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If the power is still on in a house that is flooded and someone walks in the water, why/how are they not electrocuted?

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1469 utenti della rete avevano questa curiosità: Spiegami If the power is still on in a house that is flooded and someone walks in the water, why/how are they not electrocuted?

I keep seeing videos of people coming home to a burst pipe or the neighbors above them having a flood. The water pours down from the ceiling and from the light fixtures (lights are on), but the people walking around the house don't get electrocuted.

Ed ecco le risposte:

Water isn’t nearly as good a conductor as movies and TV makes it seem, it also doesn’t just “electrify all the water” and then zap you for touching it like you might see in media.

In short electricity won’t just “fill the water”, electricity wants to go somewhere. So for example if you have a flooded room with something like a high-voltage wire in it, that electricity will either want to stay in the wire, or leave the wire and flow somewhere, like into a near by metal sewer pipe that can send the electricity to the ground. In this case the electricity would be traveling through the water like lighting through the air. Just because there is lightning outside, it’s like being outside in the air just fries you instantly, you need to get hit by the lighting. And that’s why walking around in a field or touching metal objects during a storm can be dangerous, because the lighting can decide it does want to travel through you.

IT IS STILL DANGEROUS though because if you enter the water you can become that path for the electricity (like standing outside on a flat field holding a metal rod during a thunderstorm). For example if you enter the water and then you touch the metal sewer pipe now you’re part of the path from wire to water to sewer pipe and that’s muy no bueno for you.

In the videos you see people are either desperate or idiots. You absolutely should not end water that has the potential of being electrified.

I saw videos about electrical safety in my electronics manufacturing class during college

where people absolutely do wade into potentially electrified water and then get shocked, fall into the water, and/or die.

There were several examples in the videos we watched.
There was a flooded basement with an electric water heater, there was a rainy driveway with a metal ladder and a light fixture, and a few more. Didn’t know I was going to watch people die on camera in class that day, whoops.

Stopping or recovering from the situation is tough because it can be difficult to isolate the power or to de-energize the area, so it may be impossible to stop the situation or to recover or save the person affected without becoming a victim yourself. You really can’t see whether it’s safe to enter the water or not in the first place.

The other commenters are right in that there are plenty of reasons that it probably won’t hurt you, it might have tripped a failsafe, or it could maybe be diffused enough to not have a noticable effect.

But those are all just rolling the dice. No guarantees.

It’s not something you can always see; so call a professional, or get help. It’s one of those things that you could be right and you could fine most of the time, maybe; but on the off chance that you’re wrong, you could be dead.

In order for current to flow it needs to be able to flow from somewhere to another place. All wires in your house are made up of two electrical conductors, one live and one neutral. This means that in an appliance current can flow from live and back to the neutral conductor. In case of failures it is possible for the current to flow from live to ground, possibly by using a human as a conductor. This is what could hurt you.

If your house is flooded then current can flow through the water. In general it takes the least path of resistance which is the shortest path. But because the wires and contacts include both the live and neutral wire, and often a separate ground wire, the shortest path of resistance is usually just over to the neutral or ground wire. Even if someone is standing next to the outlet the neutral wire is much closer and therefore most of the current flows there.

But even if you somehow had a situation where only the live conductor was in touch with the water then water is a very poor electrical conductor. It is much better then air but still very poor. Human flesh is actually a much better electrical conductor which is why the current goes through flesh rather then through the water. But the relatively low voltages you find in most homes have a very hard time going through the water at all. Even with the added salts from muddy water in the case of a flood which improves the electrical conductivity of the water it is unlikely to see shortcuts through much water. The standard household outlets even have the contacts far enough apart so they will not short between them even in water. The danger actually comes from the wires behind the outlet and the inside of switches and such. So you would have to be almost holding the live wire under water to get electrocuted.

And lastly modern building codes require that special RCD devices be fitted which cuts power to any circuit that have a fault before there is enough current to kill people through the fault. So even if you get a shock the power gets cut before it does any permanent damage. This is of course assuming your buildings electrical systems are up to code.

Enjoy this guy showcasing the precise danger of water and electricity:

The rate at which voltage drops off in water is incredibly fast. Your home has 240 volts maximum. Even in conductive water it at most could travel maybe a foot. Even a lightning strike is dissipated within about 5 feet of where it strikes (otherwise you would have lakes full of dead fish every thunderstorm).