lightning protection for landscape lighting system - Page 1
Forum section: electronics / projects

author: RustyShackleford
author_rank: Regular Contributor
timestamp: July 26, 2025, 06:46:56 pm
content: I've talked about my landscape lighting system before. It uses LT3081 regulators configured as current sources, to drive multiple series-connected strings of LED luminaires. My concern now is how to provide some protection against lightning strikes (and other ESD events) creating surges in the wiring (that runs for sometimes hundreds of feet with minimal burial).I believe some combination of the following components may provide a solution: MOV (metal-oxide varistor), GDT (gas-discharge tube), and TVS (transient voltage suppressor). I've also read that a simple loop in the conductors, placed in very close proximity to the ground, can provide protection ("lightning doesn't like to go around corners").This article:https://lsp.global/knowledge-of-lightning-protection-and-surge-protection/suggests that a cascade of such devices may provide a good solution. See the image below (I can't figure out how to include it inline).So I'm imagining a solution shown in the second image below.On the left is a simplified version of one (of several) of my current source drivers that need to be protected.In the middle is a copper sheet, with stanchions to wrap the cables around in a roughly 10" diameter loop-and-a-half. It's mounted to the wall below the central controller (which contains the current drivers, etc).To the right is a tiny PCB, one per current-source driver, that'll be in a row below the copper sheet, from which the cables exit down to the earth and out to the luminaire strings.I put Tranzorb transient-voltage suppressor diodes on the two conductors coming onto the current-driver board. I selected one with 30.8v stand-off voltage. The 1N4148 is already on my boards (put to absorb di/dt spikes from hot connecting/disconnecting luminaires), probably redundant but can't do any harm.The copper sheet incorporates the "black magic" idea that "lightning can't go around corners" and also provides inductance between the Transzorbs and the MOV/GDT devices. Obviously this inductance is common-mode; it'd be a pain to separate the two conductors in the cables (which are landscape-lighting wire, basically 18awg zip-cord with extra-heavy insulation) for the loops. But the lightning induced spikes should be common-mode as well.And finally, the two MOV/GDT devices on the one-per-driver tiny PCBs below the copper sheet.In my controller (current drivers) I've kept logic ground (GND) separate from the AC mains EGC (imagining the latter might tend to be noisy). It seems that EGC would be far more robust a grounding point (GND passes through switching power supplies). But I'm measuring up to 15v of differential between GND and EGC. A 1K resistor between GND and EGC reduces this differential to 150mv or so (depending on the load on the power supply).

author: floobydust
author_rank: Super Contributor
timestamp: July 26, 2025, 07:29:12 pm
content: You have to think how the lightning surge is getting into your system. There are ground strikes, powerline strikes and cloud-cloud as well.You are proposing to protect across the DC feed which is fine and covers some of that but...Most often the transient comes in on the mains power and seeks earth ground. Lightning hitting the grid, distribution system.So it will arc through your power supply, through to a path to the best ground in town, dirt. It can depend on your home's ground rod how good that is.It's the potential difference (during the transient) between powerline neutral/ground and the actual earth ground your landscape lighting is very close to.This is where I see many product fails.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 26, 2025, 08:13:52 pm
content: In the UK, telephones lines (which are 2-wire) in lightning-prone areas were protected by a pair of gas discharge tubes connected between each wire and a local ground. They were only intended to protect against induced voltages, not direct hits, but they really did make a big difference to the number of line faults. Key to that was the automatic recovery of the tubes after the event. They were pretty robust devices.There was a cheaper device available which was a slide-in replacement for the gas discharge tubes. I don't know what was inside them, but once they had "flashed over" they stayed conductive. So although they did reduce the amount of damage to the phone line, they still needed an engineer callout to replace them.I don't know if gas discharge devices are available these days, but it might be worth looking into. Their robustness and automatic recovery might make them more appropriate than semiconductor-based (or similar) devices.

author: RustyShackleford
author_rank: Regular Contributor
timestamp: July 26, 2025, 09:45:11 pm
content: Quote from: floobydust on July 26, 2025, 07:29:12 pmIndeed, I believe the recent event (which caused me to move this project to the front burner) probably did occur via the mains power. Because, the damage was to the Arduino in the control controller and to the LT3081s in the circuit boards there. The strings of luminaires werecompletelyun-harmed.But I feel like my home's AC is reasonably well-protected. I have this surge suppressor on the main load center:https://www.homedepot.com/pep/Eaton-108kA-Whole-Home-Surge-Protection-Device-CHSPT2ULTRA-CHSPT2ULTRA/204761136?g_store=&source=shoppingads&locale=en-US&pla&mtc=SHOPPING-BF-CDP-GGL-D27E-027_008_CIRCUIT_PROT-NA-NA-NA-PMAX-NA-NA-NA-NA-NBR-NA-NA-NEW-NA-Priority2024&cm_mmc=SHOPPING-BF-CDP-GGL-D27E-027_008_CIRCUIT_PROT-NA-NA-NA-PMAX-NA-NA-NA-NA-NBR-NA-NA-NEW-NA-Priority2024-20420576520--&gad_source=1&gad_campaignid=20420577051&gbraid=0AAAAADq61UfQRFnecHfpj2Z0qImOvJB6V&gclid=Cj0KCQjw-ZHEBhCxARIsAGGN96IdL0wfVbwfwaPnKRL8selMKdsmcPzc78Uc7YQ62oa6Vayv3jpnSDoaAorvEALw_wcB&gclsrc=aw.ds... and a couple of 8ft ground rods (plus two more, one on the ground-mount solar panels, and one by the shipping container workshop). I guess I need to add something more where the AC enters my controller - some configuration of the afore-mentioned devices. Perhaps as simple as a higher-voltage selection of the TVS I proposed using on the DC conductors:https://www.vishay.com/docs/88369/p6ke.pdfBut I do find it a mite counter-intuitive that this is a more likely culprit than the DC conductors in the strings of luminaires. Being rural, I have a dedicated transformer, and the conductors between it and the house are buried. In fact, the 7.2kV primary is also buried when it gets to within about 1000ft from the transformer.

author: RustyShackleford
author_rank: Regular Contributor
timestamp: July 26, 2025, 09:48:36 pm
content: Quote from: SteveThackery on July 26, 2025, 08:13:52 pmWell, I'm thinking some combination of the two, as described in the paper linked in my OP. One of the devices I plan to use contains an MOV intergrated with a tiny GDT:https://www.eaton.com/content/dam/eaton/products/electronic-components/resources/data-sheet/eaton-movgt-integrated-mov-gdt-device-data-sheet-elx1161-en.pdf

author: floobydust
author_rank: Super Contributor
timestamp: July 26, 2025, 10:25:45 pm
content: I'm not sure when you got the Eaton surge protector - before or after the Arduino got killed? Did its power supply also get killed?You can have all the surge protectors in the world but they require a decent local ground.If the ground rods or their wiring is corroded, or the soil is dry, or is rock etc. you can think it's all good- when it isn't.At least one ground rod needs to connect to the building service.Lightning transients can also come in from solar arrays. That is yet another path I have seen.Gas tubes are a bit slow but still high activation voltage - so say 300V is a bit too much for your LEDs.

author: RustyShackleford
author_rank: Regular Contributor
timestamp: July 27, 2025, 02:22:21 am
content: Quote from: floobydust on July 26, 2025, 10:25:45 pmI installed the surge suppressor a few months ago when I replaced my load center; landscape lighting damage was last week. There's still two green lights on it, so I assume it's happy.QuoteAre you saying you feel that's the main culprit in the recent damage ?QuoteThey're all connected to the building EGC, including the "remote" ones.QuoteThat's easy to believe.QuoteThe idea in the paper I linked (and 1st image in my OP) is that they're part of a sort of cascade of protection:When the surge voltage is applied to the input terminal of the protection circuit, the transient suppression diode TVS with the fastest response time first operates. By selecting appropriate coupling component (inductor or resistor) parameters, the circuit is designed to allow for an increase in discharge current before potential damage to the suppression diode occurs, so that the voltage drop generated on L2 plus the voltage drop on TVS reaches the breakdown voltage of MOV, at which point MOV starts to discharge. Similarly, as the discharge current further increases, it causes an increase in voltage drop on L1 plus MOV’s breakdown voltage to reach GDT’s operating voltage, ultimately releasing a larger surge current through GDT ...

author: RJSV
author_rank: Super Contributor
timestamp: July 27, 2025, 04:47:04 am
content: Personally, I'd go with the advice, from an early post here (floobydust) that you are looking probably at a ground to ground surge, incoming ground, to the 'dirt' contacting rod(s). A headache for sure, but I admire the attempts, as these things can be very non-intuitive !

author: Kjelt
author_rank: Super Contributor
timestamp: July 27, 2025, 07:17:44 am
content: I have reversed engineered the mains protection circuitry of an outdoor HID bulb driver about twenty years ago.You have to adjust the VDR values and fuse rating to your local mains voltage and load.

author: RustyShackleford
author_rank: Regular Contributor
timestamp: July 27, 2025, 03:59:57 pm
content: Quote from: RJSV on July 27, 2025, 04:47:04 amSo you're saying poor connection from house's EGC to the ground rod ?

author: RustyShackleford
author_rank: Regular Contributor
timestamp: July 27, 2025, 04:03:59 pm
content: Quote from: Kjelt on July 27, 2025, 07:17:44 amLooks like you're in the Netherlands, where it appears power is 230vac but no split-phase like in USA. So X1-1 and X1-3 are the "hot" wires and X1-2 is ground ? And component SG1 is a GDT ?Looks like this will help with the incoming AC. I'm also tempted to put Transzorb TVS devices on the DC power supplies in my controller: 30vdc for the series-connected strings, 12vdc for "legacy" landscape lighting fixtures, and 5vdc (derived from 12vdc with a DC-to-DC converter) for the Arduino and other logic.But of course all this depends on a good ground connection.

author: floobydust
author_rank: Super Contributor
timestamp: July 27, 2025, 05:28:10 pm
content: Ponder this. Your landscape lighting system is powered off say a car battery. How do lightning transients get to it?

author: Zero999
author_rank: Super Contributor
timestamp: July 27, 2025, 06:21:38 pm
content: Quote from: floobydust on July 27, 2025, 05:28:10 pmTransients can be induced.I had some solar panel on top of a metal shed roof, charging a couple of SLA batteries, via an LM317 to limit the voltage. The LM317 would often blow, until I put a 33V zener diode across it, which solved the problem

author: SteveThackery
author_rank: Super Contributor
timestamp: July 27, 2025, 06:21:52 pm
content: Quote from: floobydust on July 27, 2025, 05:28:10 pmInduced voltages (and currents) from nearby lighting strikes are real, and might need managing, depending on a number of factors. These definitely affect non-grounded circuits. Of course, no realistic level of protection can withstand a direct strike to your wires.I don't know if lightning willdirectlystrike a battery-powered (so not grounded) wiring system, but my suspicion is, when you are a lightning bolt, everything looks like a ground.

author: Zero999
author_rank: Super Contributor
timestamp: July 27, 2025, 06:26:24 pm
content: Quote from: SteveThackery on July 27, 2025, 06:21:52 pmIs it even economically possible to protect against a direct strike? The only way to do that is to put a lot of effort into mechanical construction of a good Faraday cage, as well as over voltage protection.

author: floobydust
author_rank: Super Contributor
timestamp: July 27, 2025, 07:34:42 pm
content: I have seen solar panels, steel doors etc. seem to pick up a lot of common-mode voltage spikes from lightning, and think it's capacitive coupling.For moderate induced transients, I think TVS would be fine. But we don't know the length of the wiring runs. How big is the run?Second, you need coverage for transients coming in from mains.

author: Kjelt
author_rank: Super Contributor
timestamp: July 27, 2025, 07:57:43 pm
content: Quote from: RustyShackleford on July 27, 2025, 04:03:59 pmYes F is Fase Hot) and N is Neutral, PE protective earth.But that is for my home situation, as said this came from an outdoor HID driver, that was sold for outdoor conditions with lightning protection.But good to check with a US EE if this suffices.

author: RJSV
author_rank: Super Contributor
timestamp: July 27, 2025, 08:23:54 pm
content: Actually, (sorry), in my haste to post I mis-stated:Should have said that:According to floobydust account, the lightning enters via the POWER INPUT that being including the incoming ground, but then the high potential overwhelms the actual connections and 'seeks' a path (to actual 'dirt' ground, with shortest path.Likely the physics, of that, include the forming of a pre-strike path or what I've heard called a 'discharge aura' that is maybe several milli-seconds before a powerful strike, or arc.So, I'm applying my own limited experience, but not necessarily implying that the house grounding rods are corroded or defective, just the concept that the whole trouble enters via the power wire set entering the house: ground, and two phases of power, entering as a set.

author: RustyShackleford
author_rank: Regular Contributor
timestamp: July 27, 2025, 08:36:08 pm
content: QuoteYeah, I think that's a non-starter.

author: RustyShackleford
author_rank: Regular Contributor
timestamp: July 27, 2025, 08:40:33 pm
content: QuoteThat's what I'm going to do for now: throw a bunch of those Tranzorb TVS diodes at the problem. Is that enough ? No way to know until the next "event".QuoteSome of them are 300ft long, going down the driveway. Others are much shorter. (There's a number of LT3081 current-source drivers, each powering a series-connected string of LED-based luminaires. UL doesn't allow more than 30vdc with minimal burial, so limited to about 9 LEDs per driver).

author: Silenos
author_rank: Regular Contributor
timestamp: July 27, 2025, 08:56:23 pm
content: Quote from: RustyShackleford on July 27, 2025, 03:59:57 pmNo one can tell as no one here even saw your setup. Mind you, soil types and layers matters, buried materials matter, contact surface matters. Either way, you can only be sure by measuring its static resistance.Your leds would suffer at most from induced currents from faraway strikes, close or direct strike may or may not be mitigated, and it cannot really be predicted. Anyway, normal TVS between long wires and rails are an entry protection. GDT - they are normally avaliable as smd parts, could also be an option. Varistors - never seen them on long lv wires.Same with properly designed anti-lightning protection on your rooftops. Even if you have the perfect system, you can have you electronics inside house fried through induction. Or not. But at least chance for the roof catching fire from a direct strike is minimized.

author: RustyShackleford
author_rank: Regular Contributor
timestamp: July 27, 2025, 10:08:03 pm
content: QuoteThat might be worth trying, to see if I should further pursue that angle. Any tips on how ? Ohmmeter between house EGC and a metal stake driven into ground somewhat near my ground rods ?

author: PCB.Wiz
author_rank: Super Contributor
timestamp: July 28, 2025, 02:41:29 am
content: Quote from: SteveThackery on July 26, 2025, 08:13:52 pmYes, GDT still exist and are even made in SMD versionsSeehttps://lcsc.com/products/Gas-Discharge-Tube-Arresters-GDT_11196.htmlThey have impressive short term pulse handling, but not at low voltages.

author: floobydust
author_rank: Super Contributor
timestamp: July 28, 2025, 02:41:43 am
content: What I will do is first measure ACV between Neutral and Ground, should be under 1V. If it is, I'll switch to Ohms to confirm the Neutral bond is intact at the service (ground).You could measure ACV and Ohms from your electrical (outlet) GND to other grounds like metal plumbing pipes to see if things look OK.Incoming Neutral on the distribution network is daisy-chained with other neighboring houses. I forgot if this is limited to the distribution transformer or not.I'm saying your Neutral thus your local (house) PE ground are connected to other people's homes. I have seen an open ground or neutral at their house (dist lines) pump current through my own ground rod, as if I was the ground for everyone.Point is you need to confirm your house ground is low impedance and working. Otherwise the SPD cannot protect mains (Arduino and lighting PSU).

author: johansen
author_rank: Super Contributor
timestamp: July 28, 2025, 03:43:38 am
content: For direct strikes there is little hope of protection, the issue isn't just the currents involved, 50,000 amps decaying to 1000 amps after 0.1 milliseconds, but the issue is the ground impedance where the lightning strike is 1 ohm or so.Basically you have 50 thousand volts sending current down the wires you are trying to protect, even for a nearby strike.Years ago we had a 7200v line break and it arced on the ground and my sister got video of it. I do not remember our phone being destroyed, but the wire landed on top of the buried phone line and the voltage in the ground physically destroyed the phone line. and that's just 7200 arcing to the ground within a few feet. to be fair, the ground was mostly gravel and the line was probably only 12 inches deep.Ethernet wires can handle 8000 volts dc in my experience (not at the connector, but the insulation).basically you can have all the distributed grounds and gas discharge tubes you want, but the issue is that lightning has a significant dc component that will get through any inductor, and you may find your wires are going to be physically destroyed.for indirect strikes, yes you can protect from it because its only the ac components of the lightning strike that can radiate a long enough distance to get into your stuff.For a 30 volt system you can use 40 volt TVS diodes. i've been impressed by them, in one case, i had a tiny sot-123 iirc surface mount 12v tvs diode protecting a gate driver, and a 10 ohm 1/4watt resistor. it had no problem handling the 30 amps through the gate drive resistor long enough to blow it up.with enough tvs diodes you can easily handle the 1000 amps that will happen as a result of a nearby but not direct lightning strike.a standard ground rod may only be 25 ohms, so you have to ask where is the voltage going to show up at.

author: RJSV
author_rank: Super Contributor
timestamp: July 28, 2025, 04:09:07 am
content: My Lord, those last numbers indicate that, for 100 usec. 50,000 volts drives, through 1 ohm, 50,000 amps ! ??So, power being the V x I, that's 2.5 billion watts.Or = 2.5 gigawatts during that brief 100 usec.No wonder these specialists talk like philosophers, (lol) !

author: johansen
author_rank: Super Contributor
timestamp: July 28, 2025, 06:15:01 am
content: Quote from: RJSV on July 28, 2025, 04:09:07 amthat's just the power dissipated in the ground resistance alone.the rare positive lightning bolts, 10 times more powerful with currents on the order of half a million amps have been recorded.unfortunately the Fieldlines forum is gone now but not many years ago i saw photos of a lightning strike which had vaporized a buried conductor.. which meant the dude didn't need to dig a new trench to replace the line. it had been dug for him by the vaporized copper expanding plasma. --The average lightning bolt will not melt a 4awg wire.I did notice utilities are no longer wrapping the 6" by 3 foot long copper sheet around the bottom of the pole, they are now just strapping it to the side and bending it over the bottom in an "L" -which makes more sense. its half a microhenry less inductance..

author: RJSV
author_rank: Super Contributor
timestamp: July 28, 2025, 06:38:51 am
content: ...I ran a trial number, for a hypothetical case, where that 100 usec. of power, at 2.5 GW, gets spread out, in time, over 1 hour. Of course there is plenty more time, for the heat to dissipate into a lot more volume of surrounding soil, course.I just wanted to see what the numbers show. Equivalent to 1 hour at close to 670 watts. That would likely do set any standing water to boil, maybe even with normal heat dissipating into soil, over the hypothetical 'one hour'. But of course the lightning strike HEAT creation in reality does not have that dissipation process, over an hour's test, as my speculation details. Still, it gives an insight, into that 2.5 GW dump, into surroundings,...with a grain of salt of course.Rick

author: PCB.Wiz
author_rank: Super Contributor
timestamp: July 28, 2025, 10:06:31 am
content: Quote from: RustyShackleford on July 26, 2025, 09:45:11 pmWhat is the cable voltage and drop across the LT3081 and LED strings ?You may not have much headroom for TVS parts to work.The LT3081 is a slightly unusual choice, for LED drive, but I guess they are already in place.

author: RustyShackleford
author_rank: Regular Contributor
timestamp: July 28, 2025, 05:39:01 pm
content: Quote from: PCB.Wiz on July 28, 2025, 10:06:31 amShort answer: 30 volts. One side of the cable is getting the 30vdc from DC power supply (subject to a fuse and a power pfet to turn off/on) and the other is pulled down by the LT3081, to whatever voltage pulls the desired current through however many LEDs are in series.Yes, LT3081 might be an odd choice, but my whole system is odd, with the luminaires being in series.And yes, not much headroom. I'd probably use the TVS with 30.8 stand-off voltage, for which the clamping voltage is 49.9, which exceeds the 40v absolute maximum for the LT3081. However, probably only for a VERY short time. Parts are rarely characterized for such brief stresses, but I imagine there's a good chance it can handle it.

author: floobydust
author_rank: Super Contributor
timestamp: July 28, 2025, 08:15:45 pm
content: I still don't get what happened to the Arduino, what did the autopsy reveal? Is the 30V kicking up due to lightning transient, or the 5V or the control lines etc.?

author: PCB.Wiz
author_rank: Super Contributor
timestamp: July 28, 2025, 09:21:31 pm
content: Quote from: RustyShackleford on July 28, 2025, 05:39:01 pmHow much current is needed per dropper point ?Quote from: RustyShackleford on July 28, 2025, 05:39:01 pm'imagine' is into real Hail Mary territoryWith not much headroom, you may be better using high power zeners, which have more precise specs on knee turnover.Series impedance helps, but load current can limit series R scope

author: RustyShackleford
author_rank: Regular Contributor
timestamp: July 28, 2025, 10:38:26 pm
content: Quote from: PCB.Wiz on July 28, 2025, 09:21:31 pmNot quite sure what you mean by dropper point. There are a number of strings of LEDs, each driven. by a current-configured LT3081. The maximum current I allow is 360ma, which of course goes througheveryLED.QuoteHaha yes. Can't remember some ESD-related site where I read that absolute maximums for very brief events can be higher, but are rarely explicitly characterized. And tend to be governed by junction temperature limits.QuoteLooking at these zeners you mention. I'm looking at the 1N53 series, rated at only 5 watts (the highest power dissipation that Mouser shows for zeners), and I believe these curves (see attachment below) do indeed show the sharp knees.I can't afford any series R, because cuts into how many LEDs in series. But maybe some series inductance, placed in between the zener and a TVS ?

author: RustyShackleford
author_rank: Regular Contributor
timestamp: July 28, 2025, 10:44:15 pm
content: Quote from: floobydust on July 28, 2025, 08:15:45 pmSearch me. Wish I knew. When I connect to the USB port, the Arduino IDE doesn't see it. Didn't investigate further than that, except to note the onboard 3.3v regulator was not producing output and getting very hot. So I assume it's the 5v. The Arduino never sees the 30v at all. The 5v comes from a DC-to-DC converter driven from a 12vdc switcher that's there to support "legacy" (12v) landscape fixtures.