Eddy Current
Senior Member
I know salt can lower the resistance of water but is there a way to check waters resistance. Just wondering, and do they even make such a meter?
Can you check the resistance of water
- Thread starter Eddy Current
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GeorgeB
ElectroHydraulics engineer (retired)
- Location
- Greenville SC
- Occupation
- Retired
The reciprocal (conductance) is used more often with water. There are "conductivity cells" available at reasonable prices ... they have a known area of a conductive and inert (often platinum) metal spaced a known distance apart. Look up conductivity sensor on eBay ...
Pure water is an excellent insulator. Electrical generator stators (utility size) are often (always?) hollow and have very very very low conductivity water running through them as a coolant ... remember that we're talking 15kV to 40kV type voltages.
In the ignorance of youth, we made "arc lights" by making a resistor from salt water in a jar and nails through a piece of wood ... carbons from "D" cells ... and could control current by the amount of salt in the water. I wasn't but 10 or 12 years old, and didn't worry about electrocution <sad grin>.
Pure water is an excellent insulator. Electrical generator stators (utility size) are often (always?) hollow and have very very very low conductivity water running through them as a coolant ... remember that we're talking 15kV to 40kV type voltages.
In the ignorance of youth, we made "arc lights" by making a resistor from salt water in a jar and nails through a piece of wood ... carbons from "D" cells ... and could control current by the amount of salt in the water. I wasn't but 10 or 12 years old, and didn't worry about electrocution <sad grin>.
Eddy Current
Senior Member
I'm not getting why putting the apparatus he demonstrated in a bathtub full of water would cause the person in the bathtub to be electrocuted.
Why would the solution of salt in the water make a person IN the water be more likely to be electrocuted?
- :dunce:
Why would the solution of salt in the water make a person IN the water be more likely to be electrocuted?
- :dunce::dunce:
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
did not watch video. Pure distilled water does not conduct. Pollutants such as salt do.
Eddy Current
Senior Member
It looks like im guessing it would make you apart of the source of electricity and complete the circuit, turning on the bulb.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
The apparatus would not necessarily electrocute someone nor even shock them unless certain conditions exist. Take a fiberglass bathtub that has plastic drains, plastic water pipes. Now stick 120V in the water. If you get close to it you may get shocked but if you are one end you may not feel a thing. Salt changes things drastically.
Now a salted tub with you at one end and a 120V feed as shown in the demo may have some current flow thru the water and back to the bulb thru you but again if it is away from you I am not sure you will feel it. Put a metal grounded drain and now the current travels through the water and into the drain to complete the circuit.
If you did an experiment and took a lamp cord- no ground and connected it to a porcelain keyless socket, put in a wp flood bulb and dropped it in a plastic bucket of water. Will the GFCI trip? No.... If you stuck your hand in the water and you weren't grounded it would not trip the gfci. In fact you wouldn't even feel it unless you get close to the terminals. Add salt and I won't guarantee you won't feel it.
I'm not sure quite how to express this, and I'm certain that I don't want to try any of this, but why would this "bathtub water" not be somewhat comparable to an EGC.
I thought the whole purpose of that was to give fault current ( or in this case the light bulb jigger current ) a much better path to ground than YOUR path to ground.
As I am aware, the current takes all paths of resistance which could include the bather, but seems to me that adding salt would make the bather's resistance a much higher ratio to the total resistance than without the salt in the water.
Additionally, because of the additional volume and the current taking all paths, would the light bulb be more likely to light up in a large body of water than the beaker?
I thought the whole purpose of that was to give fault current ( or in this case the light bulb jigger current ) a much better path to ground than YOUR path to ground.
As I am aware, the current takes all paths of resistance which could include the bather, but seems to me that adding salt would make the bather's resistance a much higher ratio to the total resistance than without the salt in the water.
Additionally, because of the additional volume and the current taking all paths, would the light bulb be more likely to light up in a large body of water than the beaker?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Where is the fault if the water is not conductive? There is no fault to ground. I did this experiment- the bulb will stay lit under the water with a perfectly good GFCI attached to it. Inspectors would not believe it so I did a demo for them-- please don't do this unless you know what you are doing.
ptonsparky
Tom
- Occupation
- EC - retired
Making mistakes is what gives you experience, but don't let "He experienced life to the fullest." be heard to soon.
I think I did not express myself too well.
In the beaker water experiment, I see that there IS no fault current...and it would not trip a GFCI.... however the video guy said a bather in a bathtub would be more likely to be electrocuted with the addition of salt to the bath water... seems to me just the opposite.
in a bath tub there would be fault current, wouldn't there.... other wise what does the bather have to fear from decreasing the resistance of the bathwater by adding salt
It seems to me there are two resistances (impedances) of interest ... that of the bathtub water, and that of the bather.
The bather's resistance would stay the same, but the water's resistance would decrease with the addition of .salt.... so the proportional resistance of the bather in comparison to the total, should increase as the bathtub water's resistance decreases, shouldn't it? ... making him a path for less current instead of more.
I tried to compare that to an EGC ...which provides for a much better path for current flow than your body.... sparing your body from most of the current flow in a fault.
Maybe my whole point is just kinda dumb. I seem to be good at that.:huh:
In the beaker water experiment, I see that there IS no fault current...and it would not trip a GFCI.... however the video guy said a bather in a bathtub would be more likely to be electrocuted with the addition of salt to the bath water... seems to me just the opposite.
in a bath tub there would be fault current, wouldn't there.... other wise what does the bather have to fear from decreasing the resistance of the bathwater by adding salt
It seems to me there are two resistances (impedances) of interest ... that of the bathtub water, and that of the bather.
The bather's resistance would stay the same, but the water's resistance would decrease with the addition of .salt.... so the proportional resistance of the bather in comparison to the total, should increase as the bathtub water's resistance decreases, shouldn't it? ... making him a path for less current instead of more.
I tried to compare that to an EGC ...which provides for a much better path for current flow than your body.... sparing your body from most of the current flow in a fault.
Maybe my whole point is just kinda dumb. I seem to be good at that.:huh:
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Thank you for this post.
I had mentioned without a response in another post, how my brother in laws 200 amp panel was completely submersed (by a river) in his basement 3 times.........no short, no explosion, everything still worked (including the sump pump). This helped explain why and how.........................Thanks again.
I had mentioned without a response in another post, how my brother in laws 200 amp panel was completely submersed (by a river) in his basement 3 times.........no short, no explosion, everything still worked (including the sump pump). This helped explain why and how.........................Thanks again.
K8MHZ
Senior Member
- Occupation
- Electrician
You are correct. In fact, I don't think there has ever been a documented case of a person getting electrocuted in salt water, but that can't be said about fresh water.
http://www.huffingtonpost.com/terry-gardner/esd-hidden-danger-in-fres_b_693454.html
Fresh water is not pure water. It has ions in it like salt water, but far from the same amount. Fresh water has enough ions in it to conduct electricity but few enough so that the voltage gradients can be lethal.
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Little off topic but an experiment and a question if it could kill you.
Take a 12 or 24v bell transformer and a 9 v battery.
Hook the 9v battery to the low voltage side of the transformer and have someone hold the high voltage end..........they won't at first so you have to show them by holding it.
The fun part is, you then remove the battery connection causing the field to collapse sending the 9v dc into the transformer...........ouch.
I've tried this with my five kids all holding hands...........they all got it.
On a rough wired house (everything was dead) I had the GC hold the wires coming out of a receptacle telling him I needed to test something. I went to the other end of the house with my trusty 9v and bell transformer.....he got it.
Think someone could die horse-playing with this set up?
Take a 12 or 24v bell transformer and a 9 v battery.
Hook the 9v battery to the low voltage side of the transformer and have someone hold the high voltage end..........they won't at first so you have to show them by holding it.
The fun part is, you then remove the battery connection causing the field to collapse sending the 9v dc into the transformer...........ouch.
I've tried this with my five kids all holding hands...........they all got it.
On a rough wired house (everything was dead) I had the GC hold the wires coming out of a receptacle telling him I needed to test something. I went to the other end of the house with my trusty 9v and bell transformer.....he got it.
Think someone could die horse-playing with this set up?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I think the point of the example is this. Stick a probe as he did in the water while someone is in the tub in distilled water and it is very unlikely you can get shocked if you were touching a grounded water pipe while you are in the tub. Now add salt and the voltage will flow through the salt water thru you to ground. Again this is not a neutral and a hot conductor but a hot conductor and a switch leg. Sure most of the voltage will travel to the bulb but it will also take all paths.
When I did the experiment with tap water I finally shorted out the GFCI when I put the tester probe in a grounded outlet and the other lead close to the source. I still had voltage a foot away but not enough ma leakage to trip the gfci thru the water. When I got a few inches away with the lead is when it tripped.
When I did the experiment with tap water I finally shorted out the GFCI when I put the tester probe in a grounded outlet and the other lead close to the source. I still had voltage a foot away but not enough ma leakage to trip the gfci thru the water. When I got a few inches away with the lead is when it tripped.
K8MHZ
Senior Member
- Occupation
- Electrician
From what I understand it's more common for the source to be an on board 120 volt generator, but power to lifts, etc., can also pose a danger.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I totally understand the dangers in fresh water but remember fresh water is full of contaminates which would or could conduct. I don't see how salt water would not do the same.
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