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"Gail" <gail (at) sql in the wild (dot) co [dot] za> wrote:
> I've seen similar happen in an old flat I was renting at University. Don't
> know how it happened (not an electrician), but something in the geyser
> shorted and left all of the hot water pipes (and the water) live.
> It's times like that when having a friend who's father works for the city
> council as an electricial comes in handy.
Wow. Reminds me of a short from The Three Stooges :)
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Stephen wrote:
> Tom Austin <taustin> wrote:
>> Stephen wrote:
>>
>>> Here are a couple of tips for everyone when working on live equipment. Wear
>>> insulating footwear and keep one hand in your pocket. That way the current is
>>> less likely to find a path through your body.
>>>
>> I am not an electrician, so I know enough to be dangerous.
>> Actually, I studied electrical engineering - so I know enough to keep
>> mostly safe.
>>
>> I was thinking I would write about keeping a hand in the pocket, but you
>> beat me to it.
>>
>> I always have a hand in my pocket when routing wires in my main electric
>> panel where I can't easily turn everything off. It isn't enough to just
>> keep a hand away - by instinct you will use it to grab on to something.
>>
>>
>>
> I get nervous working over 5V Vcc.
I've been scared of that as well - especially when the circuit that I
wired up actually blows things up. I got so jumpy at one point I had to
have someone else hook it up to smoke test it.
>>
>>
> A mere tingle :P
> 240 V is not too bad it hurts more but is bearable if it is just through your
> hand. And most of the shock is just shock people do get used to it and can even
> deliberately touch live connectors to test the voltage. The trick is to do it
> fast and the pain level will tell you the voltage. The same way that I learned
> to see how close to boiling water is by dipping my fingers into it (FAST). The
> human body is very resilient.
>
>
Never thought of it like that, but it makes sense.
The problem is that someone without experience tries to do it and gets
themselves hut.
Tom
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scott wrote:
>> Some non-electricians will hook up the earth as a common - using it as
>> the return path for the hot.
>>
>> In this case the potential will vary with the amount of current on the
>> wire.
>
> But I think that Buildings Standards require that the resistance to
> ground be low enough that for the Earth voltage to become dangerous,
> enough current must flow to blow a fuse. Otherwise this kind of
> relatively common fault would leave metal cases of everything in the
> house electrified to dangerous voltages!
>
When a layman looks in an electric panel he sees that the bare copper
ground and the white neutral (U.S. colors here) attach to the same point
they start to think they can use the bare copper as the neutral.
While it isn't terribly shocking, it does cause a voltage on what is
supposed to be grounded.
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Gail wrote:
> Don't know how it happened (not an electrician), but something in the
> geyser shorted and left all of the hot water pipes (and the water) live.
I was working at a place once where we were doing CP/M development, back
before LANs and stuff. So we had the serial ports on all the machines
hooked to long wires that came up to what could only be called a patch
panel (for connecting machines together, and machines to modems).
One day, "Hey, I can't get the Apple ][ to talk to the Kay-pro."
"Try the Vernace."
"Nope."
"See if the Vernace will talk to the Kay-pro."
"Nope."
"Try the Radio Shack."
"That doesn't work either."
After a few such tries, one of us got a tingle trying to plug the serial
connector into the patch panel. Oh, jeez, house current on the serial
port ground. We managed to fry every single serial port, except that the
radio shack machine had 2 and we only fried one of them.
--
Darren New / San Diego, CA, USA (PST)
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On Wed, 15 Oct 2008 10:34:11 -0700, Darren New <dne### [at] san rrcom> wrote:
>
>After a few such tries, one of us got a tingle trying to plug the serial
>connector into the patch panel. Oh, jeez, house current on the serial
>port ground. We managed to fry every single serial port, except that the
>radio shack machine had 2 and we only fried one of them.
>
You're bringing back memories ;)
That reminds me of a job years ago (about 1975). I was using a scope to check
the current flowing through a component and had disconnected the mains earth
wire so that the scope was floating. {So that the probe's reference ground would
not be connected to earth and short out the component's power supply (before
double insulated or floating return paths on scopes. A valve job IIRC)} Every
time someone touched the scope they got a tingle. Looking into it I found that
when the scope's mains filter had been put on back to front and there was a
capacitive bridge between the live-earth-neutral making the chassis sit at 120
Volts. It was limited current but a really sharp tingling.
--
Regards
Stephen
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On Wed, 15 Oct 2008 12:39:19 -0400, Tom Austin <taustin> wrote:
>
>I've been scared of that as well - especially when the circuit that I
>wired up actually blows things up. I got so jumpy at one point I had to
>have someone else hook it up to smoke test it.
>
Nothing wrong with that IMO ;)
>>>
>>>
>> A mere tingle :P
>> 240 V is not too bad it hurts more but is bearable if it is just through your
>> hand. And most of the shock is just shock people do get used to it and can even
>> deliberately touch live connectors to test the voltage. The trick is to do it
>> fast and the pain level will tell you the voltage. The same way that I learned
>> to see how close to boiling water is by dipping my fingers into it (FAST). The
>> human body is very resilient.
>>
>>
>
>Never thought of it like that, but it makes sense.
>The problem is that someone without experience tries to do it and gets
>themselves hut.
Yes, you don't do it in front of children. The boiling water thing was shown to
me by someone in the catering trade. There are a couple of tricks for snapping
un-insulated wire you can do. One involves putting a kink in the wire that
fatigues it and makes it break before it cuts you and another that spreads the
pressure over your knuckle stopping it from digging in.
Send $10 and a SAE for the secrets :)
--
Regards
Stephen
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Darren New wrote:
>
> One day, "Hey, I can't get the Apple ][ to talk to the Kay-pro."
>
That brings back memories, BTW. One of the first computers I actually
had my hands on was a Kaypro. I remember thinking CP/M was very similar
to DOS, later I learned DOS was based on CP/M.
> After a few such tries, one of us got a tingle trying to plug the serial
> connector into the patch panel. Oh, jeez, house current on the serial
> port ground. We managed to fry every single serial port, except that the
> radio shack machine had 2 and we only fried one of them.
>
Ouch. How did that happen, BTW?
--
~Mike
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Mike Raiford wrote:
> That brings back memories, BTW. One of the first computers I actually
> had my hands on was a Kaypro. I remember thinking CP/M was very similar
> to DOS, later I learned DOS was based on CP/M.
Yep. Same system calls and everything. You were supposed to be able to
re-assemble your assembly code for CP/M and have it Just Work on the
IBM-PC. It really wasn't *just* the Microsoft deal that made it work.
> Ouch. How did that happen, BTW?
Dunno. Something inside one of the machines touched something it
shouldn't. It probably started with the Apple, which got opened up more
than the other machines.
--
Darren New / San Diego, CA, USA (PST)
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