Re: Current loops...

> +130vDC was often wired to places it wasn't desired, like to
> some conductors in a brand new VOICE cable in a central office,
> where an installer was terminating said cable on a dist. frame.,
> pliers on the wire, one hand on the ironwork. Nasty shock.
> But we won't go there..... / mark

Sure is a fast way to cure people of the "dental wirestripper"
habit!

I assume these were supply lines to the drivers - the whole point of
current loop is that the current source would only put out 60 (20) ma
on the data lines so the high voltage would only be there to draw upon
in overcomming resistance and inductance. Kinda like a modern stepper
driver (except that stepper drivers using switching "chopper" current
regulators, and these signalling current sources were probably
linear).

Oops, come to think of it 60ma can kill, and 20 ma would be a heck of
a shock. So the fact that it is current limited is not an issue - the
current delivered would be determined by 130v across your skin
resistance, with the current regulator unlikley to achieve its goal
before it runs out of voltage. Guess one wants to avoid the signal
lines too!

Chris

--
Christopher C. Stratton, stratton@...
Engineer, Instrument Maker & Horn Player
(978)538-5179 work, (617)492-3358 home
30 Griswold Street Cambridge, MA 02138
http://www.mdc.net/~stratton