Why wasn't I electrocuted?

onejontwo

Strange question I know but recently I carried out my weekly clean of my 125 litre aquarium, all was going well until I plugged the heater, pump, lighting and air stone back in. Everything worked apart from the pump. Now those of you that don't know, the pump sits submersed in the water with about 1 inch of lead submersed as well. I then stupidly put my hand in the water to shake the pump as this has cured it in the past as the pump is around 10 years old, but this didn't work so I pulled the pump out of the water only to find out what I initially thought was steam coming from the top of the pump, only to find it was smoke coming from a split live wire where it goes into the pump due to hardening of the outer brown case due to age. I quickly turned the power off. Then on closer examination I found a split of about a 5 mm on the copper wire
which caused the fault. Now on reflection the open copper wire was live in the aquarium when I put my hand in so my question is :- Why wasn't I electrocuted?

Rockingit

Assuming that what you are describing is a split in the insulation on the incoming 230V side which was submerged in the same tank of water as part of you, then the answer is simply extremely good luck in that some part of the system was insulating you from making a circuit - at a guess the soles on your shoes.

Had you had an RCD fitted in the system then it would (or, being picky, should have) tripped a long time before your fingers were anywhere near the water.

HOWEVER...... whilst knowing nothing at all about aquarium kit, I'd expect all the pumps etc to be SELV, which means that they have an external transformer and run from 12V or thereabouts.

onejontwo

I was in a pair of flip flops and the pump is only small with no transformer which plugs straight into the mains.

muckybutt

Rockingit wrote: »

HOWEVER...... whilst knowing nothing at all about aquarium kit, I'd expect all the pumps etc to be SELV, which means that they have an external transformer and run from 12V or thereabouts.

Most aquarium and pond pumps for that matter are 240 double isolated, even the heaters and air pumps are 240

spacey2012

Never question death, nor glory in it's forgiveness.
It does have ears.

Rockingit

onejontwo wrote: »

I was in a pair of flip flops and the pump is only small with no transformer which plugs straight into the mains.

may well have just saved your life.

May I suggest that you invest a tenner or so in a plugtop RCD (such as you use for lawn mowers) and run all your pump gear via it?

Or looked at another way, you just made yourself the ultimate MSE hero by saving around £4k on a funeral.

Rockingit

muckybutt wrote: »

Most aquarium and pond pumps for that matter are 240 double isolated, even the heaters and air pumps are 240

Which amounts to diddly squat if it's the insulation that has split!

Ben84

Rockingit wrote: »

May I suggest that you invest a tenner or so in a plugtop RCD (such as you use for lawn mowers) and run all your pump gear via it?

I was going to suggest this too. I never actually liked the idea of plugging something straight in the mains and sticking it in a tank full of water, in fact I'm surprised they're still made. Anyway, I'd probably spend a little more and replace the entire socket nearest the tank with an RCD socket, which will provide protection to any other items you're using in or near the tank. The potential electrical hazard from having a large volume of water in the room spreads out to a lot of appliances. You may for example have a TV set nearby, or an electric fire.

Rockingit

Ben84 wrote: »

I was going to suggest this too. I never actually liked the idea of plugging something straight in the mains and sticking it in a tank full of water, in fact I'm surprised they're still made. Anyway, I'd probably spend a little more and replace the entire socket nearest the tank with an RCD socket, which will provide protection to any other items you're using in or near the tank. The potential electrical hazard from having a large volume of water in the room spreads out to a lot of appliances. You may for example have a TV set nearby, or an electric fire.

Yep, that's good advice. Best practice would be to install whole-house RCD protection by (probably) investing in a consumer unit change, but not everyone can afford to get that done.

scheming_gypsy

If it was live then i'm guessing you'd have spotted a load of dead fish first.

Rockingit

scheming_gypsy wrote: »

If it was live then i'm guessing you'd have spotted a load of dead fish first.

Nope! The fish are effectively completely insulated. Even if there was 10,000V dropped into the tank, so long as the water stays within the glass (which is a superb insulator) there is no circuit to be made. It's what is known as the Faraday Cage principle. Have a look around on you tube for video's of people servicing ultra high tension power lines and radio masts whilst still live and you'll get the idea.