On Feb 24, 21:15, Eric Smith wrote:
> Hans wrote:
> > What's proper or not is a matter of opinion, and in my mind
> > open relays are a basic part of the mail system.
>
> Can you cite any legitimate use for a completely open relay? I can't
> think of any. Lacking such examples, I agree with Scott G. Taylor's
> statement:
> > The simple fact-of-the-matter is, open relays are wrong.
My ISP runs two SMTP mail servers, one open, the other not; for a very good
reason. A large number of customers travel across Europe, and it is not
practical for them to always dial the ISP at international rates. Hence,
there are a number of agreements between several ISPs in several European
countries, which allow customers registered with one ISP to use the
points-of-presence of another. However, the roaming user typically wants
to keep his normal email address (ie, have mail appear to originate from
his normal address). To do so, he must either use his "home" server
despite his temporary IP address/hostname not matching that server's domain
(which would look like an attempted forgery to a spam-blocking server) or
must use the "local" server and forge the sender address (which would also
fail on any normal spam-blocking server).
This practice is quite widespread in Europe. Jay's use of MAPS doesn't
bother me, because I can (almost) always use the blocking server, and I
expect that for most roaming users the inconvenience is minimal. However,
until there's a sensible system to deal with roaming users' need to send
mail as well as receive it, there will be open relays.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York
The ringing voltage is over 250 volts peak-to-peak but at a high enough
voltage to make you jerk your hand away if you touch it. The voltage range
that's most dangerous is from 25volts to about 60 volts, as it won't make
you jerk your hand (or other body part) away, yet it is capable of
disrupting normal operation of the cardio-vascular system.
I've never seen a precise write-up of what it takes to kill you, but I'd
avoid contact with voltages such as this just to avoid the pain.
Dick
-----Original Message-----
From: Bruce Lane <kyrrin(a)bluefeathertech.com>
To: classiccmp(a)classiccmp.org <classiccmp(a)classiccmp.org>
Date: Monday, February 28, 2000 8:25 AM
Subject: Re: Is ringing voltage dangerous?
>At 05:56 28-02-2000 -0800, you wrote:
>
>>You know, I've been told it's painful, but is it dangerous?
>
> <snarph>
>
> Any voltage along those lines can be dangerous if it passes through the
>chest. My understanding is that it takes less than 20mA of current flow to
>kill a person.
>
> Be safe rather than sorry.
>
>
>
>-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
>Bruce Lane, Owner and head honcho, Blue Feather Technologies
>http://www.bluefeathertech.com // E-mail: kyrrin(a)bluefeathertech.com
>Amateur Radio: WD6EOS since Dec. '77
>"Our science can only describe an object, event, or living thing in our
>own human terms. It cannot, in any way, define any of them..."
Careful, Joe . . . the ring voltage spec I remember said it was about 128
volts AC centered about the battery voltage, which is conventionally -48
volts. That's where the 80-volts at 20 hertz comes from, since that's what
you see by way of a rectifier diode. That's not a true sinusoid, though,
it's the humps from a sinusoid rectified to ground when the median of the
sinusoid is at -48Vdc.
I don't really know that this can kill or even harm you in some other major
way, but it's unpleasant enough that it makes sense to avoid it. That urge
to pull my hand out of the box when I'm bitten by a higher voltage than I
like is what's made me unwilling to work on TV sets with their puched
chassis, etc.
Dick
-----Original Message-----
From: Joe <rigdonj(a)intellistar.net>
To: classiccmp(a)classiccmp.org <classiccmp(a)classiccmp.org>
Date: Monday, February 28, 2000 9:45 AM
Subject: Re: Is ringing voltage dangerous?
>At 05:56 AM 2/28/00 -0800, Danial wrote:
>>You know, I've been told it's painful, but is it dangerous?
>>I just told another group about the supply I have (It outputs 110AC, 30hz,
>>.06 amp), and realized it's 110. Isn't that dangerous? If I really did
zap
>>my kid brother with it, would it just hurt or could it really HURT him?
>>-------
>>
>
> No, it'll just hurt him. It'll sure get his attention though! I've been
>shocked by them dozens of times. FWIW the normal (US) telephone ringing
>voltage is only 48 volts or so. The old telephones and military field
>phones with the hand cranks with put out over 100 volts. Those hurt!
>
> Joe
>
These comments are clearly made by someone who has experience with this
matter!
Dick
-----Original Message-----
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
To: classiccmp(a)classiccmp.org <classiccmp(a)classiccmp.org>
Date: Monday, February 28, 2000 4:40 PM
Subject: Re: Is ringing voltage dangerous?
>>
>>
>> >RULE 1, unless the voltage is very low it _can_ be dangerous. Low is
hard
>> > number be exact about but, over 12-30V is the watch out zone.
>> >RULE 2, All efforts are to be made to avoid crossing the heart or chest
>> > as a possible path for safety. One hand in pocket rule is
derived
>> > from this.
>> >RULE 3, if you not sure, make sure. get a meter and find out if it's
live
>> > and how hot hot is.
>>
>>
>> I just want to add a rule - Don't always trust what the meter says. I
took
>
>I believe that when working on live power lines and other circuits
>carrying dangerous voltages, you test the meter on a known HV source,
>then you test the line, then you test the meter again on said known HV
>source. Then, normally, you connect the power line to earth, assuming
>it's shown to be dead. And only then do you touch it.
>
>Some HV meters used for this sort of thing have a 'proving unit' (a small
>PSU that gives out a few kV at a minimal current, running off batteries)
>in the carrying case for these tests.
>
>> 1950 v from an electron multiplier supply because the meter read around
40
>> volts. There was a common failure mode of this supply that it would shut
>> down to 40 v. Instead of walking around to shut it off before
>
>Ouch!. That's not pleasant :-(. Oh, and never trust indicator lamps (they
>can burn out), and never trust on/off switches to isolate something. Pull
>the mains plug and put it where you can see it (or some idiot will plug
>it in again).
>
>I'll add another 'rule'... When you are sure something is not live, brush
>it with the back of your finger. If, by some strange chance it _is_ still
>live, your finger will be thrown off. Touch it with the front of your
>finger and you'll be forced into better contact with it.
>
>-tony
>
I didn't expect such a response for this! Tell you what I'll do, since I
don't really have the proper facilites for making good copies of the
extended pages...I'll just scan it and post it within the next couple of
days to the web site.
BTW, the actual nice paper copy I have was spoken for within 5 minutes or
so of my original post...
Cheers,
Aaron
>RULE 1, unless the voltage is very low it _can_ be dangerous. Low is hard
> number be exact about but, over 12-30V is the watch out zone.
>RULE 2, All efforts are to be made to avoid crossing the heart or chest
> as a possible path for safety. One hand in pocket rule is derived
> from this.
>RULE 3, if you not sure, make sure. get a meter and find out if it's live
> and how hot hot is.
I just want to add a rule - Don't always trust what the meter says. I took
1950 v from an electron multiplier supply because the meter read around 40
volts. There was a common failure mode of this supply that it would shut
down to 40 v. Instead of walking around to shut it off before
disconnecting the meter (after all the supply was dead right? ) I just
disconnected the meter. Surprise the supply was good and the meter was
dead. I almost was also. I had severe cramps in that arm and shoulder for
almost 2 days.
Dan
>Over the years working with RF and transmitters I've been hit with RF and
>DC to 1800V (ouch!) and LF AC power to 200V/400hz. Some were annoying,
>a few painful, one nearly bluecrossed me and the better ones left scars
>(and a willingness to NOT stick fingers in).
>
>
>Allison
>
>
Hi all,
I finally got the rest of the RT-11v2 System Reference Manual online
tonight:
http://www.prinsol.com/~aaron/classiccmp/rt11v2manual/
I haven't had time to put together the rest yet (appendices, etc.) and I
also have release notes from Fortran IV and some other stuff to put up.
Also in the works are a couple of handbooks and the like, an IBM
System/360 Fortran IV manual, some older SunOS docs...and whatever else I
can find around here to scan.
Cheers,
Aaron
:wq
No, I wasn't really gonna zap my kid brother! That was a hypothetical question.
I was more worried about zapping myself, and I try to follow the one-hand-in
your-pocket rule whenever I can. I know better than to zap anyone with anything
I wouldn't zap myself with.
(But a good shot of signal voltage (+28VDC, 2 amps) across his earlobes next
time he gets out of the shower is very tempting! J/K!)
Oh, and the 9V battery story, I got told it was a Navy guy who fell on his
voltmeter probes. It's probably another urban legend.
-------
You know, I've been told it's painful, but is it dangerous?
I just told another group about the supply I have (It outputs 110AC, 30hz,
.06 amp), and realized it's 110. Isn't that dangerous? If I really did zap
my kid brother with it, would it just hurt or could it really HURT him?
-------
