Assume that a house has public water and sewage.
It is plumbed entirely with plastic – supplies and drains, fiberglass tubs, molded plastic sinks. There are no GFCI’s.
You are sitting in a tub of water (30 gals), a 110v 15a max current is applied to the water.
Will you get a shock? will it be lethal? Does the water in the tub have enough mass to provide a ground?
the above scenario, except you take a shower instead of a bath. You reach out and contact a live 110v 15a max source of current.
I suspect that the shower water, which is connected to all the water in the city, will provide sifficient mass to provide a lethal ground. Agree/disagree?
Replies
Who you trying to get rid of? How big are they?
Might be you could get shocked, but might not. So if you like throw an electric cord in the tub and it doesn't work, you are so busted dude.
The water will conduct electricity, but a lot depends on the purity of the water. It might be possible that the damp "crud" in the drain pipes would be enough to complete a circuit in some cases, but, in other cases, if the water is pure enough the conductivity through the water pipes and shower head may not be enough to cause a problem.
Of course, if you toss a fairly large device (with both hot and neutral) such as a toaster into the tub, there may be enough of a "field" around the device to cause a lethal shock, even without another ground (and without the person touching the device). A lot depends on the configuration of fields in the water, and how the person is positioned in them.
Having said all that, GFCI outlets are cheap enough there's no real reason to not have one in a bath area, and even in adjacent areas where one might be tempted to plug in an extension cord to power a boombox or whatever next to the tub.
Curiously, though, the GCFIs will do a slightly better job of protecting folks if the tub is grounded somehow.
As others have said, pure water is a lousy conductor. It has only 10 to the -7 ions (H+ and OH- ) in it. That is 1 ion per 10,000,000 water molecules. Vinegar has 1,000,000 times more ions in it. The ocean has 1,000,000 times more ions in it.
If you live in NY or SF you have very pure mountain snow-melt water and can use it in batteries, contact lens, etc.
But most of the country has water with more TDS (total dissolved soilds) in it. Maybe 10 to 100 times more. 1000 times in parts of the mountain west. And if you do (or need to) soften the water, then you have a lot of ions in it: +1 ions and +2 ions, respectively.
Summary: you'd probably get a little buzz. Probably wouldn't kill you. Your mileage may vary. Do not try this at home.
Oh, and install those GFCIs, they're only $10 and one will probably cover the whole bathroom.
Thanks for all the serious (and not so serious) input. The way I worded the question may have lead some to think I was advocating eliminating GFCI's which is not the case - my wife was saved by one a couple of months ago. It just occured to me recently that this hazard may all be based on metal piping and I don't understand electricity well enough to answer the question myself.
I can't answer your question completely, but will throw in my two cents.
The size of the circuit is not really relevant, because 0.1 amps for 1 second is generally fatal. Any household circuit could supply 0.1 amps.
What's relevant is the resistance that will allow that much current to flow at 120 volts, and whether or not the length of water between the tub and ground has less than that amount. If the water has less than 1200 W resistance then you'll have a fatal level of current at 120 volts.
I don't have any books with the right data, but if one knew the conductivity of typical household water, which maybe you could get from a municipality, and assumed a pipe length, from that the resistance could be calculated.
"If the water has less than 1200 W resistance. . . .if one knew the conductivity. . . ."
The shallow GW I usually measure is between 30 and 2000 µS/cm (microsiemens per centimeter). Household water would often be in the range of 5 to 50 µS/cm.
GFCIs trip at what? 0.006 amps? And to stop breathing, 0.024 could do it (5000 ohms between 120 and ground).
So don't sweat it! Because dry skin is 20,000 ohms. But if you get nervous. . .
David Thomas Overlooking Cook Inlet in Kenai, Alaska
I think the net-net is that having plastic plumbing and fixtures will reduce but not eliminate the hazards associated with electric shock. And the amount of reduction (if GFCIs are installed and in good condition) from having plastic plumbing is probably not worth considering, except maybe in special situations (hospitals, etc). You're not being "careless" if you install metal vs plastic.
Actually I think that there are cases where plastic plumbing might be more damagerous.
GFCI only protect against ground faults, not where the fault is hot to neutral.
If the device is dumped in a tub and there is not enough ground fault current because plastic piping then the GFCI won't trip. But the person will be within the hot to neutral field and bye-bye.
Yep, that's why I said that grounding the tub would actually improve the protection provided by GFCIs.
(One exception, though, is things like hair driers with built-in GFCIs in the cord. As I understand it, these include a 3rd "ground" wire in the cord so that they can detect a device-in-the-water fault, even if the water is effectively ungrounded.)
You need to conduct some experiments. Please have an assistant to take notes, that way, she/he can report the findings even if you are not around to let us know what happened. ;-)
Why don't you try it and get back to us?