Panel Earthing

[Jaco De Jongh]

Hi All,

I am very new to solar and almost completed my installation at home, I have read through a couple of previous discussions on earthing , but still cant seem to find a clear answer.

1: Do I need to earth my PV panels on its own earth spike or is it better to connect it to the grid supplied earth?

2: Some people suggest earthing the negative of the pv panels, Should it be done?

3: I even got advice to earth the battery bank negative. Should I do it?

I dont want to stuff this up.

Any advice would be appreciated.

Thanks

Jaco

 

[Guest]

Hi Jaco, welcome.

Having been down this road, I would be as, you, very interested in the answers coming. Earthing is a very interesting debated subject.

I was going to earth my system to the ground rod of the house, wire was connected on the actual DB boards earth and I did the tongue tippy test. But I was hesitant.

When another electrician was working in the DB board a week ago, I asked him to just please do whatever test he can do, to make sure it will all be ok before I connect all the casings and frames to the earth in the DB.

It turned out there is a potential or some such on it. Somewhere, electrician recons street side, a negative was used. On my erf, all is perfect though. Sorry for the vague terms, I lost him halfway just wanting to know the solution.

Bottom line, in my case, I was advised by him to rather get a separate earth rod for panels and all the devices.

[___]

I don't know the regulations, but this is what we did on the farm in the 80s: Ground the frames to an actual spike on the ground. The point is that lightning should take the shortest route past the expensive stuff and should go nowhere close to your DB. Don't ground the battery negative.

I think I've got that more or less right based on the ridiculous requirement that you need to earth the satellite dish. That's regulation. That's always done to a direct spike in the ground. The dish installers don't do it, they aren't electricians you see, but when you want to sell you end up needing a sparkie to put in a spike.

Sent from my GT-I9195 using Tapatalk

[Guest]

52 minutes ago, plonkster said:

... you need to earth the satellite dish.

What! In NAM only or in SA too?

Reminds me many many years ago, was still in my teens in JHB, us living on Northcliff kopie, my dad built the 2nd house there after the farm house. I was standing at a window watching a storm rolling in when a lighting bolt hit the house parapet. Man, the bricks fell down on the balcony in front of me. Groot geskrik.

Years later, after having moved to CPT, I noticed when we drove on the cement bypass, that more and more lighting rods started appearing, and houses. I also noticed a few times over the years the burnt out buildings in Randburg industrial area due to apparently lightning strikes. 

I have the impression that the storms got worse over the years.

So about 2 decade later was in Melville JHB, standing outside under the roof, having missed lighting and thunder in CPT. Just stood there enjoying the infamous highveld thunderstorm. Next moment a big bolt of lightning hit something about 200m away, thunder was instantaneous ... it was indescribably, everything inside me, liver, kidneys, heart, lungs vibrated from that raw sound. The power was ... I have no words.

Yeah I also heard a lightning strike in CPT, 1-2 houses away, was loudish but puny compared to the last one I experienced in Melville.

My point, ja, I must stay away from lightning, although it makes sense to try and limit the damage from lightning, if lighting hits, it is over. Done. Dusted. Especially on the highveld.

[___]

11 minutes ago, The Terrible Triplett said:

What! In NAM only or in SA too?

All metal fixtures needs to be earthed. That is what I was told.

I wasn't on the farm the day when the lightning took out the inverter, but word reached me at boarding school before my dad even arrived in town. It was a MSW inverter, a 1.5KVA. It was built in Windhoek, I believe the company was called Eltec or something. That was a seriously good inverter for it's time, had a big old Iron Transformer in the bottom of the case. That case probably measured 800mm tall and a good 600mm wide... well perhaps that's just how I remember it seeing as I was 12 at the time, but it was so double the size of even a 10kva multiplus :-)

Anyway, so here is how that happened. The lightning struck the phone line some distance away (old crank phone system). From there it jumped onto the roof of the house, and from there on the 36V DC lines used for lightening. From there it ran all the way into the engine/battery room and jumped from battery pole to battery pole, blowing the inverter on one end and the solar charge controller on the other end. There were burn marks in several places to suggest this version of the story is likely true. That must have been one almighty strike though: considering how far it went!

Back then that inverter was around 5k new. Imagine that. It was such a lot of money, my dad had it insured, and so it was repaired.

That was actually the second inverter: The first one was branded "Setek". Some years later he upgraded to a Nelson Adams True Sine Wave inverter. That inverter was somewhat of a disappointment: It would pick up this harmonic oscillation at certain voltage/load/temperature combinations, and then you could literally hear it go wah-wah-wah if you stood next to it, so someone in Windhoek fitted older circuitry to it to make it stop doing that. PWM was just coming into vogue back then, I suspect that inverter missed out on some proper QC or something. I have no idea what happened to oubaas Adams though. He used to operate out of Brackenfel area, and he loved to place ads in the paper and the Landbouweekblad containing bible verses :-)

[Jaco De Jongh]

@ TTT , I can relate to your feeling, just 3 short stories of my experience with lightning.

1: I bought my first house many moons ago in Valhala Pretoria. One day a storm started rolling in and I went and stood on the front stoep to watch it, next moment I just saw one hell of a bright flash and instantaneously heard this unbelievable load bang, never heard something that loud in my life before. wanted to run, but did not know where to run to. Came to my senses and realized the power was off, went to check the DB and on my way there I smelled something burning. Got to the DB and found the earth-leakage tripped, tried to reset but no luck, went through the normal drill of switching everything off trying to find the faulty circuit, but still no luck in resetting the earth-leakage. Started investigating and found 2 steel conduits to light switches shot right out of the walls. That was when I realized that something bad is going on. long story short, geyser element gone, wires to geyser and most of the light circuit wiring was fused to the inside of the steel conduit, earth-leakage was fried. Could replace most wires but in some areas we could not remove the old wires from the conduit so I had to run surface piping or chase open the walls and replace the pipes as well. Took a week or 2 to repair.

2: I had to replace a Gate motor for a client in Fourways area about 5 or 6 times in the span of a couple of months, we got worried because we could not determine what is causing the motors to pack up. I have installed lightning arrestors in all the Db's  on the farm and still the motor did not last 2 weeks. One day I was testing a motor minutes after I replaced it again when I heard something strange, almost like a guitar string vibrating. I looked around and saw blue sparks come running down 2 strands of a 18 strand free standing electric fence. I saw it from more than a 100 meters away and it was coming in my direction fast. I moved away from the motor as the post where the motor was installed was the end of that fence. It ran up to the end post and jumped right over to gate motor..... and I had to replace it again. Well at least the riddle was solved. I installed a well earthed metal plate between the gate motor and the end post, and never had to replace the motor again.

3:February 2007 while visiting my Sister on a farm close to Vaalwater, I just got out of the swimming pool and went and sat down on a steel chair in their very spacious open living room area. She was sitting a couple of feet away with her daughter on her lap, the next moment I felt the extremely  painful electrical shock, I can remember thinking to myself, "what the hell, I am not touching anything, this is impossible." I tried to scream " Help me i am shocking", but could not do a thing.  All went black for a moment and the next thing I remember I was sitting on my knees on the floor and my sister standing on the other side of the room shouting over and over :"there is flames coming out of his hand". My brother in law helped me up and told me they thought there was an explosion, but then realized it was lightning. The flames I found out was actually a spark that jumped from my little finger to the ground. I did not hear the thunder, didn't even know about it. I was in a lot pain and left for a doctor. They made the conclusion that the lightning bolt, or a part of it, must have came through the roof , entered my body on my right shoulder blade and exited through my little finger. One last very strange fact of that day. It was a beautiful clear blue day as far as the eye could see, except for this one small WHITE cloud right above the house. If it was a storm, or some dark clouds I would understand it better, but this one cloud, just didn't make sense. I was left with partial use of my right hand and constant spasms in the right side of my upper body, but luckily for me,  with a lot of medication and a lot more physio, everything was back to normal about 7 months later.

Ive got serious respect for lightning, I try to stay away from it as far as I can.

[Weasel]

There are many contradictory opinions and according to some people "regulations" when it comes to earthing. First ill say what i think you should do:

• Don't earth the negative of the panels, this will connect the circuit of charge controller or mppt to the frames and in doing so increase the likelihood of damage in the event of a lightning strike. 
• Don't earth the negative of the batteries,  same as above and this could damage your inverter.
• Earth the panels with a separate spike, the wire has to be of a similar or thicker gauge wire than what is used for the pv circuit. According to regulations the wire should connect to each panel (although i think this is ridiculous). recommend to take the shortest path to the earth spike with no sharp bends.
• if you do decide to link the grounds use thin 1mm wire from the spike to the earth of the premises and put a 1A quick-blow fuse in line (not that it would make much of a difference). but this whole point is really unnecessary in my opinion.  

Now just so we can get on the same page.. Earthing in AC circuits is for safety, if current flows into the earthing circuit the earth leakage will trip. so lets say wires start heating and burning, melts through insulation, either L or N touches E Bam it trips, or another scenario you are fiddling inside an electronics gadget and you accidentally touch live, luckily your arm also touches the case of said gadget and bam earth leakage trips, you'll get a jolt but likely survive. nowadays an RCD is able to detect leakages without current flowing through the earth circuit, it essentially detects current is missing, anyways.

in a lightning ground what we are doing is diverting a massive surge of power away from expensive stuff and ourselves. makes sense right, and that is all we are doing when we earth panels.

now for the rants:

I've had guys fight tooth and nail that all earths needs to be connected to one-another and yes that is a regulation but they cant explain why. The point here it is that this is a lightning ground. it makes no sense to make your panels part of your leakage detection circuit, if you touch say 600V DC output on your roof there's no EL that will trip... more importantly if you had a lightning strike, every piece of earthed metal is now at lightning potential, where it could have been safely or at least partially diverted. "OK but what if there's burning wires on the charge controllers input?" same issue, what will it help if your EL trips in that scenario, the panels will still work and make fire. Another argument is that the Grid has a much better earth, and yes of course, but a million volts doesn't really care if you're a tree or a copper rod. i've had a shock from a metal frame when lighting hit about 200m away, why? because its all earthed giving it a much further reach before its dissipated. A spike may not have as low of a resistance as the grid but the energy should for the most part dissipate there. Any more that does get into your grid is much better handled by lightning protection and by extension the grid earth. 

 

 

[Guest]

Jaco, best you and I stay far away from each other ... we seem to be "connected". 

[Chris Hobson]

Earthing has two separate components.

1.  Grounding of neutral.   Initially electrical systems were ungrounded but over-voltages were a problem caused by static, surges and lightning amongst other things. The solution was to ground the system. Here is a short video to demonstrate grounded and ungrounded systems. The problem was now there was a real danger that someone's body would be a conductive pathway via the earth back to source for stray current. This only occurs in ungrounded systems once there are two faults to ground. However, the nature of an ungrounded system is that the first fault can go unnoticed. It usually arcs adding to the over voltage dilemma.
2. The solution was the introduction of the earth/ground wire,  a highly conductive alternate pathway for stray currents NOT to ground but to source (Eskom or generator, invertor etc.). 

Component earthing like satellite dishes, solar panels is a completely different exercise. Here is the earthing of my panels using earth clips and the wire then runs to a earth spike.

Inside my combiner box the feed from the panels is connected to a lightning surge protector that is designed to fail closed.

 

[Janma]

7 hours ago, Weasel said:

I've had guys fight tooth and nail that all earths needs to be connected to one-another and yes that is a regulation but they cant explain why.

When it comes to lightning there are more than one way that it can damage equipment and people. I think all of us know about the direct strike between the clouds and the top of trees/houses or whatever. The reason there is a strike is there is a potential/voltage difference between two points (the cloud and the tree). Normally air is a very good insulator that prevents current from flowing, but there comes a point where the voltage difference is just to big that even air can't prevent the current from starting to flow. The amount of current that flows when this happens is enormous! You are talking kilo/mega amps flowing for a fraction of a second and then stops.

When current flows it causes an magnetic field to build up around it (this is what happens in a transformer). Now imagine how strong that magnetic field is when such a large current flows. The closer you are to the actual lightning bolt the stronger that magnetic field. If you have a conductor in that magnetic field and the field does not change nothing will happen, but when the magnetic field changes in strength or direction, it will induce a current/voltage in any conductor in side the field. This is how a transformer works. The current through the primary winding changes (AC) and that causes the magnetic field in the transformer core to change. The changing of the magnetic field causes a voltage/current to flow in the secondary coil even though its isolated from the primary coil. (Induced current will flow).  Those old iron core transformer based welding machines is a very good example of how strong an induced current can be - we weld metal with it...

Now lets see what happens when you have two earth circuits in your house that are not bonded together. The first is your normal AC earth that is connected to the grid earth. The second consist of an earth spike that has a wire running up to your PV panels. The key here is they are not connected. Now lets assume there is a lightning strike very close to your home, it causes a very strong magnetic field for a brief moment. This induces a voltage across the AC earth wire as well as a voltage across the PV panel earth wire. The voltages will NOT be the same (magnetic field is not the same everywhere and the wire lengths are not the same either).  There may be quite a big difference between the two (anything from a couple of volts to a couple of thousand volts or even higher). If someone were to touch the PV panels and the AC earth at that time, they may not be able to tell you how about how it felt afterwards...  The same applies to an inverter or charge controler that is in close proximity (electrically speaking) to the AC earth and the PV panel earth. If the induced voltage difference between the two earth systems is high enough it may find/make a path from the one to the other. That path can be via a cutter, inverter, or a person. 

Connecting the PV Panel earth, to the AC earth gives induced lighting voltages a controlled route through which to dissipate. Its better for that induced current to run via the wire connecting the two earths than through you or your equipment. That is the reason why you should ALWAYS make sure all the various earths are connected.

8 hours ago, Jaco de Jongh said:

They made the conclusion that the lightning bolt, or a part of it, must have came through the roof , entered my body on my right shoulder blade and exited through my little finger.

If it was a direct strike, you most likely would not have survived it. I might have been an induced strike as I've described above. The fact that you were wet (just out of the pool) and you were sitting on a metal chair made you a good conductor. If a lighting strike were very close it would have induced a current flowing through you and the chair. You were very lucky!

[Chris Hobson]

Hi Janma

If you have a interconnected earth system it must only have one (or one set of earth spikes or grid). If the earth spikes are scattered a lightning strike sets up a earth potential gradient and current will flow up one spike through you equipment and down the other spike as this will be the path of least resistance.

 

[Janma]

14 hours ago, Jaco de Jongh said:

1: Do I need to earth my PV panels on its own earth spike or is it better to connect it to the grid supplied earth?

Jaco I would suggest doing both. Have a wire running from the panels directly to an earth spike then have a separate wire connecting the earth spike to the AC earth in your DB as well.

14 hours ago, Jaco de Jongh said:

2: Some people suggest earthing the negative of the pv panels, Should it be done?

3: I even got advice to earth the battery bank negative. Should I do it?

Nope, I would not do that unless the inverter/charge controller's documentation explicitly instruct you to do so.

[___]

11 hours ago, Jaco de Jongh said:

They made the conclusion that the lightning bolt, or a part of it, must have came through the roof , entered my body on my right shoulder blade and exited through my little finger

I have an alternative suggestion: Eddy Currents. This ties in with the chair you were sitting on.

Physics: If you have a change in magnetic flux, any conductors in the immediate vicinity will have a current induced in them. This is why there is a rule that when using steel conduit, you must have both wires running in the same pipe (because the one cancels the other), otherwise the AC current (which produces a constantly changing magnetic flux around the wire according to the so-called right-hand rule) will induce current in the pipe.

In the same way, a lightning strike causes a small EMP wave when it strikes, and that induces eddy currents in all nearby conductors. I lost thousands of rands of network equipment once when lightning struck the building (6-story, so it likely had a steel core holding it up) and the little EMP wave induced currents in all the network wiring. I also lost a Modem (when we still used those) one day when a nearby lightning strike induced a spike in the overhead phone line. This I know because if it had been a direct strike, I'd have lost the computer too.

So back to your chair: It's possible that eddy currents induced in the chair is what got you. It's a wild guess, may or may not be the case. I'll just say I've seen a lot of damage from those things.

[___]

Second comment on earthing of the negative. Some things to understand.

1. On some inverters, usually the cheaper MSW ones, there might not be complete isolation between battery and grid. Remember also that neutral is tied to ground in your DB board. This happens with your so-called "transformerless" inverters, which has a non-isolating boost stage, or for the high-end GTIs (SMA et all), uses a high input voltage so no boost stage is necessary. With those inverters, your negative DC side ends up being connected (via the power electronics) to either live or neutral depending on what side of the AC-waveform you're currently producing. If you earth the negative, you literally short out the one bank of power FETs in the inverter.

2. Some inverters already ground the negative.

3. Charge controllers often have their current sensing in the negative line. If you ground both the battery and the PV line (or the inverter grounds the battery), you have just bypassed your current sensor and the MPPT cannot work properly.

Grounding is about picking up stray currents and shutting it down so you don't kill people. Your battery bank is at a fairly low voltage and unlikely to do that, so I see little point in grounding unless the inverter maker tells you to, and plenty of potential to severely f... things up if you don't know what you are doing :-)

Some video material, American grid, but still topical:

 

[Guest]

1 hour ago, Chris Hobson said:

Inside my combiner box the feed from the panels

Nice touch on the picture. Green power with a green leaf next to the combined box. I like.

@Janma, thank you! Any comment on my post ito the electrician picked up that on my DB's earth, that Eskom used negative in the street to earth. Will it affect my panels, solar metal casings if I was to connect all to the house earth spike direct?

Do I have to use 2 earth spikes or can all be connected to the one house earth spike?

[Jaco De Jongh]

Thanks to all who took the time to answer my first question. 

My conclusion: Earth all panels to frame, Earth frame to proper earth spike( Only One) and to supply earth. Install a 2Pole 170VDC 40kA 8/20 Surge arrestor for PV and also connect to the same earth.

Thanks again all. I already bought what is locally available in Phalaborwa, and ordered the rest from far.

Will place some pics by end of weekend if all goes well.

Some more questions to follow shortly.

[Janma]

2 hours ago, The Terrible Triplett said:

Any comment on my post ito the electrician picked up that on my DB's earth, that Eskom used negative in the street to earth. Will it affect my panels, solar metal casings if I was to connect all to the house earth spike direct?

We all know that in SA there are two types of electricity supply. Single phase and Three phase. What most people don't know is that when it comes to how the "earth" is supplied there are also different ways. (All legal and above board). One of which is tapping a wire off the neutral and supplying it as a earth wire to the consumer.

When you have a 3 phase power supply you will have 4 (or 5 wires) coming from the municipality. 3 of them are the live phases, one of them is Neutral. The three phases (live wires) will have 230 Vac relative to the Neutral wire. Remember Voltage is always measured between two points. In this case a Live phase wire and Neutral. In the distribution network the Neutral is always considered as the reference voltage (0V). But by convention the Earth (the planet) can also be used as a reference voltage 0V. It would be a very bad thing if the Neutral wire would be at a much higher voltage than the earth... So what Eskom does is they earth the neutral wire that come out of the generator. They also earth the neutral at various points in the distribution network. This is to ensure that the voltage difference between neutral and the real earth is very close to 0V. So in theory there is nothing wrong with splitting the Neutral wire into two, one they give you is labeled earth and the other is labeled neutral. (This is fine because the neutral is suppose to be earthed further up stream in the distribution network.) In an ideal world this would be the end of the story.... but..

Here's a little test you can do. Take a volt meter and switch it to measure mV. Now take the two leads about a meter apart and see what it measures. It will most likely never be 0V. The further apart the two points you measure the higher the voltage can be..  Depending from how far you are from the point where they earthed the neutral and how well its earthed you may find that there is a voltage difference between the Neutral and the real earth at your property. Typically this should be a small voltage difference.

The thing that really mess things up is when they steal cables.. If they break the neutral cable before they break the live cables you can potentially get hundreds of volts on the neutral wire and serous voltage differences between a given live and neutral wire!  This is because breaking the neutral cable they've effectively disconnected it from the ground.

In many cases (such as yours) the earth wire that you get from the municipality is nothing other than the Neutral wire. In addition to them bonding it to the earth, it is also connected to all the metal fittings in your house and all the other houses, all these fittings are connected to the earth really, so they all pull down the voltage of the neutral/earth back down to 0V relative to the earth. The problem comes in when its not done this way and the neutral is not bonded to earth properly in the distribution network...

If your sparky picked up that there is a high voltage between the earth/neutral supplied by the municipality/eskom and the real earth it could point to a wiring fault on the local distribution network. If I were you I'll contact the municipality and ask them to check it out.

Normally your appliances (inverter, fridges etc) would not be affected. They only really use the live and neutral to operate, they only care about the voltage difference between those two wires. The problem comes in with the earth wire you get from the municipality, if its connected to the metal casing of the fridge for example and you touch it you might not like it very much.

In theory the earth you get from the eskom/munisipality should be at very close to 0V relative to the earth and it should be perfectly acceptable to use it in your DB and for grounding your PV panels etc. It should be okay to connect it to your own earth spike as well. In your case I would not do that until the municipality had a look at why the earth/neutral is at high voltage.

 

[Guest]

I am onnit. Thank you @Janma.

[___]

I still don't think the solar panels should be earthed to the DB. you want lightning to go to the earth spike, not into the db where it can jump to all sorts of other places. I suppose the reason why you might want it earthed in the DB as well is in case somehow your AC power makes it it out backwards via your DC line via some kind of leak somewhere and energizes the frame. On my DC battery system that's going to help absolutely nothing!

Edit: Also, on the high voltage DC setups used with "transformless" GTIs... I'm a lot more scared of the 450VDC than the reverse-leaked 230VAC (RMS) :-)

[Guest]

Jip, I had the wire in the DB, never connected it, then had it removed. 

In MY case the earth spike is in the braai room. Used to be outside the house, till we roofed it. Currently it is sticking out above the concrete slab with tiles on top.

So in effect the spike is this side of the wall, in the ground with concrete around the top part, distance about 1.5 from DB, that is on other side of the wall.

If I can sort the problem re. the volts, then I will connected the frames and metal casings direct to the spike "outside" in the braai room, behind the washing machine. 

Truth be told, if lightning is the cause of catastrophic failure, I really do not care. Insurance Co's can worry about that.

[Janma]

8 hours ago, Chris Hobson said:

If you have a interconnected earth system it must only have one (or one set of earth spikes or grid). If the earth spikes are scattered a lightning strike sets up a earth potential gradient and current will flow up one spike through you equipment and down the other spike as this will be the path of least resistance.

Hi Chris,

I agree. You are talking about a ground loop. These can pose a serious problem. You do not want multiple paths to the ground which will cause a loop. Yes any lightning strike close to it would cause a current to flow in the loop, frying any equipment in attached in the loop.

Lighting will induce a current in any conductive loop within the magnetic field flux. In my case I have a rater large irrigation system with a central controler. There are wires running from the controller to all the irrigation valves. These + & - wires form loops from the controller to the valve and back, very narrow ones but still they are loops. Any magnetic field flux through that loop will cause current to flow through it. But there is a trick, if you twist the wires around each other and you look at them from the side you'll see that that some places the + wire is on top and the - at the bottom, then other places the - will be on top and the + at the bottom. This will work like small loops. 50% of the loops will have the + wire on the top and the - wire at the bottom and 50% of the small loops will have the - wire at the top and the + at the bottom. Depending on the direction of the magnetic flux it will cause a current to flow either clockwise through the loops or anti-clockwise. But since the 50% of the loops are one way round and 50% the other way round the current cancel each other out. They use the exact same principle in Ethernet cables (twisted pair) to minimize interference of induced currents.  

[Guest]

2 hours ago, Janma said:

You are talking about a ground loop. These can pose a serious problem.

I have another questions. How do the electricians sort the problem with houses close to one another, in cities, ito ground rods close to one another?

[___]

4 hours ago, Janma said:

Depending on the direction of the magnetic flux it will cause a current to flow either clockwise through the loops or anti-clockwise. But since the 50% of the loops are one way round and 50% the other way round the current cancel each other out. They use the exact same principle in Ethernet cables (twisted pair) to minimize interference of induced currents.  

I knew they used it in ethernet cables, never realised it's this principle. Physics 101 (or rather 144 in my case) said use the right-hand rule, that is if the current flows in the direction your thumb is pointing, the flux runs around the conductor in the direction of the other 4 fingers. I cannot remember if it was electron or conventional flow though... would have to look that up :-) Any two wires running close together with opposing and equal flows should cancel out, but I suppose twisting them together just gets them that much closer :-)

[Weasel]

11 hours ago, Janma said:

Now lets see what happens when you have two earth circuits in your house that are not bonded together. The first is your normal AC earth that is connected to the grid earth. The second consist of an earth spike that has a wire running up to your PV panels. The key here is they are not connected. Now lets assume there is a lightning strike very close to your home, it causes a very strong magnetic field for a brief moment. This induces a voltage across the AC earth wire as well as a voltage across the PV panel earth wire. The voltages will NOT be the same (magnetic field is not the same everywhere and the wire lengths are not the same either).  There may be quite a big difference between the two (anything from a couple of volts to a couple of thousand volts or even higher). If someone were to touch the PV panels and the AC earth at that time, they may not be able to tell you how about how it felt afterwards...  The same applies to an inverter or charge controler that is in close proximity (electrically speaking) to the AC earth and the PV panel earth. If the induced voltage difference between the two earth systems is high enough it may find/make a path from the one to the other. That path can be via a cutter, inverter, or a person. 

Connecting the PV Panel earth, to the AC earth gives induced lighting voltages a controlled route through which to dissipate. Its better for that induced current to run via the wire connecting the two earths than through you or your equipment. That is the reason why you should ALWAYS make sure all the various earths are connected.

Thanks, I think we do understand the immense power in a lightning strike and everything that goes with it, and it is a proper valid point you raise but truthfully not limited to earthing points wouldn't you say? like your window frame you maybe sit next to is not grounded. Now I am far more likely to be in between that and an earthed socket at my feet than be in the roof between my panels and some ground point.. its a good theoretical point but i think the reality is more circumstantial.

[virge]

Hello all,

I would like to share my experience about earthing. My install has 12x 300W Yingli panels fitted on the roof on an aluminium mounting system. The panel earthing is done in one point on a huge rectangular copper bars network spread allover in my backyard and buried at 1 meter depth. The combiner box is almost the same with the one Chris has only better, having fuses on the  - side of the strings also and a DC circuit breaker on the supply line to the house.

When disaster strikes nothing helps. I had a direct lightning strike on the roof where the panels are. It was a continuous lightning strike which lasted more than 10 seconds. The roof looked like it was on fire. The surge arrester in the combiner box simply exploded, all 8 fuses for the 4 x strings were blown, the circuit breaker in the combiner box was tripped. The result: all panels damaged, combiner box blown, the 100A fuse on the battery supply blown, inverter (Axpert 5KVA) beyond repairs. This is for the Solar Power system, in rest a lot of other stuff: energiser, gate motor controller, router, 2 computers and so on. Total damage all in all R 115,000.00.

As about having peace of mind for being insured you will find out that it is not quite so. I have lightning cover with a big name company but after the first assessor was busy with my case for a week and a half and after being chased to get fault reports for all the damaged goods (it took me a week), with specifications of the reason of the damage being lightning, the claims manager takes the case away from the initial assessor and appoints a mobile assessor to the case. I still have to be contacted by this mobile assessor. I keep phoning the insurance and complaining but nothing happens.

Thanks for reading

Virgil