Invisible <voi### [at] devnull> wrote:
> Stephen wrote:
>
> > I’ve seen them connected to plastic water pipes and a fat lot of good that would
> > do :)
>
> Isn't that illegal?
>

Yes and not very effective.


> > In new builds you will often find a metal rod driven into the ground as an
> > earthing electrode.
>
> "I think having a lightning conductor on a church represents an
> extrodinary lack of faith."

Is it not to protect the church from the devil ;)
A bit like a high tech gargoyle.

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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've been lucky, I've never been hit with anything more than 110v


Tom

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Warp wrote:
> Orchid XP v8 <voi### [at] devnull> wrote:
>> Nope. As the Wikipedia article explains, there are sprung-loaded plastic 
>> covers that only move out of the way as the earth pin is inserted.
> 
>   Is it guaranteed that the difference in potential between the earth pin
> and the physical ground is always very close to zero?
> 

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.

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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’m not an electrician either nor an electrical engineer but an electronic on so
I get nervous working over 5V Vcc.
That hasn’t stopped people asking me to work on power systems which was the
reason I stopped working offshore. It was getting too dangerous.

If you can’t put your hand in your pocket grab hold of the back of your
waistband.


> I've been lucky, I've never been hit with anything more than 110v
>
>
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.


Stephen

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> 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!

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> Yeah, some bathrooms have special "shaver" sockets which are weird 2-pin 
> connectors fused at 2A or something. Personally, I don't know about you, 
> but my bathroom is so tiny that you'd be just as well to go somewhere 
> else... ;-)

It appears that the forthcoming 17th editiion of the building regulations 
(aren't you excited!) in the UK will allow normal 13A sockets in a bathroom, 
if they are protected by a 30mA RCD and not too close to a shower/tap...

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scott wrote:

> It appears that the forthcoming 17th editiion of the building 
> regulations (aren't you excited!) in the UK will allow normal 13A 
> sockets in a bathroom, if they are protected by a 30mA RCD and not too 
> close to a shower/tap...

How in the name of God do you know that? o_O

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>> It appears that the forthcoming 17th editiion of the building regulations 
>> (aren't you excited!) in the UK will allow normal 13A sockets in a 
>> bathroom, if they are protected by a 30mA RCD and not too close to a 
>> shower/tap...
>
> How in the name of God do you know that? o_O

My mum asked me a while ago about putting a socket in her bathroom, so I 
looked into it then.  It appears that now you are actually allowed normal 
sockets in your bathroom (Wikipedia was a bit out of date).

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"scott" <sco### [at] scottcom> wrote in message news:48f4a20e@news.povray.org...
>> 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!
>

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.

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On Tue, 14 Oct 2008 07:38:36 +0100, Orchid XP v8 <voi### [at] devnull> wrote:

>Stephen wrote:
>
>> Incidentally when you see medics using that "Stand Clear, Stand Clear" electric
>> defibrillator. They are not starting the heart but stopping it. Think on :)
>
>It's like rebooting a computer. Gotta shut it down to make it start back 
>up again in normal working order. ;-)

True
-- 

Regards
     Stephen

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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’m not an electrician either nor an electrical engineer but an electronic on so
> 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] sanrrcom> 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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