.. its easy to do...

[mthornton]

I'm an electrician at a ski-area in eastern BC, where we get lots & lots of heavy lightning each summer. The lifts themselves include significant amounts of electronics, including on the towers themselves. All of our lifts have experinced direct hits many times, yet with relatively minimal damage to the digital control systems, the SCR drives & safety systems. The wire-ropes themselves, as well as the overhead safety system wiring, are often over 1000m in length. You would think things are the best damn lightning rods immaginable.
The grounding methods are such that the potentials of the steel-work are kept as close as possible to the natural ground potential in the immediate vicinity. This applies to each tower as well as each station. The stations have surrounding ground-grids (at least on the newer lifts), all metal roof clatting is all bonded to ground, along with the station steel. All bonding ties into to the electrical system grounds. There is no attempt to use grounding cables heavy enough to carry all the current generated during a hit. The ground bonds simple keep everything at the same potential as the surrounding earth.

Lightning seems more attracted to objects which can build up significant charge WRT earth, like an unbonded metal roof. Sounds like you have done all that, and thus should have minimum worry.

Electrical code required your panels must be grounded to provide a return path for fault-current during an electrical fault, to provide the best chance for the protection to blow. Nothing to do with lightning at all.
M

[dacflyer]

hi, thanks for the info,
yah, i belive i have done all thats possible also to keep everything safe as well.
i am sure that if i do get a direct strike stuff might become toast, but there should be minimal structure damage, if nay at all.
next week the power company should be connecting me to the grid..
right now the county inspector is butting heads with the power company..
the county inspector has little knowledge on solar right now, and i am the 1st in my own to have it, so its a learning curve for all here.. i have clued them in on a lot of stuff.
one complaint the inspector has is that he says THE BOOK (N.E.C.) sez... you cannot have 2 meter bases on a single structure without a firewall.. ya well thats does not pertain to solar use. that is being an acception, which he did not know yet. but its common all across the USA right now. and that one reason why he did not want to pass inspection of my system yet.. but strangely wednesday i found a PASS sticker in my mailbox that day ( big dog in my yard )
so i called the power company, and they will be calling me next week to set up a tie in day..

[dyarker]

????? This is a question ??????

I don't understand why two meters. From reading at other sites (not authoritive) I was led to think that single meter ran backward if your solar system generated more power than you were using and fed the extra into the grid (selling power to power company).

???? Repeat, that was a question; and I'm curious. ????

Cheers,