Schrödinger's Kitten

Irreverent Science for Everyone

Monday 22 September 2008

Ways to Electrocute Yourself Around the Home

  • macro
  • safety
  • electrickery

I had a very bourgeois accident last week — while gaily opening a bottle of bubbly, fully half the bottle cascaded all over the gas hob, leaving me distraught and the hob sparking continuously for the next hour or so. In my wisdom, I decided to disassemble the hob, for ease of drying, using for protection the tea towel I used to sop up the wine. Who can tell me why this is a bad idea?

Yes, I got an electric shock. While cloth doesn’t conduct, wine bloody well does, being mostly water and all. When well-meaning parents tell their little darlings ‘electricity and water don’t mix’ (which is entirely content-free and unhelpful, except in the unlikely circumstance that they were using ‘don’t mix’ in some new slang context that means ‘the one conducts the other like an electrocuted mo-fo with a baton, Tourette’s and a symphony orchestra hanging on his every spasm’) they are setting them up for an incident such as this.

Of course, since I’m a highly educated kitten, I know very well that water conducts electricity — but since I’ve been to University, I also know that pure, distilled H2O doesn’t. Water molecules contain as many positively charged particles (protons) as negatively charged particles (electrons) and so completely ignore electric fields, in the same way that non-magnetic things aren’t bothered by magnetic fields. However, untreated water has impurities in it (that’s why you pay more for mineral water — it conducts!) and molecules of these impurities can have a net charge, so they do move when they experience an electric field. And when charged things move under an electric field, that’s a current. Distracted by this knowledge, and my grieving for the wine, I electrocuted myself.

Near-death experiences

So how close did I come to become Kentucky Fried Kitten? The ignition runs off mains voltage (240V en Angleterre). In order to spark, a difference in charge needs to build up on each side of the air gap, enough so that the atoms of air in the gap are torn apart into a positively charged nucleus and free electrons, so current can then travel across (a gas like this where not even atoms are held together is called a plasma. Plasmas conduct. Incidentally, fire is a plasma, so electricity will run through a circuit if you light a match in the gaps). But when the current has travelled across the gap, the charge across both sides has evened out, and the charge has to build up again. When you insert a kitten into the gap, two questions apply: a) how easy is it for current to travel through kittens? And b) what effect does this have on the kitten in question?

Well, kittens, humans and living things in general are 70% water, so 70% conductive, at least. The exact numerical value depends on how soggy the kitten is, which, since it had just had an impromptu sparkling wine shower, in this case is Very. So let’s say the kitten has a resistance of 1000 Ohms. (Resistance is the opposite of conductivity, how hard it is for current to get through. A dry kitten has a resistance of about 100,000 Ohms, for comparison.)

Will electrocution make me fat?

Voltage isn’t inherently damaging to living tissue. Birds are happy on overhead live wires, and electric eels (which aren’t actually eels, apparently, they’re knifefish, and they breathe air) can unleash 500V without any detrimental effects to themselves. The problem comes when there’s a different voltage on either side of you, which will cause a stabilising current to flow through you till the voltages are even. And since a fair amount of physiological processes rely on small, controlled bioelectric currents (nerves, brain cells, heart pulsation) a large whammy of extra current going through is A Bad Idea. Not to mention all the burny stuff and eye melty that starts to happen if the current continues.

This chart shows the effects of a given amount of current. We can use Ohm’s law Voltage = current x resistance to find the current through the kitten. The voltage is 240V from the mains, and assuming the four hob igniters are wired up in parallel, that’s what they each pump out... 240/1,000 = 240mA. “Venticular fibrillations1, fatal if continued”. Ouch. Or, if they’re wired up in series, each one only gets 60V. 60/1,000 = 60mA. “Beginning of sustained muscular contraction — can’t let go current.” That’s definitely more what it felt like.

So it was OK, just about. But still a bad idea. Anyway, this is the correct procedure for messing with live circuits, which I later adopted:

Don’t do it, kids. OK?


On the subject of other ways I like to take my life in my paws, I used to gaily push knives into toasters, reasoning that if they were live, putting my hands straight into current wouldn’t be any better than sticking a knife in and channelling the current through me indirectly. Furthermore, I reasoned, if the filaments had stopped glowing it was because there was no more current flowing through, so there was no current to flow through my arms in the first place.

And this is totally correct, if your toaster is put together properly and not damaged. If you had an incompetent electrician in the third world (or Wigan) wire it up, or if you’ve damaged it previously (say, by sticking a knife in it), this no longer follows. The knife-damage option is particularly worrying, since most toasters use mica (a non-conducting, brittle mineral) to separate the hot elements and keep them in the right place. And mica does not stand up well to knife attacks — much like the rest of us.

In the vast majority of cases, your toaster will be safe. But 17 Americans are electrocuted every year by their faithful kitchen bread-incinerators, and personally, if I’m going to put my life on the line, I want more out of it than some singed wheat products.

Aren’t there any stupid but fun things I can do with electricity around the house?

Why yes, kitten fans, you are completely fine to play electric guitar in the shower, swimming pool, sink or other accessible body of water (IMPORTANT CAVEAT: only safe if you have passive pickups, and if amp is correctly wired. Do not take amp in with you either, no matter how lonely it looks on the poolside2). I discovered this at a party when my friend Dikko decided to play said instrument in said body of water. Dikko knew that this was not dangerous — I was just drunk enough to think it was fun. It all ended happily, however, because of the way guitars work. Here's how the musical magic happens:

  • Guitar strings are made of magnetizable wire
  • Under them are pickups, little magnets wrapped in miles more wire (well, a mile)
  • As you pluck the string, it moves over the pickup, and the magnetic field in the pickup changes
  • Wires in changing magnetic fields get currents flowing through them
  • The wires wrapped round the pickups get current flowing through them
  • And now, a plucked string has been transformed into a varying electric current!

Transduction! Yay!3

Then the electrical signal goes to the amplifier, gets, um, amplified, and then runs through more wire and magnets to make speakers go in and out, pumping out heavy duty rock n roll. (Almost makes you want to get an acoustic for ease of explanation. Almost.)

Now let’s immerse this guitar. We’ve got current flowing through metal parts, surrounded by water. You are also in the water. Surely this is a problem? Relax — there’s really not a lot of current. On average, about 460 nanoAmps, actually — which is less than a thousandth of the smallest current humans can sense. The worst thing you have to worry about is the sound quality, which does, admittedly, suck. But if you want to be a real rockstar, you'll have to learn not to let things like that bother you.

1. Heart spasms — fun!

2. Kitten accepts no responsibility for argh argh burning sparks if these warnings are not followed. She has seen this done safely, so it is possible. But above caveats about it being safe only if correctly wired apply, along with above aspersions on the electrical skills of Wiganites. However possible things are in theory, there's always a risk. And this is where thinking for yourself and assessing probability helps. As a rule of thumb, if you play the lottery, get someone else to check over the odds for you.

3. For my next trick, a rabbit being removed from a black hole!

Content: Scary Boots — Design: Canis Lupus