Today is the Old New Year, 12th January 2020.  The weather has been very unsettled the last few days, and we knew it would be wild last night. But what we weren't expecting was a period of prolonged thunderstorms.

The first crash of thunder woke me from a deep sleep, and at first I couldn't quite place what had woken me. But a few seconds later the flash in the room, visible through half-closed eyelids, followed almost immediately by a crash of thunder left no doubt that there was thunder and lightning about.  It was about 3.00am.  I decided to get up to disconnect the broadband router, as we have had several burnt out by thunderstorms in the past, just one by-product of ancient and not very well buried telephone cables in our area. More on telephone issues later. When I got downstairs, everything was in darkness and it took a second to understand that everything was in darkness, that the power was indeed off.

This is a rare occurrence for us, as our off-grid power supply is remarkably robust, power outages being usually planned to do some work on the system.  I knew there were a number of things that might be wrong, and all assumed disastrous proportions in my sleep-deprived mind. I was also aware that we had just re-stocked the freezer this last week, and Helen was happy that it was so full.  If we couldn't restore power, we stood to lose a lot of food.  I went to the kitchen to check on the instruments showing the incoming power from the wind charger and the power being used. There was plenty coming in, and the battery bank voltage was nicely high, but there was nothing being used, as expected.  I dressed to go out to the battery shed, as it now seemed likely that the main inverter, which turns 24v DC form the battery bank into 230v AC for use in the house, had been blown by the lightning. I was relieved that the wind charger, which sits on top of a 7 metre high pole, had not acted as a lightning conductor and was still working perfectly. 

The snow was swirling as I walked around the side of the house, and just before I got to the battery shed a bright flash of lightning turned the whole house and garden to day, followed well within a second by a crash of thunder - it was not the time to be outdoors.

In the battery shed, the inverter was showing its little "OK" green LED. It seemed fine. I pressed the buttons on the RCD earth leakage units that ensure we're unlikely to get severe shocks should an appliance misbehave, but nothing came on. On a whim, based on my old computer troubleshooting techniques of making a known change, then trying to understand the outcome of the change, if any, I plugged the light in the battery shed into the other RCD unit. The light came on. Curious.

At this time. I was trying to remember how I had installed the inverter, 11 years before. I knew I had two outputs from it, each feeding an RCD unit, with the power then going to the house or to Helen's dyeshed, and a separately controlled circuit for the battery shed, on a just-in-case basis.  I came to the conclusion that one of the AC outputs must be affected, but was relieved that the other appeared to be working.  A quick change of plugs, and the power to the house was restored. I was thankful, and unsure how to leave things, in case something bad was going on inside the inverter, but all seemed fine, so I thought I'd come back to it in the light of day.

I got back inside with a dry mouth and adrenalin coursing through my body. I had some water and settled back into bed, reading until the adrenalin subsided and I got back to sleep just after 4.00am.  No sooner had I dropped off than a huge thunderclap went off. It wasn't quite as bad as the occasion in the 1970s when the house we lived in in Malawi was struck directly by lightning, sparks flying off the metal windows and all, but it was still like being inside the speaker turned up to the the notorious 11. I tried the light hopefully but wasn't surprised that it did not come on.  I was now afraid that I really did not understand what was going on, so I switched off the inverter, hopefully leaving things in a safe state, and went back to bed, knowing there was little I could do until daylight.

Daylight came, and, on switching on the inverter, the opposite of what had happened during the night was the case - the other RCD unit, the one that didn't work in the small hours, now worked. I was quite stumped. So I took the cover plate off the inverter to see if there was anything obvious, like a blackening from a component blowing, although I was not expecting anything user-serviceable to be visible.  All looked fine.  It was at that point that I remembered that I had wired in two AC outputs, and that the inverter actually only had one output. So the problem must be with the RCD units.  This came as a pleasant surprise, as it means that the inverter was probably OK. To save being confused, I removed the one set of wires, and will make do with just the one set of RCD connections. But what could the problem have been?

Meanwhile, back in the house, we discovered the that transformer for the TV recorder box had blown.  I found a spare, and that came back up without problems.  A while later, we noticed that the lights on the DECT phone were out. Again, the transformer plug had no power output, but this time, when I found a close-ish match to try an alternate power source, the base unit itself was blown.  By the afternoon, we were hearing reports of both telephone and Internet services being out across Assynt. In fact, we are in the minority in having a working internet connection, perhaps because the power was down at the time the worst occurred. Our telephone exchange is truly ancient, and is one of the last handful of exchanges across the whole of the UK on the old "twentieth century network", as BT/Openreach calls it. A lot of the cabling is simply shoved into a shallow trench, rather than being deeply buried. BT/Openreach obviously doesn't believe in investing for yokels like us. In fact, a few months back, things were so bad that they had actually dismantled the management platform for these old exchanges, meaning our ISP had no way of managing our connection. It was only through the intervention of our MP that BT/Openreach magically "found" a management system to which they gave our ISP access.  So it is not surprise that lightning affected this system badly.

Other than those things, all seems to be well and operating normally in the house, in spite if the drama of the night.

Some speculation:  But those two blown transformers made me wonder. The manual for the inverter clearly explains that the inverter must be earthed.  It goes on to explain that neutral and earth are bonded, so that the RCD units, if something goes wrong, will trip and perhaps save your life.  But in the event of a lightning strike nearby, electricity will surge through the sodden sand that constitutes our soil in Assynt. That will be picked up by the earth rod. We already know earth is bonded to neutral, so there will inevitably be a difference between live and neutral. Now, to  electricians and physicists this may seem obvious, or it's wide of the mark. (do email me if you have any theories). But I think that difference tripped the RCD units, exactly as they should have done. Perhaps I did not hold in the reset button long enough or with enough conviction, or maybe they needed some time before being able to be reset.  But I now think all the protections actually worked as they should have done, although little would protect the precarious devices like cheap transformers or, of course, the phone lines.