This week, I received a ~240V AC electric shock. I can’t recommend it.
We’re currently having our attic converted, so we’ve had some electricians in doing the necessary electrical wiring. Shortly after they first arrived they discovered that our existing electrics were pretty catastrophic, and needed to make a few changes including a new fusebox and disconnecting the hilariously-unsafe distribution board in the garage.
After connecting everything new up they began switching everything back on and testing the circuits… and we were surprised to hear arcing sounds and see all the lights flickering.
The electricians switched everything off and started switching breakers back on one at a time to try to identify the source of the fault, reasonably assuming that something was shorting somewhere, but no matter what combination of switches were enabled there always seemed to be some kind of problem.
Noticing that the oven’s clock wasn’t just blinking 00:00 (as it would after a power cut) but repeatedly resetting itself to 00:00, I pointed this out to the electricians as an indicator that the problem was occurring on their current permutation of switches, which was strange because it was completely different to the permutation that had originally exhibited flickering lights.
I reached over to point at the oven, and the tip of my finger touched the metal of its case…
Blam! I felt a jolt through my hand and up my arm and uncontrollably leapt backwards across the room, convulsing as I fell to the floor. I gestured to the cooker and shouted something about it being live, and the electricians switched off its circuit and came running with those clever EM-field sensor pens they use.
Somehow the case of the cooker was energised despite being isolated at the fusebox? How could that be?
I missed the next bits of the diagnosis of our electrical system because I was busy getting my own diagnosis: it turns out that if you get a mains electric shock – even if you’re conscious and mobile – the NHS really want you to go to A&E.
At my suggestion, Ruth delivered me to the Minor Injuries unit at our nearest hospital (I figured that what I had wasn’t that serious, and the local hospital generally has shorter wait times!)… who took one look at me and told me that I ought to be at the emergency department of the bigger hospital over the way.
Off at the “right” hospital I got another round of ECG tests, some blood tests (which can apparently be used to diagnose muscular damage: who knew?), and all the regular observations of pulse and blood pressure and whatnot that you might expect.
And then, because let’s face it I was probably in better condition than most folks being dropped off at A&E, I was left to chill in a short stay ward while the doctors waited for test results to come through.
Meanwhile, back at home our electricians had called-in SSEN, who look after the grid in our area. It turns out that the problem wasn’t directly related to our electrical work at all but had occurred one or two pylons “upstream” from our house. A fault on the network had, from the sounds of things, resulted in “live” being sent down not only the live wire but up the earth wire too.
That’s why appliances in the house were energised even with their circuit breakers switched-off: they were connected to an earth that was doing pretty-much the opposite of what an earth should: discharging into the house!
It seems an inconceivable coincidence to me that a network fault might happen to occur during the downtime during which we happened to have electricians working, so I find myself wondering if perhaps the network fault had occurred some time ago but only become apparent/dangerous as a result of changes to our household configuration.
I’m no expert, but I sketched a diagram showing how such a thing might happen (click to embiggen). I’ll stress that I don’t know for certain what went wrong: I’m just basing this on what I’ve been told my SSEN plus a little speculation:
By the time I was home from the hospital the following day, our driveway was overflowing with the vehicles of grid engineers to the point of partially blocking the main street outside (which at least helped ensure that people obeyed our new 20mph limit for a change).
Two and a half days later, I’m back at work and mostly recovered. I’ve still got some discomfort in my left hand, especially if I try to grip anything tightly, but I’m definitely moving in the right direction.
It’s actually more-annoying how much my chest itches from having various patches of hair shaved-off to make it possible to hook up ECG electrodes!
Anyway, the short of it is that I recommend against getting zapped by the grid. If it had given me superpowers it might have been a different story, but I guess it just gave me sore muscles and a house with a dozen non-working sockets.
In the picture, I think you’re very wrong about one thing. I think that deer knows EXACTLY what’s going on.
10/10 diagram. I appreciate the inclusion of the oblivious local wildlife
I think it’s surprising that you would believe the… “problem wasn’t directly related to our electrical work at all but had occurred one or two pylons “upstream”” …because the electrician who electrocuted told you so, I mean he’d probably tell you it was static to avoid blame.
17th edition electrics is pretty Mickey Mouse. Basically, your guy went and messed up because he didn’t understand the wiring and came up with a bullshit excuse.
Thank goodness that it was only you that got some sore nipples from this!
So on the specific mechanism of the fault, I don’t think it was preexisting (particularly since the steadily increasing light flicker through Monday wasn’t otherwise apparent until a few hours before the Incident.
Instead, after speaking to a ridiculous number of electricians, my understanding of the problem is that it wasn’t (technically) that the Earth became Live, but that a clamp which ensures our feed from the high power lines had corroded enough to short.
This made the Neutral live.
At this time, the house was earthed using PME, or Protective Multiple Earthing. In PME, the system is grounded by multiple earthing points *on the Neutral line*. Normally this is very good because it means the path to Earth is really short…
…except the shorting clamp gave us a ‘floating neutral’: because there was current on the Neutral, we not only effectively lost Earth, but also everything Earthed became live (but at less than 100v, presumably, since the main fuse didn’t blow). In this sense the Earth did become live, but because of the PME system rather than the fault itself.
As far as I can tell, the old Earth over at the garage wouldn’t have helped even if it was connected, because at the house end, our Neutral / Earth had lost all grounding anyway (so the path that should have grounded any fault was already compromised). (Also, not actually sure if the supply cable to the garage was connected to the old generator Earth in the absence of the generator? It might not have linked in anyway!)
But anyway, we now have 3 clamps instead of 1, and they’re new instead of knackered, and also we no longer have PME, we’re now using TT Earthing with a big Magic Stick as a grounding rod. So hopefully we can’t have it happen again! 😅
Also, this week was the first time I wished I’d paid more attention in Year 9 Physics.
TIL!
scary!
yikes, glad you’re ok! Electricity is wild.
Also, you’ve got a very small typo in one of your captions. It reads “confirming that yet, he really had”, where it should say “yes, he really had”
Thanks, typo corrected!