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From: jfa0522@hertz.njit.edu (john f andrews ece)
Newsgroups: sci.electronics,sci.geo.meteorology,misc.consumers.house
Subject: Re: using the bathroom during lightning storm
Message-ID: <1991May25.182850.19238@njitgw.njit.edu>
Date: 25 May 91 18:28:50 GMT
References: <1524@cvbnetPrime.COM> <1991May24.210108.9982@solbourne.com> <13568@dog.ee.lbl.gov>
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In article <13568@dog.ee.lbl.gov> jtchew@csa2.lbl.gov writes:
>>Correct me if I'm wrong here, but isn't the metal plumbing in your
>>house grounded?  
>
>In theory, yes.  The cold-water system is often regarded as one of
>the best grounds in the house.  
>
>However, gotta watch the broad statements. The drain/waste/vent  
>plumbing, which includes the waste stack below the toilet and the vent 
>pipe above it, is trending towards ABS, a rugged plastic, in many areas.  
>Also, metal D/W/V pipes are often joined by rubber connectors.
>
>The cold water supply might also include plastic (PVC) links, so the 
>only grounding there, at some points, would be by virtue of the water's 
>conductivity.  
>
>Various systems are often mixed by do-it-yourselfers or even contractors
>without caring about electrical matters.  Significantly, my cold and
>hot water pipes and gas pipe were bonded together (at the water heater)
>at the behest of the electrical inspector (who regarded the D/W/V pipes
>as a don't-care), not of the plumbing inspector.
>
>So here's a scenario: the best lightning target on a roof might well 
>be a piece of metal D/W/V pipe going down to a toilet, but thereafter
>grounded only by a spark + water path through the toilet and into the
>cold-water system.  And/or other good grounds nearby.  A weenie roast,
>so to speak, seems improbable but plausible.
>
>Remember that at a few tens of kiloamperes, fractional-ohm differences
>get really significant.
>
>--Joe
>"Just another personal opinion from the People's Republic of Berkeley"


I suspect it is more likely that only the drainage conduits may be PVC, as it
is still (last I heard) not considered safe enough for the drinking supply.

That would mean that as you stand, barefoot, on the ceramic tile floor,
making glorious contact with the water basin, you may be at risk. Of 
course, what are you doing barefoot on a grounded floor anyway???

(Can anyone quantitatively compare impedance of rest-of-water-in-pipes
to appendage impedance? That's the ticket ;-)