help with lightning protection

solarsquirral

hi guys

looking for some advice in the lightning protection area
currently my system has two ground rods
one at the ac panel and the other at the inverter about 50 feet away
the generator also has a bare 6 ga running to the same rod as the generator

ive heard there might be issues with multiple ground rods on same system
im also wondering which lightning arrestors would work well and where i should place them

im thinking between the array and controller

also the ac side and inverter

any where else

delta or midnite???

where sould i ground the array to??

ive been shutting it down during lightning but would like to have a bit more protection

BB.

Here is some reading to start (from the FAQ Thread):

BB. wrote: »

Re: Working Thread for Solar Beginner Post/FAQ

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 FAQ:

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

BB.

I should add Midnite for the surge protectors. Modern design for the Midnite.

The Delta is an old design (at least the typical Delta--The little I know) is a pair of simple contacts in a sand filled container (arc gap).

You can read/watch their product testing:

http://www.midnitesolar.com/products.php?productCat_ID=23&productCat_ID=23&productCatName=SPD

-Bill

mike95490

3 things going on.1) AC electrical safety ground (the 3rd wire, ground rod) This is what the building inspector is looking for.

2) Lightning near strike. Can induce high voltages in the wires, Midnight and Delta protectors can help save your gear. I use both.

3) Direct hit by lightning on any of your gear/wiring. It's all going to be dead and/or vaporized. Lightning rods, towers, protection (high) wires will help, but they may cost as much as the gear you are trying to protect.

Dave Angelini

mike95490 wrote: »

3 things going on.1) AC electrical safety ground (the 3rd wire, ground rod) This is what the building inspector is looking for.

2) Lightning near strike. Can induce high voltages in the wires, Midnight and Delta protectors can help save your gear. I use both.

3) Direct hit by lightning on any of your gear/wiring. It's all going to be dead and/or vaporized. Lightning rods, towers, protection (high) wires will help, but they may cost as much as the gear you are trying to protect.

Also keep in mind that if you have spares because of number 3, they must be protected in a grounded metal cage. Do the best you can and a prayer now and then can't hurt.

jonr

My view is:

1) provide a preferred path for lightning
2) avoid multiple ground points
3) use surge suppressors (probably multiple MOVs) between all wires (hot, neutral, ground, phases)

Mountain Don

jonr wrote: »

2) avoid multiple ground points

I believe that needs some clarification. I thought multiple grounds rods were good as long as there was one continuous wire connecting them to one (and only one) common grounding point in the electrical system? More than one ground rod may be required to get to or below the 25 ohm NEC rule. And then any lightning protection system using air terminals and heavy cabling should have more than one grounding rod or plate and those grounding rods should be separate from the power system grounding and should have even less resistance for best results.

jonr

Agreed. Consider multiple rods or plates in the same area a single ground point. And completely isolated grounds without power wires running next to them are OK.

The idea that grounding something will attract lighting would have merit - except that after traveling a mile or more through air, another 20' or so makes no significant difference in the probability. Ie, it will still strike and happily travel through your slightly less conductive (on a percentage basis) building to get to ground.

Graham Parkinson

Hmmm.

The point about multiple grounds and a nearby strike is that the huge earth currents result in large voltage gradients in the earth.

These are shorted out by the expensive wiring between the multiple ground points.

Think of the earth voltages per meter produced by a typical lightning strike of say a million amperes hitting typical soil resistances of say 100 Ohm-m ( face resistance of a 1 m cube of soil). Ignoring geometrical effects this suggests on the order of 10,000 volts per metre!

An interesting effect seen in airborne magnetics geophysical data is that hilltops often get magnetized by the large ground currents that result from repeated lightning strikes.