Observatory Lightning protection - advice, please

[Bukko]

I am lucky enough to have built a permanent observatory in the garden. It is maybe 25m from the house but the mains cable is more like 50m long.

The cable is buried and the supply distributes to the scopes from the warm room. Separate MCB's are installed, as well as an RCCD. The Obby earth is derived from the house ground, so about 50m away.

A couple of years ago, I had a close lightning strike, perhaps 200m away. Following that, one of the PC's failed, along with one of the CCD cameras. Everything also goes through UPS's as well.

Anyway, I have been looking that a possible solution would be to install a local ground system and disconnect the earth from the house.

I have half a dozen, metre long ground spikes and my plan is to bury them around the immediate area. Interconnect with copper wire and then connect into the mains, replacing the existing ground.

I am concerned that improving the local ground connection might attract a strike. I live on the top of a lazy hill and around twenty tall trees in the vicinity.

Is there anyone out there who can advise if I am possibly going to make it worse?

Many thanks, Gordon.

 

[Bubbles82]

Hope can offer a little help,As an electrician I’d suggest that is going to be less than ideal and alot of effort for no real gain. Simply I would agree you could TT the cu in the observatory to give you a shorter fault path. The regs around this are strange when read up about and would suggest you have a look before making any changes that could affect you earthing arrangement back at the house .

[Mandy D]

You might want to consider an isolation transformer to do this. You then do not run into the problems highlighted by @Bubbles82. Run a two core cable from the secondary of the isolation transformer to the observatory and make the earth connection at the observatory end, tying down one side of the secondary to it. This, then becomes your neutral.

Google boat shoreline supply as this is a standard way it is done on boats.

I may have a secondhand 3 kVA 230V/230V transformer in an an enclosure with a 13 A socket on the output, if that suits you, but I am in the UK.

Edited December 18, 2023 by Mandy D

[Bukko]

2 hours ago, Bubbles82 said:

Hope can offer a little help,As an electrician I’d suggest that is going to be less than ideal and alot of effort for no real gain. Simply I would agree you could TT the cu in the observatory to give you a shorter fault path. The regs around this are strange when read up about and would suggest you have a look before making any changes that could affect you earthing arrangement back at the house .

Hi, Bubbles.

Any help/ideas gratefully accepted.

The incoming supply is sealed, so I cannot tell exactly what is inside without breaking in.

However, at the MCB's, all the earths are connected and run into the ground (3 phase + N come in from the top and no sign of a primary earth cable from the inncoming supply.) I am assuming the ground spike is buried there, rather than being derived from the  incoming supply.

Lightning protection seems to be a somewhat closed subject, with little advice available, apart from having a specialist visit to carry out a survey. I live in rural France, so not so easy.

I understand what you are saying about the house earthing arrangement, I do not intend to touch any of it and simply terminate the earth wire at the warm room seperately with an attached lable explaining it. 

A "ring" of local ground spikes would then be terminated locally instead .

My primary fault protection is frrom the RCCD, rather than relying on an earth.

I also take what you say about it being a lot of work for little gain, but the last strike took out a two grand camera and a PC, so history does say it is worth some effort.

The tall trees (15m+) are probably good lightning conductors so increasing my chances of a very local hit... My gut feel is the earthing change would eliminate the ground potential difference in the event of a local strike, so I guess I am looking for someone to shout at me NOT to do it !!

Gordon.

 

[Bukko]

5 minutes ago, Mandy D said:

You might want to consider an isolation transformer to do this. You then do not run into the problems highlighted by @Bubbles82. Run a two core cable from the secondary of the isolation transformer to the observatory and make the earth connection at the observatory end, tying down one side of the secondary to it. This, then becomes your neutral.

Hi Mandy,

Thanks for replying and the suggestion.

Tying in an isolation Tx would be quite a simple thing to do, as I just re-locate the existing L/N wires and run a new length from the MCB to the transformer.

However, I have a series of UPS's in the system now, so effectively they should do the job of an isolation transformer? I am also prone to frequent, short power outages and brownouts, so the UPS's are important to protect the systems from that too.

I am pretty sure my failure had something to do with a differential ground potential between the house and Obby. Everything is permanently connected and so maybe a little more vulnerable. When the strike happened, nothing in the house failed...

Do you think I would still need an isolation Tx, even when using a UPS?

 

Gordon.

[Carbon Brush]

I am not an expert in this field. However, there may be something useful in this contribution.

Lightning will strike at generally the highest point in the immediate area.
For example if you are walking through an open field in flat country, you are the highest point.
There is a very good argument for laying flat on the ground, or retreating to a ditch if available.
You don't shelter under a tree because it is the highest point and may be struck.
The tree may be damaged (burnt) in a hit, or current travelling in the ground near the trunk may may be enough to kill you.

If you look at churches, and other 'pre electrical understanding' buildings in the UK, you will see a flat metal bar running from the spire to the ground.
The idea is that if you get a hit on the roof, you have a low resistance path to earth.

The term 'low resistance' requires explanation.
If you have a damp wood roof, it conduts some electricity, but not very well. When there is a lightning hit, you get lots of local heating. The roof ignites. Or the tree in the paragraph above.
If you have a metal bar (low resistance) to earth, the current flows through the bar. The roof carries little current.
The metal bar has low resistance, so there is little heating from the strike.

What I'm getting at is you need to be reasonably confident you have surrounding objects that are far more likely to be struck, or make sure your observatory has a lightning conductor.
Something best assed by an informed person looking at the surroundings.
It is tempting to suggest earth rods or a mesh in the ground near the observatory and high current bonds to the obsy mains earth. But in the absence of an eye over the situation.....
I don't even know if your obsy structure is fibreglass, metal or wood.

If you get a hit on other structures, or the electrical distribution network, you can get big voltage spikes on the mains supply. Or huge currents flowing in distributed earth systems.
In the UK, our overhead distribution pylons have an earth wire at the top. Lightning hits here and is conducted to earth down the pylon structure.
Our lower voltage parts of the network are generally below ground. However, small poles carrying a few thousand volts often don't have the overhead earth shield.
In other places (USA for example) there is a lot more overhead local mains distribution - and a lot more equipment damage.
I have no idea what your local are mains distribution looks like. However, it ounds like damage from your previous strike may have been from currents flowing in the wiring.
A direct strike tends to blow things apart.

HTH, David.

 

Edited December 18, 2023 by Carbon Brush

[AstroKeith]

The surge protection provided by UPS devices is minimal and won't protect against a lightning strike. Similar an isolation transformer dosent stop ground currents.

It would appear that without a local earth at your observatory and a 25m ground path, lightning induced ground currents could be very large. The ground of your electronic equipment is almost certainly to be connected to the supply earth, and so fries.

I would recommend a high capacity surge protector in the observatory (Din rail mounted, say 40kA rating) with a good local ground.

If you have tall trees around you, the observatory is unlikely to be hit directly (unless it has an earthed metal dome!), but nearby strikes will produce ground currents. A rule of thumb is to imagine a 50m diameter sphere rolling over your property - anything touching the sphere is at risk. Do the trees hold the sphere off the observatory/

[Mandy D]

15 minutes ago, Bukko said:

Hi Mandy,

Thanks for replying and the suggestion.

Tying in an isolation Tx would be quite a simple thing to do, as I just re-locate the existing L/N wires and run a new length from the MCB to the transformer.

However, I have a series of UPS's in the system now, so effectively they should do the job of an isolation transformer? I am also prone to frequent, short power outages and brownouts, so the UPS's are important to protect the systems from that too.

I am pretty sure my failure had something to do with a differential ground potential between the house and Obby. Everything is permanently connected and so maybe a little more vulnerable. When the strike happened, nothing in the house failed...

Do you think I would still need an isolation Tx, even when using a UPS?

 

Gordon.

A UPS can act as an isolation transformer, but it will depend on the type and how the wiring is connected internally. If it is a line interactive type, it will not be using a transformer when mains is present, only when running from the batteries. With an online UPS, there will generally be two transformers, one feeding the battery charging and the other on the inverter side. The charger transformer also runs the inverter when mains is present, so you have double isoltation. However, they always earth the secondary of the inverter transformer down to the incoming mains earth, so you will have to open up the UPS and break this connection, then make your own connection to the local earth rod network. It can be done, but means messing with the internals of the UPS.

[Bukko]

Hi David, Keith and Mandy.

Thanks for the extra input. Attached is an overhead of the house and observatory.

Buildings, all three are on concrete with a vapour barrier. Warm room is wooden. The domes are elevated fibreglass on a brick "wall" 0.5m and 0.8m high. Internal metal piers are on their own concrete footings.

To help with the scale, the corner of the house to the nearest corner of the warm room is just under 20m. Orientation, North is to the top. The trees to the north of the Obby are 15m+ high, many of the others vary from 5m to 15+, so plenty of conductors. As I said, I am located on relatively high ground.

I thought I would have more protection from the UPS's. A decent surge protector sounds like a good idea for the whole house. I am looking into fitting some solar panels sometime soon, to reduce my electricity bill. (Electric heating...) So adding one when the supplies are merged would be easy. I did actually consider powering the Obby with a couple of solar panels and battery backup; maybe if I did this, I would not have had the failure. Hohum.

David, our supplies are low voltage on little pylons. It is all being upgraded with an new external earth at the top, so hopefully this will help as well although still overhead. To balance that, we are soon to get 2GB fibre connections direct to the house, so not completely prehistoric.

Keith, on your explaination of the trees, yes, they are much closer than 50m. I cannot see evidence of lightning strikes on them, but history does not guarantee the future. And yes, I expect it would be a local strike, rather than a direct one. After the incident, I found my insurance did not cover the domes, etc. so my loss. My new insurance covers it completely so any direct strike means an oppertunity to upgrade. However, I don't want that to happen.

 

If I can summarise the proposals, I go with disconnecting the house earth and connect up a new local earth from (I think 8 ground rods) inside the warm room distribution box.

By disconnecting the house earth, the UPS earths will now reference th elocal earth, so no need to take them apart.

I should also fit a high capactity surge protecctor in the warm room and when I fit the PV panels, fit a 3-phase one there too.

Does this all sound like a reasonable plan?

Gordon.

[AstroKeith]

Looking at your photo (nice place BTW!) I think it would just fail the 50m sphere test, so there is a chance of a direct hit but sounds like you are insured for that.

Induced currents are the problem as they will be produced by nearby strikes and even cloud to cloud discharges. The Surge protector in the warm room, plus a good local earth should stop such currents. You have a small distance between warm room and observatories but to be safer, make sure your observatory earths run back along the same path at the supply, back to the warm room earth.

8 earth rods arent needed - rather one deep one. 2.4m is usually called for.

[Bukko]

6 minutes ago, AstroKeith said:

Looking at your photo (nice place BTW!) I think it would just fail the 50m sphere test, so there is a chance of a direct hit but sounds like you are insured for that.

Induced currents are the problem as they will be produced by nearby strikes and even cloud to cloud discharges. The Surge protector in the warm room, plus a good local earth should stop such currents. You have a small distance between warm room and observatories but to be safer, make sure your observatory earths run back along the same path at the supply, back to the warm room earth.

8 earth rods arent needed - rather one deep one. 2.4m is usually called for.

Thanks, Keith. Two acres takes a whole lot of grass cutting and the pool is a great big pit that I keep throwing money into !!

Anyway, I do have some sockets so can join rods to rods for the depth.

The power to the domes are distributed from the warm room, so (local) earth will go with the power and I am surprised how cheap the surge protectors are. Would you be happy with the cheapies, or should I look for a more reputable manufacturer? ABB / Siemens perhaps??

G.

[AstroKeith]

Definitely go for quality - design is one thing, but they need to made and tested to the highest standards.

[Bukko]

2 hours ago, AstroKeith said:

Definitely go for quality - design is one thing, but they need to made and tested to the highest standards.

My sentiments entirely...

[discardedastro]

Surge protection and local earth is definitely the way to go as others have said. Couple of long earth rods will work better (and be cheaper!) than lots of short ones. The overall surface area is what you're after, coupled with low resistivity. Don't forget they need regular inspections. If you want a lower-maintenance solution then "conductive concrete" is a thing. Pretty widely used in telecoms these days for earths for street cabinets as they don't need the depth (often a problem near buried utilities!) and are maintenance-free - they can't corrode as such.

UPS-wise, definitely look for "online" topology which has the UPS constantly generating its own clean AC. As others have noted, that won't help you with surge current and it won't provide protection from lighting. However, lightning causes all sorts of fun transient currents and issues that can still cause problems for kit. Line-interactive won't respond quickly enough, but online doesn't really have to be quick because it's always on. Note some online UPSes do have an efficiency bypass mode which you'll want to disable for this sort of thing.

Edited December 22, 2023 by discardedastro

[900SL]

If you install an earth rod, ensure you check the earth resistance. From memory it should be less than 25 ohm, but check on line. There's plenty of guidance

I'm not an electrical engineer but had to deal with lightning protection on tall structures.  Everything earth bonded and straight path down,  25mm2 copper flat again from memory for tapes

Edited December 28, 2023 by 900SL

[Bukko]

A little update...

I have struggled to find ground rods in France, either I am struggling to find them in the DIY store searches, or they are not generally available to end users.

Anyway, on my last UK trip, I bought several of them and as I can't really transport stuff much longer than 1m, I got a few joiners and termination pieces.

The ground, right now, is really wet so the clay and stones will give a bit. I have a couple of SDS Plus tools, but neither made much progress. I also have a more subsstantial SDS MAX concrete breaker and trying to get the rods to 2m depth teek some effort (from the breaker!!)

So, I have a loose planting of a few rods that I will connect up and replace the existing house earthing cable to a local one.

And when it arrives, I will fit the lightning protector and hopefully, everything will be safer.

Thanks to all for the help !

 

Gordon

[Oddsocks]

Hi Gordon.

Sounds as though you are sorted now but if you need extra rods, couplers, tapes (or other electrical parts) etc then try this French supplier:

https://www.123elec.com/gamme-materiel-electrique/mise-a-la-terre.html
 

You can search the web using the term “Piquet de terre cuivré” (Copper earth stake) which should find other France based suppliers.

Never thought of using a SDS hammer drill to push the rods in myself, being rather old school I used a 14lb sledge and a steel bolt screwed into the rod coupler threads as a load spreader.
The terrain at my UK observatory was stoney river delta and it took a good hour of swinging the sledge to drive 2m rods into the ground in 1m sections, with frequent pauses to re-tighten the coupling between the first and second rod sections as they tend to unscrew themselves under the shock of being hammered into the ground.

William.

[Carbon Brush]

With clay digging you have my sympathy🤣.
When digging my garden pond I soon discovered spades and picks just stuck in th clay and it took minutes to extract them!
The solution was a petrol driven post hole borer with 150mm auger - then take away the loose spirals using shovels.

If you drill the holes larger than the rod diameter, the rods will drop straight in.
Given a little time, the clay will move to grip the rods tightly.

[Bukko]

7 hours ago, Oddsocks said:

Hi Gordon.

Sounds as though you are sorted now but if you need extra rods, couplers, tapes (or other electrical parts) etc then try this French supplier:

https://www.123elec.com/gamme-materiel-electrique/mise-a-la-terre.html
 

You can search the web using the term “Piquet de terre cuivré” (Copper earth stake) which should find other France based suppliers.

Never thought of using a SDS hammer drill to push the rods in myself, being rather old school I used a 14lb sledge and a steel bolt screwed into the rod coupler threads as a load spreader.
The terrain at my UK observatory was stoney river delta and it took a good hour of swinging the sledge to drive 2m rods into the ground in 1m sections, with frequent pauses to re-tighten the coupling between the first and second rod sections as they tend to unscrew themselves under the shock of being hammered into the ground.

William.

Hi, William, happy New Year !

Thanks for the link, for now, I am done but it is always useful to build up a good range of suppliers.

The "soil" here is heavy clay and stones. The stones range from the small to apple sized pieces and digging is next to impossible. My SDS Plus drills were almost useless. My heaviest sledge is 4kg and it is really difficult to control it, hence, the use of a bigger SDS tool. The MAX did the job, but effectively each two length rod destroyed the coupler I used inside the SDS MAX throat. If the coupler between the two rods failed, the second length would bury itself really quickly, so I am pretty sure it is 2m deep now.

As an aside, I changed the dessicaant on my ASI camera the other week.

I know you use a modified plastic box with gloves fitted and Argon purge. I got a portable glovebag and used that. Basically, a much bigger ziplok bag with gloves fitted, it is designed as a portable fume cupboard for laboratory work in the field. I used a small 1 litre welding canister of Argon, and reduced the air content to less than 10% in one go. I estimate I used less than half the canister, so pretty cost effective. I will get back to the Imaging thread and update it when I get some time later...

Gordon.

[Bukko]

7 hours ago, Carbon Brush said:

With clay digging you have my sympathy🤣.
When digging my garden pond I soon discovered spades and picks just stuck in th clay and it took minutes to extract them!
The solution was a petrol driven post hole borer with 150mm auger - then take away the loose spirals using shovels.

If you drill the holes larger than the rod diameter, the rods will drop straight in.
Given a little time, the clay will move to grip the rods tightly.

Thanks for the sympathy.

Clay is terrible. When dry, it is like working in concrete. When wet, as you say, heavy and just sticks to the spade. Stainless steel spade seems to be a bit better, though. And there is a spade, American, I think, called a "Root Slayer". It is teflon coated and a lot easier to get the clay off. It just does not pick up much soil at a time, but good to cut through the ground.

I did get a petrol auger and basically, it could not get past the heavy stones.

But I am lucky here, I am surrounded by farmers and to have access to mini diggers and someone to operate it. Usual price for assistance is a nice bottle of Scotch..

Gordon.

[Bivanus]

Hello @Bukko , in another life it just happened to have had to install a lightning arrester solution for some crude oil tanks placed in an area with a similar bad soil. What the designer did was to use a double approach: passive and active.

Passive: Similar to what you say , buried electrodes with activated zinc however placed in holes that were packed with some graphite & a salt combo to improve the overall impedance, linked by metallic strips also buried from which metallic rope went to a number of  pointy lighting arresters ( one per building ) By measurement we have had them at 0.5 - 0.8 Ohm , that is below the legal requirement of 1 Ohm. 

Active: A number of active lightning arresters place WAAAY OUT of the reservoir location. These were the spiky sphere type , Prevectron I seem to remember were called. This were the ones that "attracted" the lighting , that's why they were placed outside the perimeter. The only time I've actually saw a lightning strike was on this devices , not on the  passive ones. This type of devices have a calculated covered area that is quite large  but care must be taken to ensure a good draining path for the lighting voltage. 

Edit: I've looked at the picture , if the structure on the left is the observatory , one active lightning arrester placed between them , around the point where there is a little bush in the picture , could protect both , but some calculations have to be done to determine the pole height. Usually the companies selling the devices also have an engineer doing this or know another company who does. 

Edited January 7 by Bivanus
Aditional info

[Bukko]

3 hours ago, Bivanus said:

Hello @Bukko , in another life it just happened to have had to install a lightning arrester solution for some crude oil tanks placed in an area with a similar bad soil. What the designer did was to use a double approach: passive and active.

Passive: Similar to what you say , buried electrodes with activated zinc however placed in holes that were packed with some graphite & a salt combo to improve the overall impedance, linked by metallic strips also buried from which metallic rope went to a number of  pointy lighting arresters ( one per building ) By measurement we have had them at 0.5 - 0.8 Ohm , that is below the legal requirement of 1 Ohm. 

Active: A number of active lightning arresters place WAAAY OUT of the reservoir location. These were the spiky sphere type , Prevectron I seem to remember were called. This were the ones that "attracted" the lighting , that's why they were placed outside the perimeter. The only time I've actually saw a lightning strike was on this devices , not on the  passive ones. This type of devices have a calculated covered area that is quite large  but care must be taken to ensure a good draining path for the lighting voltage. 

Edit: I've looked at the picture , if the structure on the left is the observatory , one active lightning arrester placed between them , around the point where there is a little bush in the picture , could protect both , but some calculations have to be done to determine the pole height. Usually the companies selling the devices also have an engineer doing this or know another company who does. 

Hi @Bivanus, in my previous life, I worked in the chemical industry. A long time ago, a lightning strike on a tall distillation tower was met with a high impedence grounding. The resulting voltage spike did huge amounts of damage to the instrumentation and process control computers and shut us down for a week.

Afterwards, there was a project to upgrade the grounding system. 

According to lightningmaps.org, the strike was further south than the picture shows - perhaps up to 100m away and it took out many of the house breakers, as well as the Observatory supply.

I understand the rationale about managing the strikees, but I would prefer to find a way to prevent one even close to my stuff.

For now, I have simply driven the rods into the ground, and as soon as I get time to run the interconneccting cable, I will do resistance check to see if I am good. The ground is so wet, I am sure it is fine, so I will test again in the summer, to be sure. If I need to do something more sophissticated, I will sink something close by. I am adding enough in the wires to allow for this.

Hopefully, when I am finished, I will not suffer another hit.

Gordon.

[Birman1]

I have just seen this interesting thread and whilst grounding and arresters are sensible precautions, sensitive electronics like cameras and computers need good screening to survive close lightning strikes.  Very powerful RF fields are generated by the strike together with high static fields

I recall in the 70s a friend living in a small block of flats in London. The chip shop opposite was struck by lightning and burnt down. Most of the TVs in the flats died due to damage to their preamps whether they were plugged in or connected to antennas or not !
So think Faraday cages as well in bad storms

B