How concerned are you about lightning?

Cariboocoot

Re: How concerned are you about lightning?

The debate about lightning protection has been going on ever since Ben Franklin flew his kite.
It is impossible to have an absolute answer because there are too many variables involved.

When Thomas Edison was asked if would be a good idea to put lightning rods on a church he responded: "Certainly; Providence is often forgetful."

You can take reasonable measures to reduce risks, but you can never eliminate them all. It is unfortunate that some of the 'rules' actually increase risks. All I can suggest is: spend some of the money on insurance.

northerner

Re: How concerned are you about lightning?

Cariboocoot wrote: »

You can take reasonable measures to reduce risks, but you can never eliminate them all. It is unfortunate that some of the 'rules' actually increase risks. All I can suggest is: spend some of the money on insurance.

That's true, but I would think that some if not many people who put in off grid systems on their own accord (ie without a permit) won't be covered by insurance.:roll:

It appears that the majority of lightning induced damage are on systems that are not properly grounded. I think one can do plenty to mitigate the risk, but as coot says not eliminate them altogether. We are at the mercy of the weather gods!

BB.

Re: How concerned are you about lightning?

NorthGuy wrote: »

If I have a solar array that is 300 ft away, how do I make it equipotential? Or if you have several buildings hundereds feet away connected to the same electric system, how do you make them equipotential?

That is the problem... You cannot short of placing a 1/2 thick 40 arc copper plate down on your property and building on top of it.

Especially with RF energy, you have to assume that there will be an electro magnetic field that changes over time and distance.

The best way to address the problem it to create a Faraday Shield around your home, and around the out buildings. Any electrical connections that "penetrate" the shield should go through lightning arrestors.

And do not connect AC/DC distribution grounds in more than one place to the neutral/return buses (i.e., one AC ground in main panel, one DC Ground from battery bank return to AC+DC master ground rod).

If you require local isolation, then you would use an isolation transformer which would let you have a local ground referenced neutral (say in a pump building, out building for manufacturing, etc.). That helps provide up to around 2kV of isolation (the rating of the transform input to output isolation). But, where direct strikes are involved--10 miles of arc is not going to stopped by 2kV of insulation.

If you have multiple ground connected to your (for example) AC Neutral... All you have done is forced current to enter the AC Neutral from the two widely displaced ground rods--They are taking the voltage gradient in the soil and "shorting it out" with the AC wiring.

That is why it is suggested to have a master ground rod where all electrical ground terminate, and if more grounding is need (such as poor soil conditions) that you arrange additional ground rods in a circle around the master rod and run a ground wire from the master to each additional rod. This keeps any "circulating" currents from being injected into your power lines.

The "equal potential" wiring you see in the diagrams does two things. One is provides the DC/50-60 Hz grounding required to trip a circuit breaker if there is a short in the local power grid. And second, if the buried cable is exposed to surrounding soil, the first ten's of feet or so will help dissipate the energy into the soil. But it does not magically make everything at "zero volts" everywhere over hundreds of feet of distances.

So, you are usually back at looking at what can happen and what are you trying to protect against.

Building a Faraday Cage is "simple". That keeps all electrical energy outside the house and keeps people inside safe. Anything that goes into the "cage" should have some sort of electrical arrestor to discharge excessive voltages/energy to the ground/outside of the cage before it enters.

When you have an out building with AC power (for example)--You look at what is happening. A nearby strike creates a electric field/gradient across distances. The best you can do is short it locally at the source (say home AC panel/ground) and at the destination (surge suppressor between AC and Ground). That helps keep people (and hopefully hardware) safe in both locations. But--You can still end up with some damage (pierced insulation between locations, destroyed lightning/surge suppressors/etc.)--But that is hopefully the limits of such damage.

More or less, the AC equipment should be OK up to ~1,800 VAC (internal insulation design limit/tested act factories under UL/NRTL manufacturing tests). And over that, hopefully your surge suppression and directing lightning energy away from vulnerable points of entry will take care of voltage in excess of those limits.

I had posted here in the past a radio transmitter that was always being taken off the air (commercial or NPR type station) from lighting strikes. After a firm went through and grounded the heck out of everything/surge suppression/etc.--they never had any more problems (unfortunately, there was not much detail about the work done). So it can be done.

But I have also read about enough stories of Fire Observation/Watch Towers (built on top of mountains in forested areas) where they seemed to have lots of heavy lightning cables, rods, etc... And yet there were reports of static discharges of several feet inside the towers when thunder storms where in the area (and needing to sit on wooden stools, use wood poles to flip switches, etc. to avoid shocks)--I don't assume that the forest service was "dumb" and did not do everything possible to protect against high electric fields and lightning strikes--But I have always wondered what was not "right" about those installations--Or are these issues that are unresolvable? (I don't think so).

-Bill

BB.

Re: How concerned are you about lightning?

northerner wrote: »

I also plan to do a temporary total disconnect from the solar array (power, and ground lines) in the event of a storm. This could be handled automatically by detecting an electric field, and then activating relays to do the disconnect.

A standard relay is not really going to do much where lightning is involved.

I think I have seen a recommendation that if this is your solution (i.e., disconnecting power sources during a thunder storm), then it should be a plug+cable and there should be ~8-10+ feet or more separation between the plug/cord and the building/vessel/vehicle. And just level the cable on the ground (or in a grounded enclosure) so that if it does become energized, the shortest/best path is not to your home/etc.

Of course--There is always the problem that when you notice lighting in your area--It grabbing a outdoor plug/cord set connected to a large solar array (or wind turbine on a tower) the best place for you to be...

I have linked to lighting alarms before (measure earth's electric field strength) to provide early warning--But I have not heard of anyone trying that here.

Lightning Prediction Systems

For a park in a location with lots of electrical activity--Probably not a bad idea.

-Bill

northerner

Re: How concerned are you about lightning?

If you have multiple ground connected to your (for example) AC Neutral... All you have done is forced current to enter the AC Neutral from the two widely displaced ground rods--They are taking the voltage gradient in the soil and "shorting it out" with the AC wiring.

That is why it is suggested to have a master ground rod where all electrical ground terminate, and if more grounding is need (such as poor soil conditions) that you arrange additional ground rods in a circle around the master rod and run a ground wire from the master to each additional rod. This keeps any "circulating" currents from being injected into your power lines.

So are you saying it's not recommended to put 2 or more ground rods in, in a straight line? I always understood that the better the connection to ground, and the more ground rods, the better.

northerner

Re: How concerned are you about lightning?

BB. wrote: »

A standard relay is not really going to do much where lightning is involved.

-Bill

But I would also have a surge arrestor on the inside that should handle most anything, other than a direct strike. I would think disconnecting with a relay is better than a direct connection. I don't think you can do anything in the event of a direct strike.

BB.

Re: How concerned are you about lightning?

northerner wrote: »

So are you saying it's not recommended to put 2 or more ground rods in, in a straight line? I always understood that the better the connection to ground, and the more ground rods, the better.

The difference is ground rods (typically) have their own physical wiring. You would not (for example) run the AC neutral out the building into a trench with a ground rod, then run 200' to an out building and then attach another ground rod to the neutral, finally entering the out building.

That could inject lighting current into the AC neutral, plus magnetically couple and induce currents and possible over voltage spikes into the parallel wiring runs.

[FONT=Fixedsys]Not recommended:

================================ AC run
   | two neutral bonds        |
 _______                  _______
 / / / /                  / / / /


How I would suggest multiple ground rods:

================================ AC run
   | one neutral bond/two ground rods
   |-------------| 
_______        _______
/ / / /        / / / /

[/FONT]

-Bill

northerner

Re: How concerned are you about lightning?

BB. wrote: »

The difference is ground rods (typically) have their own physical wiring. You would not (for example) run the AC neutral out the building into a trench with a ground rod, then run 200' to an out building and then attach another ground rod to the neutral, finally entering the out building.

That could inject lighting current into the AC neutral, plus magnetically couple and induce currents and possible over voltage spikes into the parallel wiring runs.

-Bill

Ok, I see what you're saying Bill.

It appears that achieving the equalization of potential around your home may be worth while installing. Essentially can be done by trenching in a ground wire around your home, and placing ground rods on the corners as you recommended Bill. Here are a few more tid bits about grounding for lightning.

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

BB.

Re: How concerned are you about lightning?

Multiple ground rods to a ground cable system yes.

A ground rod at the main panel, another isolated ground rod to the battery negative post/bus, another from cable/phone ground to the cold water pipe, etc. are all perfectly good grounds.

HOWEVER, the problem is each ground is "local" to where the earth contact is made. So, if you are making a (wired) phone call while typing on your computer (and/or using a hardwired to computer modem/cable modem/Ethernet cable, etc.-- In such an above system, each would have a "different" zero volt source/ground reference. A near by strike (say near the AC main panel) will have higher relative voltage (of hundreds to thousands of volts) to that of the cold water pipe that enters the home from the other side where the phone/cables lines were ground/surge referenced--And the difference is brought there right to your desktop/lap.

Even using 6 awg of "equal potential" cabling connecting the two together still has the "impedance issue" that allow RF voltages to be vastly different between the two ends of wires 10's of feet apart.

The idea of bringing everything at one location of the home (water, gas, electricity, cable, phone, etc.) means that they all now have the "same" electrical potential as every other device/large chunk (tubs, sinks, large appliances) of metal in the home. So, there is less chance of having dangerous voltage potentials between various items and people in the home/building.

-Bill

northerner

Re: How concerned are you about lightning?

Yes, I was aware of that Bill and thanks for making the clarification to others as well!

Vic

Re: How concerned are you about lightning?

EDIT: This post disappeared, but thanks to AutoSave it is restored... Thanks N AZ W&S!

There seems to be nothing absolute, regarding lightning. We all do our best to do our best. What may help protect from distant strikes might increase the odds of a direct hit.

The Broadcast industry erects towers that often take thousands of direct hits per year in some locations, and generally, experience no damage. These towers usually use copper strap to connect towers to the ground systems.

For our systems, run perimiter UFER-type grounds around structures, and trench grounds between buildings, and coax feed lines in ground trenches. The latest project uses a 270 foot

But all bets are off when lightning hits.

One PV roof array is grounded with separate run from the roof to trench ground, and on to the main service entrance ground. The other roof array is presently ungrounded.

It is very difficult to make a direct connection from roof PV frames to a grtound system. Any turns increase the Z of the ground. And some consider a ground dropping from the edge of the roof to the ground unsightly.

As always, too many trade-offs, and differing opinions. My opinions, Vic

westom

Re: How concerned are you about lightning?

This and next posts addresses many from the past 18 hours. And unfortunately repeats what was answered in previous posts (ie 300 foot distant array question) and not understood.

First, NEC is only what is minimal for human safety. It says nothing about transistor safety. We are discussing the earth ground system that must do both human safety and transistor safety. NEC says nothing about transistor safety. The National Fire Protection Association ignores transistor safety. NFPA is only about human safety.


Second, a rod must be at least five feet into conductive soil. If the frost line is 6 feet, then the rod must be 11 feet. To get into soil that is more conductive because it did not freeze last winter and is not frozen next winter. In most locations, an eight foot ground rod means only its lower six feet does most earthing.

Ten ground rods separated two meters apart and at least five feet below the frost line are one single point ground. Better (for equipotential) is to locate rods about the house (as the professional's app note demonstrates). Not in a line away from the house.

Surges are not just from lightning. Another reason why disconnecting is unreliable. This surge type can exist when a car slides on ice into a utility pole. A protector must be sized sufficient (ie 50,000 amps) to earth all types of destructive surges. A direct lightning strike being one type that never causes damage (even to any protector) when incoming utility wires (or solar panel wires) are properly earthed by that protector.


Third, insulation for protection is impossible. How does that insulated panel, or millimeters in an open switch, isolation transformer, or relay stop a surge that crosses three kilometers of sky? As posted earlier. A surge is not a voltage source. It is a current. Voltage increases as necessary so that current will flow uninterrupted. Voltage increases to blow through 1800 volt solar panel isolation. Because nothing stops that current. Because voltage increases as necessary to pass (blow) through any (rumored) insulator.


Fourth, arrays mounted on wood are electrically connected to earth. Wood is an electrical conductor for the same reason lightning strikes wooden church steeples. That isolation only works if lightning is given a many times more conductive path to earth - ie copper wire. And that was introduced in elementary school science - the Ben Franklin lightning rod.

Nothing as in 'nothing' will stop, block, or filter a typically destructive surge. Any claim about insulation or isolating is ignoring what Franklin demonstrates in 1752. Current 'always' must be given a path to earth that is not destructive. Otherwise damage results by increasing voltage and blowing through the insulator. Again, nothing as in 'nothing' stops a surge.

Previously posted was another suggestion. An earthed catenary above solar panels means the best connection to earth is via catenary; not via a solar panel and its wooden mounts. Protection is always about what Franklin demonstrated in 1752. As originally taught in elementary school science.

westom

Re: How concerned are you about lightning?

Fifth, if solar panels are 100 meters away, then do what that professional's application note demonstrated. He showed an antenna tower. Replace that tower with solar arrays. Again, you have two (or three) separate structures. Do what all telcos do everywhere in the world. A single point ground exists at each structure. A wire between any structure must connect to each structure's single point ground before entering.

Do exactly same for each group of solar arrays. Each group is just another building. Each must have a single point ground. Even better, surrounded by a ground loop. Then a wire from panel to house must be grounded to that loop - the earthing electrode.

Again, the application note was labeled "Need for Coordinated Protection":
http://www.erico.com/public/library/fep/technotes/tncr002.pdf

In essence, each structure has its own Faraday cage (as discussed by BB). Cage is improved if lightning gets to earth via a catenary.

See (in that app note) a ground wire interconnecting both single point grounds? That makes both single point grounds more conductive. And addresses other problems not discussed - to keep it simple.


Sixth, a direct lightning strike within 10 meters of a long wire antenna induces thousands of volts on that antenna. The effect created by electro-magnetic fields. Connect the antenna lead to earth via an NE-2 glow lamp. The same tiny neon bulb found inside night light wall switches. That bulb may conduct a few milliamps. Therefore thousands of volts on the antenna are now reduced to ten.

Transients created by fields are that tiny. Are made irrelevant by solutions that trivial. Many see the thousands volts. And never learn that voltage virtually disappears when milliamps connect to earth. Again, it is not about voltage. Surges are a discussion 'always' about current. Voltage only exists when someone foolishly tries to stop, block, or filter a surge (ie using wood). Nearby strikes are trivial. If a properly installed solution makes direct strikes irrelevant, then nearby strikes are not even discussed.


Seventh, an example applies here. Lightning seeks a best connection to earth. So it strikes a tree. Some ten meters away is a cow. Cow dies due to a direct strike. The uninformed 'assume' a cow was struck by a lightning bolt rather than learn why that cow died.

Once that current is in earth, then it travels kilometers to distant charges. What is a best path? Up a cow's hind legs and down its fore legs. The cow was also in the current path. Because the cow had multipoint grounding.

How to protect that cow? The professional's application note and previous discussions make an answer obvious. Either a cow must stand with all four legs together - a single point ground. Or the cow must be surrounded by a buried wire - a ground loop.

Lightning in the sky did not directly strike the cow. And lightning E-M fields were not harmful. But many make such assumptions. Lightning struck that cow directly from earth. Because the cow did not have a single point earth ground.

westom

Re: How concerned are you about lightning?

Eighth, there was no debate. Too many only know from hearsay and myths sold on retail store shelves. Concepts demonstrated by Franklin are found in every facility that cannot have damage. For example, a telco switching center (CO) will suffer about '100' surges with each thunderstorm. How often is your town without phone service for four days after each storm? Never. Because these principles (all based in earthing) are that well proven, that routine, and still that little known by the public.

A concept that seems to be almost impossible for some to understand. Voltage is irrelevant. Protection is about the current. Does a lightning rod do protection? Of course not. That rod is only as effective as its earth ground. Too many see the rod. Then foolishly argue about pointed verses blunt. While completely ignoring what eyes ignore - the earthing electrode.

BTW, despite so many myths that promote pointed as superior ... a blunt rod provides better protection. Learn from the science that advocates blunt rods. Ignore popular hearsay that still promotes myths and pointed rods.


Ninth, despite previous posts that said this - protection is never about grounding equipment. Protection is always about earthing the surge. And locating equipment farther from that ground and protector.


Tenth, as BB and others noted, a connection to earth must be short. Multiple grounds (as demonstrates by the cow) are also harmful. Surges are RF energy. That means every foot shorter the connection from a wire to earth ground increases protection. Every one foot. Because protection is defined by how short a connection to earth. Protection increases when electronics are farther from that protector and earthing.


Eleventh, water pipes are no longer considered sufficient grounds. We are discussing transistor safety. But even the National Electrical Code (only for human safety) says the water pipe ground is the only ground that is insufficient. And is even worse for earthing surges due to things that increase impedance such as solder joints, 90 degree turns, etc.

As lightningsafety.com notes, the water pipes must be integrated into the earth ground system. Because every conductor (including copper pipe) must connect to the single point ground. Or become the incoming path of a surge (just like the hind legs of that cow).

Just remember, water pipes are inferior grounds for surge protection. Better grounds such as a plate, rods, etc must also exist because water pipes are not even sufficient for human safety and the NEC.


And twelve. Protection from direct lightning strikes is so routine that damage is considers a human mistake. Protectors are dumb science. Protectors without the short connection to earth can even make appliance damage easier. Also simple science. But the art is always about earthing. For example, if the ground froze last winter, then it is less conductive this summer.

Where does the investigation start when a direct lightning strike causes damage? The earthing system and connections to it. Another citation - professionals went to a radio station to fix defective grounds installed / modified by engineers who still did not learn this stuff:
http://www.copper.org/applications/electrical/pq/casestudy/nebraska.html

Many will read that case study and still not grasp critically important points. For example, protection is about layers. No protector ever defines a layer. Each layer of protection is the earth ground.

We discussed secondary protection - the structure's single point earth ground and 'whole house' protector. They also upgraded the primary protection layer in that case study. A picture demonstrates what to inspect in the primary protection layer:
http://www.tvtower.com/fpl.html


Finally, many paragraphs are repeating what was already posted. The previous posts were long. Therefore little will be understood in the first read. This post is also long. Chock full of important details (such as water pipe is an insufficient ground). Reread it multiple times and still see new concepts.

In every case, protection is only about how that current gets to earth. Not voltage. Current. Even that was repeated multiple times and often not grasped.

So yes, I expect plenty of questions. Because what was well understood even 100 years ago is still completely new to so many. Because many popular myths may need be unlearned to understand basic concepts. For example, wood is an electrical conductor. Even that concept is difficult for some.

Cariboocoot

Re: How concerned are you about lightning?

This is why cows lie down before a storm.

niel

Re: How concerned are you about lightning?

great discussion guys. the questions on grounding are important in trying to relieve a surge and my hats off to all of you in pretty much getting it right on the money and weston you are really hitting good points especially with this basic diagram. http://www.erico.com/public/library/fep/technotes/tncr002.pdf

i should point out that the bare copper wire interconnections for the rods should be underground and the use of at least #6 due to soil acting upon the outer copper of the interconnecting wire. burying the wire should be done to at least a depth that no harm from most other possibilities should occur such as gardening. I often say at least 1ft down. this wire does not have to be below the frost line as the rods shall meet that requirement.

this does not stop a surge altogether as was pointed out that much of the energy is in the radio spectrum and this will pass right through to the equipment and wiring, unless of course it is buried far below ground and is difficult for the rf to reach it then. if one uses lightning rods and the wire drapes down to the ground in different directions that a sort of blanket effect occurs for much of the rf energy. this is a faraday cage and unless it is solid metal all around then one can't guarantee there won't be a surge to reach the interior of the cage, but it could be dispersed or attenuated some by the cage. the pvs can be within the cage area and not be shaded so the interior of the cage does not necessarilly mean the interior of the house or structure. even in proximity to the cage can shade the wires and equipment electrically, being carefull not to shade pvs from the sun also, if below the top of the rod and close enough to it.

also, surges usually do not go backwards as the grounded surge is very unlikely to go back up another common ground lead if done properly. the pvs mounted on wood are somewhat insulated, but if the wood gets wet all bets are off. even dry there's no guarantee it won't travel down it as it may still be more conductive than the surrounding air. trees may also divert lightning being higher up, but it is also longer with more resistance to ground. even if the pvs were magically suspended in the air the lightning could still be attracted to it because of its lower resistance than the surrounding air being made of highly conductive metals.

as to a pv array 300ft away keep in mind the ground resistance in that 300ft is quite high from one end to the other. your concerns of voltage differentials is quite real though. when the distances become closer in then i would recommend an underground cooper tie wire and bare #6 at a minimum. most utilities have poles with grounds on each of them, but they are spaced farther apart and not tied underground. 2 reasons for this are 1> the ground resistance is higher which would knock down big potentials of voltage to develop and 2> even if they did the utility is too cheap to put extra copper underground to tie all of those poles together making for a bit of a risk for some voltages differentials to develop. that risk would be increased if the soil conductivity is bad.

it is a very complex subject matter and it is not a matter of being able to memorize nec rules, but more to envision what high voltage and its related surges are likely to do. most of us, even learned, have difficulty accounting for every possibility. it's unpredictability does make it an uncertain science to be 100% sure of protectiveness and stuff happens sometimes that aren't accounted for in foresight, but it does have a great deal of real solid science behind allot of the efforts so it is not without some success.

westom

Re: How concerned are you about lightning?

niel wrote: »

i should point out that the bare copper wire interconnections for the rods should be underground and the use of at least #6 due to soil acting upon the outer copper of the interconnecting wire. burying the wire should be done to at least a depth that no harm from most other possibilities should occur such as gardening. I often say at least 1ft down. this wire does not have to be below the frost line as the rods shall meet that requirement.
this does not stop a surge altogether as was pointed out that much of the energy is in the radio spectrum and this will pass right through your walls to the equipment and wiring, unless of course it is buried far below ground and is difficult for the rf to reach it then. ...

Matters little if wires are overhead or underground. The "Need for Coordinated Protection" demonstrates same. Even underground phone wires must be grounded like overhead wires. For many reasons including and not limited to why a cow was killed.

Safety code says how deep a wire must be buried. Numbers such as #2 AEG and at least 18 inches deep are typical.

As others noted, a flat copper wire is best for low impedance. But also earth so that the conductor remains intact for many generations. Braided or flat wires corrode and fail too quickly under ground. Wires must also address harsh environmental conditions.

Some may protect a connecting wire inside metallic conduit. Now that wire is, essentially, not conductive. Again, earthing and how to connect to it is more an art.

Another example: suppose two separate buildings are interconnected by network cables. If single point grounding is not implemented, then a lightning strike to one building is as if a lightning rod was connected to electronics inside the other building.

Protection is always about how that current gets to earth. Makes little difference if wires are overhead or underground. Same protection techniques are still required.


All appliances already contain superior protection. Cited was an antenna designed to maximize power from fields generated by nearby strikes or radio station. What makes fields from nearby lightning irrelevant? One tiny neon glow lamp. Appliances already contain protection that also makes field generated transients irrelevant. Appliances already contain significant protection.

Your concern is a rare transient (typically once every seven years) that can overwhelm protection already in a properly designed panel or power converter. That rare and destructive transient current made irrelevant when properly earthed - either directly (ie catenary) or via a protector.

NorthGuy

Re: How concerned are you about lightning?

westom wrote: »

So yes, I expect plenty of questions. Because what was well understood even 100 years ago is still completely new to so many. Because many popular myths may need be unlearned to understand basic concepts. For example, wood is an electrical conductor. Even that concept is difficult for some.

Thank you westom for your fascinating description.

Probably there's no good solution for panels located at a distance. Two grounded Faraday cages 300ft apart with wires between them looks a lot like a cow standing on two legs. And the better her legs are grounded, the more is the chance for her to die. The cow would be better off standing on one leg, with her other legs ungrounded, wouldn't she?

Protective grounded wire above panels looks like a good idea, sort of a lightning rod. Would I live panels ungrounded then because they're sort of inside the cage?

westom

Re: How concerned are you about lightning?

NorthGuy wrote: »

Probably there's no good solution for panels located at a distance. Two grounded Faraday cages 300ft apart with wires between them looks a lot like a cow standing on two legs.

Two separately located panels are similar to those two separate buildings. If wires that interconnect two separated panels are not earthed to each panel's single point ground, then you have the previously posted example. Lightning striking one building (or panel) is simply a lightning rod connected to electronics inside the other building (or second panel).

You have a building and two separated panels. So you have three separate buildings (similar to three separate cows). Each 'building' must have its own single point earth ground. Any conductor that enters or leaves each building must have a short (withing feet) connection to that single point earth ground. If any one wire interconnects two panels, then that wire must connect short to each single point ground before connecting to that panel or controller.

Does not matter if any interconnecting wire is overhead or underground. Same rules apply.

BTW, it also applies to golfers. In one situation, golfers took refuge inside a small shelter. When lightning struck earth, some were shocked. Because the shelter was not surrounded by a buried ground wire.

However, take a lesson from Caddy Shack. If having a best game, stay out of that shelter and keep playing. God will be with you.

NorthGuy

Re: How concerned are you about lightning?

westom wrote: »

Any conductor that enters or leaves each building must have a short (withing feet) connection to that single point earth ground.

I cannot understand this The wires between panels and the house are current carrying wires. You cannot connect them to the ground. You can connect the negative wire, but then you cannot connect the positive wire, because if you do you effectively short them.

Cariboocoot

Re: How concerned are you about lightning?

NorthGuy wrote: »

I cannot understand this The wires between panels and the house are current carrying wires. You cannot connect them to the ground. You can connect the negative wire, but then you cannot connect the positive wire, because if you do you effectively short them.

The nature of a lightning arresting device is that it creates a conductive path for the high frequency, high Voltage energy but does not make a dead short that would kill the operating power.

Used to have gas discharge tubes for this, but I think they fell out of favour back in the age of the dinosaurs.

westom

Re: How concerned are you about lightning?

NorthGuy wrote: »

I cannot understand this The wires between panels and the house are current carrying wires.

This expression was repeated often. A wire is grounded (either directly or via a protector).

Let's review some other incoming utility wires. Best surge protection on cable is only a typically green wire from its shield to single point earth ground. No protector required. That wire makes the connection and best protection.

Telephone cannot have a direct connection. So all telephones are connected to the same earth ground via a protector located inside an NID (where their phone wires meet yours). To a surge, that wire connects directly to earth as if the protector was not there. To telephone signals on the same wire, no connection to earth exists.

When discussing protection, we say every wire must be earthed (as seen by a surge). And so often repeated was this expression: either directly or via a protector.

Pre 1900 protectors did this with spark gaps. Later technology was an earth connection via a gas discharge tube (GDT). Phone companies later used something called carbons. Today, that connection to earth is typically via semiconductors (Transorbs, avalache diodes, thyristors, etc) or via varistors (MOVs). These devices have capacitance. So radio operators still use GDTs - a lower capacitance protector.

You are conducting DC currents. So capacitance is irrelevant. Most any device would be sufficient to connect each wire inside that cable to earth. MOVs are a typical choice. Best solution per dollar. However you chose the protector. Its manufacturer chooses which technology.

A connection from every wire to earth is either directly (a hardwire) or via a protector. How it was done even in the 1800s.

NorthGuy

Re: How concerned are you about lightning?

The surge protector that I recently bought in Home Depot and installed into the AC distribution panel had to be installed between hot wires and neutral, not ground. Looks like they tried yo avoid connection to the ground for some reason. Why could that be?

westom,

So, with AC wires spreading through several buildings, each having its own ground, do you think it's a good practice to bond neutral to the local ground directly in each building? And install protective devices between hot wires and ground?

Cariboocoot

Re: How concerned are you about lightning?

NorthGuy wrote: »

The surge protector that I recently bought in Home Depot and installed into the AC distribution panel had to be installed between hot wires and neutral, not ground. Looks like they tried yo avoid connection to the ground for some reason. Why could that be?

I suspect they are counting on the neutral being bonded to ground at that point, which it should be. As such it would actually provide a path from each hot leg to ground for the hi-energy to travel.

westom

Re: How concerned are you about lightning?

NorthGuy wrote: »

So, with AC wires spreading through several buildings, each having its own ground, do you think it's a good practice to bond neutral to the local ground directly in each building? And install protective devices between hot wires and ground?

First, be very careful which 'ground' is discussed. Safety ground is electrically different from earth ground.

A main breaker box must have a common bus that connects the utility's incoming neutral, all household neutrals, all safety grounds from receptacles, and the earth ground. Those connections to a common bus required for human safety. We use (and upgrade) the same system to also earth a surge.

From the main box must be a wire to an earthing electrode (rod, plate, Ufer ground, buried wire). Typically a bare copper quarter inch wire. How long is it? For example, if it goes up over the foundation and down to earth, then it is sufficient for code. And compromises surge protection. Too long. Sharp bends going over the foundation. Not separated from other non-grounding wires. A best connection is through a foundation and down to earth. Shorter. No sharp bends. Etc.

Older homes do not have this now 'always required' earth ground. If not, it should be installed 1) to increases human safety, and 2) to have the single point earth ground so essential to surge protection.

Implied is that other buildings have sub panels where a safety ground and earth ground are separate. If so, another type of 'whole house' protector might be necessary. However, if other buildings also have a main breaker panel (as described above), then those panels also get a 'whole house' protector.

The term separate buildings can be ambiguous. Because numbers are not provided. As a general rule, a building withing 20 feet of the main building is considered all one building (electrically). A ballpark rule. But again, that is where earthing becomes an art. And maybe another example of how to learn from future damage.

vtmaps

Re: How concerned are you about lightning?

westom wrote: »

Another solution is to suspend a catenary above the panels. The a best path to earth is through that catenary to earth.

Is this practical? I don't think I've ever seen a catenary ground path. It would have to be rigid or it would not remain a catenary in the wind.

--vtMaps

northerner

Re: How concerned are you about lightning?

Would you recommend installing a lightning rod on the roof of my home? The roof is metal and the panels are mounted on the roof. The highest object on my roof currently is a metal chimney. I was thinking of putting in a rod, and running a braided wire straight down to my ground to divert any potential surges away from the panels and chimney.

Also, I was thinking of installing a surge capacitor on the inverter output. Does anyone use this for protection? I know that the Midnite surge suppressors are faster acting and may take care of those sharp spikes?

BB.

Re: How concerned are you about lightning?

The short answer is a metal building is still easily damaged by lightning. The metal is not heavy enough (or low enough resistance) and will still generate enough heat to blow holes in the sheet metal.

Also, the metal to metal bonds in roofing are "incidental type"--Meaning that as the lightning spreads out, each connection can be a point where the lightning current can generate heat/voltage differences (shock/lightning finds a different path, etc.).

Ideally, you would run a lightning control system on a metal (or metal roofed) building just like you would on any other building. And on that metal chimney too. (in my non-expert humble opinion/understanding of the issues).

Regarding adding surge suppressors to the output of the AC Inverter--A very good idea. Windsun (our admin from NAWS) a few years ago said that the majority of lightning induced off grid AC Inverter failures was on the output stage (not the DC input stage)--So I would think that suppression on the output of the AC Inverter should be a big help.

-Bill

northerner

Re: How concerned are you about lightning?

BB. wrote: »

The short answer is a metal building is still easily damaged by lightning. The metal is not heavy enough (or low enough resistance) and will still generate enough heat to blow holes in the sheet metal.

Also, the metal to metal bonds in roofing are "incidental type"--Meaning that as the lightning spreads out, each connection can be a point where the lightning current can generate heat/voltage differences (shock/lightning finds a different path, etc.).

Ideally, you would run a lightning control system on a metal (or metal roofed) building just like you would on any other building. And on that metal chimney too. (in my non-expert humble opinion/understanding of the issues).

Regarding adding surge suppressors to the output of the AC Inverter--A very good idea. Windsun (our admin from NAWS) a few years ago said that the majority of lightning induced off grid AC Inverter failures was on the output stage (not the DC input stage)--So I would think that suppression on the output of the AC Inverter should be a big help.

-Bill

So would a lightning rod be a good idea then? My other question related to using a surge capacitor in addition to a Midnite SPD, thanks.

Cariboocoot

Re: How concerned are you about lightning?

I know I'm going to regret asking this but ...
What is a "surge capacitor"?

The MidNite SPD should take care of any transient Voltage spikes that could reasonably be expected. Anything they can't handle, probably nothing else would.

As for lightning rods, how likely are strikes there? Survey other buildings in the area and see if they have rods. That's usually a good indication of the need and propriety.