Floods and Electricity

finix

Why don't people get an electric shock when flood waters reach say a socket on the wall.? Does it trip immediately ? Just curious, Thanks.

Bruthal

finix wrote: »

Why don't people get an electric shock when flood waters reach say a socket on the wall.? Does it trip immediately ? Just curious, Thanks.

Contrary to the vast majority of people thinking water is a good conductor of electricity, its actually a very poor conductor.

Sockets may or may not trip quickly, depending on circumstances.

zega

It's the minerals in water that conduct electricity isn't it?

Bruthal

Pure distilled water is more like an insulator than a conductor. Normal non distilled water has impurities in it, and salts, providing ions in the water to allow it to conduct.

It is a poor conductor though, even though wet hands will provide a far better connection to live terminals when hands are in contact with them, than dry hands. This leads to the assumption that water is a good conductor. Anything more than a few centimeters and it will conduct very little, unless the contact area is very large compared to the distance conducted through the water.

brightspark

Don't forget that electricity will take the shortest path, (lazy ).

Most of the current will flow directly between the contacts in the socket, leaving a much smaller amount available further away.

Of course if you were to be closer to the outlet will might get a shock. Got one once from a wet extension lead, before rules about site safety were common.

Davy

They used to use distilled water in large circuit breakers unless im mistaken

Bruthal

brightspark wrote: »

Don't forget that electricity will take the shortest path, (lazy ).

Most of the current will flow directly between the contacts in the socket, leaving a much smaller amount available further away.

Of course if you were to be closer to the outlet will might get a shock. Got one once from a wet extension lead, before rules about site safety were common.

In reality, if electricity only Ever took shortest/easiest paths, nothing would work properly. You would want to be awful close to the socket to perceive anything. The overwhelming majority of the water surface area would be in contact with ground potential areas.

SpaceTime

Not to mention that flood water is usually full of minerals. In Cork City Centre it's even likely to be slightly salty.

I wouldn't be very confident that it's an insulator. It's more likely things are shorting to earth. There would be plenty of earth wiring, plumbing, metal objects etc

Mostly things you'd find the submerged wiring would short to neutral and/or earth causing everything to trip or fuses to blow.

I would still suggest isolating power before entering a flooded property.

finix

Bruthal wrote: »

Contrary to the vast majority of people thinking water is a good conductor of electricity, its actually a very poor conductor.

If its so poor why the big thing about not using electrical appliances in the bathroom, and why is the light switch always outside the bathroom ?

brightspark

finix wrote: »

If its so poor why the big thing about not using electrical appliances in the bathroom, and why is the light switch always outside the bathroom ?

Even though it is poor only a small amount of current is required to cause ventricular fibrillation, somewhere on the region of 100mA, (you get painful shock and loss of muscle control at less than half of that).

In the bathroom you are often wet and will form the shortest path to earth through your body (wet hands with bare wet feet on the floor!), this can easily allow sufficient current to flow to be fatal.

Wet hands on a standard light switch is never a good idea, not to mention that within the bathroom there is the possibility of high humidity making the switches wet too.

Unlike the submerged socket where (hopefully) the current flowing between the contacts should trip the RCD within 300ms, long before any significant current flows through your body.

SpaceTime

You'll also be standing in bare feet on tiles and near well earthed plumbing or even in direct contact with it which makes shocks even more possible.

The approach in most Continental European countries and in the USA is to use RCDs though and it seems to work just as well as our rather more old fashioned approach.

Some even require 10mA RCD protection.

We allow electric showers which are only IP rated as splash proof on the basis they're RCD protected.

finix

brightspark wrote: »

Even though it is poor only a small amount of current is required to cause ventricular fibrillation, somewhere on the region of 100mA, (you get painful shock and loss of muscle control at less than half of that).

In the bathroom you are often wet and will form the shortest path to earth through your body (wet hands with bare wet feet on the floor!), this can easily allow sufficient current to flow to be fatal.

Wet hands on a standard light switch is never a good idea, not to mention that within the bathroom there is the possibility of high humidity making the switches wet too.

Unlike the submerged socket where (hopefully) the current flowing between the contacts should trip the RCD within 300ms, long before any significant current flows through your body.

Excellent answer, even a layman could follow that ! I love plain English !

Bruthal

brightspark wrote: »

Wet hands on a standard light switch is never a good idea, not to mention that within the bathroom there is the possibility of high humidity making the switches wet too.

A person would want to be unlucky to get any sort of shock with wet hands on a switch all the same. I know some here will dispute that. But will that be based on what is assumed, or real life experience.

I know a fair few times on farms I got a few tingles while switching damp switches in outhouses with feet nice and damp as well. The average person on the street would jump in terror at such a tingle, believing they have been almost electrocuted, and just about regained their balance after been "thrown" across the room.

Fatal electric shocks just about always involve at least two good points of contact other than the feet, or else a fully live item in hand, and knee deep in cement or a similar situation.

brightspark

Bruthal wrote: »

A person would want to be unlucky to get any sort of shock with wet hands on a switch all the same. I know some here will dispute that. But will that be based on what is assumed, or real life experience.

I know a fair few times on farms I got a few tingles while switching damp switches in outhouses with feet nice and damp as well. The average person on the street would jump in terror at such a tingle, believing they have been almost electrocuted, and just about regained their balance after been "thrown" across the room.

Fatal electric shocks just about always involve at least two good points of contact other than the feet, or else a fully live item in hand, and knee deep in cement or a similar situation.

People often have wet bare feet on a wet floor as well as wet hands in a bathroom, that's probably why the switch is outside the bathroom.

Maybe your skin is thicker and more leathery than the average person on the street.

Bruthal

brightspark wrote: »

People often have wet bare feet on a wet floor as well as wet hands in a bathroom, that's probably why the switch is outside the bathroom.

Im talking about switches in general. But there would be more of a danger from switches in bathrooms from people slipping in terror at the slightest hint of a shock, than from shocks themselves.

Maybe your skin is thicker and more leathery than the average person on the street.

No, its just people expect an outcome based on perceptions rather than what actually does happen.

2011

Bruthal wrote: »

A person would want to be unlucky to get any sort of shock with wet hands on a switch all the same.

Indeed they would.

However it goes without saying that when enough people with wet hands touch enough switches enough times it is inevitable that someone will suffer a fatal/serious injury from electrocution.

That is why I would agree with this statement:

Wet hands on a standard light switch is never a good idea

tomdempsey200

i've received a few tingles from removing DZ fuses,13amp plugs and the like


must be sticky conducting stuff on them

i usually use gloves for fuses or the back end of a pliars for switches.. if i'm in doubt


i'm not too fond of getting a rattle

Bruthal

2011 wrote: »

Indeed they would.

However it goes without saying that when enough people with wet hands touch enough switches enough times it is inevitable that someone will suffer a fatal/serious injury from electrocution.:

A sliver of water in through the side of a rocker and onto terminals?

No realistic chance of fatal shock there without other major factors. There is a risk of secondary injuries more than electrical.

If enough people partake in any activity, someone dies sometime.

That is not to say I recommend wet hands and switches. I dont.

Even very mild tingles can cause injury through secondary impacts from panic etc.

2011

Bruthal wrote: »

No realistic chance of fatal shock there without other major factors.

It could be argued that no one individual has a realistic chance of winning the lottery, yet every few weeks someone does.

That said, I understand that the main thrust of your argument is that the chances of sustaining serious injuries or a fatality from an electric shock are quite remote.
I would imagine that in these rare cases there are other factors, such as the victim is suffering from a medical condition.

There is a risk of secondary injuries more than electrical.

Agreed.

That is not to say I recommend wet hands and switches. I dont.

Indeed.
I think we pretty much agree on this one.

SpaceTime

It's surprising that bathroom lighting never required RCD protection.
It's an obvious risky area and things like mirror lights are easily touched.

Is it required now?

French wiring is fully RCD protected these days. Usually they use multiple RCDs, each covering a row of circuits. All lighting is included but mixed across several RCDs so one trip won't leave a whole area in darkness.

2011

SpaceTime wrote: »

It's surprising that bathroom lighting never required RCD protection.

It does now.
My personal view is that this is OTT.

French wiring is fully RCD protected these days.

From what I have seen the standard of wiring of domestic installations in France varies considerably. Many homes there have no RCDs at all, some have a single RCD for the entire board (IΔn of 100mA), most have sockets in bathrooms, many socket outlets do not have an earth and earthling in general is often lacking / non-existent.

SpaceTime

2011 wrote: »

It does now.
My personal view is that this is OTT.



From what I have seen the standard of wiring of domestic installations in France varies considerably. Many homes there have no RCDs at all, some have a single RCD for the entire board (IΔn of 100mA), most have sockets in bathrooms, many socket outlets do not have an earth and earthling in general is often lacking / non-existent.

I mean modern French wiring. The rules have tightened enormously and new installations are actually pretty top notch.

A lot of older French installations were pretty dangerous. There also seems to be a lot more extremely old wiring still in use in France than here.

I stayed in an old hotel with pre WWII wiring & early 50s stuff still in use!!

You also get a lot of bad DIY work in French domestic installations.

2011

SpaceTime wrote: »

I mean modern French wiring. The rules have tightened enormously and new installations are actually pretty top notch.

You may be correct, I am not familiar with their regulations.

A lot of older French installations were pretty dangerous. There also seems to be a lot more extremely old wiring still in use in France than here.

Agreed.
I have also noticed that the Italians in general are not fans of earthing (but they tell me that they make up for it with their cooking ability).

tomdempsey200

SpaceTime wrote: »

It's surprising that bathroom lighting never required RCD protection.
It's an obvious risky area and things like mirror lights are easily touched.

Is it required now?

French wiring is fully RCD protected these days. Usually they use multiple RCDs, each covering a row of circuits. All lighting is included but mixed across several RCDs so one trip won't leave a whole area in darkness.

UK is pretty much all rcd now for domestic too

Its a general rule with rcds that you avoid creating a nuisance.. I think it's in the wiring rules somewhere

You would often see strip lights and bathroom lights with covers missing or damaged.. If I recall that was part of the reasoning behind the rcd for bathroom zones

SpaceTime

That's a typical modern French setup:

http://leniddecastors.free.fr/wp-content/uploads/Tableau-electrique.jpg

Inter. diff = RCD
Parafoudre = Lightening surge arrestor.
Chauffe-eau = hot water heating.

Bigger systems would typically be 3-phase.

There different types of RCD are used too A, AC and HCI.

Tuco88

As far as I am aware the UK's standard is very like the Irish one, Unless the C&G 17th edition has been changed since I last did it.

Will there be a day that everything will be on an RCBO in a domestic dwelling? Never mind the cost atm but for a practical view, given that there will probably always be an application where an RCD is not practical in a Com/Indus scale.

Regards Nuisance tripping for lighting, the lighting in one of the plants we carry out work in has all the lighting on RCBOs in a new area of the plant, this area is around 4 years old. Any time they tripped 8/10 times it meant there was a fault in a fitting of some sort.

Bruthal

Tuco88 wrote: »

Any time they tripped 8/10 times it meant there was a fault in a fitting of some sort.

The other 2/10 times might be someone breaking their neck falling in their dark bathroom. That would seem a higher risk than being electrocuted by the bathroom light.

Tuco88

Bruthal wrote: »

The other 2/10 times might be someone breaking their neck falling in their dark bathroom. That would seem a higher risk than being electrocuted by the bathroom light.

Bathroom light is already on an rcd... unless you have the luxury of a second zone. a new house usually will have greater number lighting circuits than 2. Any electrician can balance out the circuits as best he can, as was done is the factory case.

2011

Bruthal wrote: »

The other 2/10 times might be someone breaking their neck falling in their dark bathroom. That would seem a higher risk than being electrocuted by the bathroom light.

Agree, sometimes increased "safety" can make a situation more dangerous.

Bruthal

Tuco88 wrote: »

Bruthal wrote: »

The other 2/10 times might be someone breaking their neck falling in their dark bathroom. That would seem a higher risk than being electrocuted by the bathroom light.

Bathroom light is already on an rcd... unless you have the luxury of a second zone. a new house usually will have greater number lighting circuits than 2. Any electrician can balance out the circuits as best he can, as was done is the factory case.

That post doesnt really seem to have much connection to my one.

My point was, in reply to you saying 8/10 trips were due to identifiable problems, im saying that leaves 2 out of 10 nuisance trips, which in a bathroom, leaves a bath or shower user in darkness.

So to explain my point, its
A: Non RCD protected bathroom light
B: RCD protected bathroom light.

Neither is much of an electrocution risk. But B has a higher risk of leaving people in a slippy bathroom in darkness. B in my opinion has a higher risk of causing injury etc than A.

Sir Arthur Daley

Bruthal wrote: »

im saying that leaves 2 out of 10 nuisance trips, which in a bathroom, leaves a bath or shower user in darkness.

This is why I would recommend non slip tiles no more tripping.