Resistance of water

[gman2003]

Just curious. What is the resistance of water? I had a discussion recently with someone about GFCI's and their purpose in protecting against shock hazards near water sources, and was just wondering what the resistance was. Thanks.

[ June 08, 2003, 09:45 PM: Message edited by: gman2003 ]

 

[roger]

Re: Resistance of water

For the sake of conversation, water itself is non conductive. What we have to take into consideration is the salts and metals in water as we know and use it, which takes it to a conductive source that can range from high to low resistivity.

Roger

 

[gman2003]

Re: Resistance of water

Hey Roger,

The conversation came about when someone with a fish aquarium recieved a slight shock when he stuck his hand into the water while cleaning it. The pump inside the tank had begun shorting out but did not trip the breaker. The water just stayed energized until he found out which pump it was and then he removed it. He is now putting his equipment on a GFCI receptacle, but I was just curious about the properties of water when it comes into contact with electricity as far as it's resistance being too high to clear a fault. It is a freshwater tank, so I assume since the salinity is very low, then the resistance will be very high?

[ June 08, 2003, 10:09 PM: Message edited by: gman2003 ]

 

[dereckbc]

Re: Resistance of water

Its all about the mineral content of the water. Salt is just one of the minerals.

 

[wayne123]

Re: Resistance of water

The conductivity varies depending on what part of the country you live in ie: coastal plains water has high salinity. If you live in an area such as that I would suggest trying water that has been processed through a water softner which helps eliminate high quanities of calcium an magneseum.

 

[gman2003]

Re: Resistance of water

So then, in this particular freshwater aquarium setup that has a low salt/mineral content (except for what may be added by the water treatment plant), if one of the electrical components short and current comes into contact directly with the water, then the shock will not be as severe as it would for a saltwater tank, or where the salt/mineral content of the water is high? And even if the mineral content is high, it would not be high enough to trip the circuit breaker, would it? Sorry for the elementary questions, but I'm just trying to understand the property of water as it relates to electric fault current. Thanks.

 

[karl riley]

Re: Resistance of water

Another factor involved in GFIs near sinks: does not the water present on the sink decrease the resistance between skin and sink? Is this a function of the water's conductivity or a kind of spreading out of the skin contact area?

I would like to solve this by experiment but I don't like the tingling sensation.
Karl

 

[charlie b]

Re: Resistance of water

does not the water present on the sink decrease the resistance between skin and sink?

It does. It?s the same concept that comes into play when a person who has been working (i.e., sweating) is more susceptible to electric shock. Damp skin has a lower resistance than dry skin. For that matter, damp dirt has a lower resistance than dry sand, and that accounts for different ground resistances in different parts of the country.

Is this a function of the water's conductivity or a kind of spreading out of the skin contact area?[/QB]

Both.

 

[eprice]

Re: Resistance of water

Is the aquarium properly grounded? What is the path for the fault current back to it's source (when the person is not present)? It doesn't matter what the resistance of the water is if there is no low impedance path from it back to the power source. It will just set there energized until someone or something completes the circuit.

 

[racraft]

Re: Resistance of water

Most home aquariums are not grounded, and in fact cannot be grounded. They are all glass with plastix trim. There are no metal parts. Salt water aquariums cannot have any metal parts, because of the salt and the rusting issue.

As for the equipment, most home aquarium pumps, filters, heaters and lights are simple two wire cord and plug. There is no equipment ground.

 

[eprice]

Re: Resistance of water

Originally posted by racraft:
Most home aquariums are not grounded, and in fact cannot be grounded. They are all glass with plastix trim. There are no metal parts. Salt water aquariums cannot have any metal parts, because of the salt and the rusting issue.

As for the equipment, most home aquarium pumps, filters, heaters and lights are simple two wire cord and plug. There is no equipment ground.

That pretty much confirms what I was thinking, so the way I'm seeing it, regardless of the resistance of the water, if a motor developes a fault to the water, there is no path for the fault current to follow until someone sticks their hand in

 

[don_resqcapt19]

Re: Resistance of water

What else is the human touching to create a path for current to flow, or is the current only flowing across the skin that is in the water? The wet skin having a lower resistance than the water itself and acting in parallel with the water.
Don

 

[gman2003]

Re: Resistance of water

He wasn't touching anything else, he only felt a slight shock when cleaning the tank. He found out that it was a powerhead, which is a submersable pump that has it's electrical components sealed in epoxy. But evidently the epoxy seal gave way somewhere. Yes, most all filters, pumps, heaters, etc... are only two prong plugs. So with this current in the water, if by chance had he been touching something else that was grounded, he might have felt more than a slight shock.

 

[brian john]

Re: Resistance of water

And then remember the fish have a bad habit of defecating in the water, high mineral content in that I'm sure. As for the ground, could be the carpet, depending on the age of the aquarium the light fixture older fixtures were metal, newer one are plastic).

Could be wrong, but I would think the current was most likely flowing only with the human interface, seems if the current was present for any period of time the fish might be belly up.

 

[pierre]

Re: Resistance of water

In order for current to flow, there has to be a complete circuit. As was said, the pumps are doublely insulated, so there is no path to ground for fault current and when the person stuck his hand in the tank, somehow completed the circuit. Without knowing more about it is hard to say why.

Pierre

 

[wocolt]

Re: Resistance of water

What is the resistance of water?

From what I remember from chemistry 111 water with a ph of 7 is neutral and will not conduct electricity, ie either side of 7 it will conduct up to 14 is basic and to 0 is acidic.
The skin is not a perfect insulator and wet skin is even less impervious to electricity. Once inside the body electricity finds a good conductor, the blood and other waters which are made up primarily salt which really enhances conductivity.
I am sure somebody has a web-site which has studies, done on the conductivity/resistivity of skin.

WmColt