Re: What does isolation actually mean?


"Abstract Dissonance" <Abstract.Dissonance.hotmail.com> wrote in message
news:11sa55r8q016c32@xxxxxxxxxxxxxxxxxxxxx
> Just about every time I see the word transformer I see the work
"electrical
> isolation" but I really have no idea what it means. Obviously there
are is
> no direct electrical connection but whats the big deal with this? Why
is it
> important to isolate the mains, say, with an isolation transformer
when it
> decreases efficiency?
>
> I just don't see the point of isolating something just to isolate it..
there
> has to be a very good reason but no one seems to mention it. Like one
could
> use AC to power a motor that powers another motor that generates AC
and
> hence there is an electrical isolation... but what good is it?

Primarily, it stops you from getting electrocuted by ensuring that there
is no DC path for current. Take TVs for example. Being the cheapest
possible design, they rarely if ever include a transformer. Typically,
the chassis is connected directly to one side of the AC (it's called a
"hot chassis" so you can google it). Since they usually only have a
two-prong plug, there's a good chance that the chassis could be
connected to the "hot" side of the AC line. Let's say, being the
curious sort that you are, that you decide to take your new scope and
examine some of the signals on the circuit board. You boldly grab the
ground connection to the scope and clip it to the metal chassis in
preparation for probing. After the sparks and blinding flash of light
subside and you hopefully are still breathing, you then fully understand
what a "hot chassis" is and then go out and promptly buy yourself an
isolation transformer to use on the next TV that you decide to poke
inside. ;-)

Another place that I can think of needing an isolation transformer is
when trying to hook a scope to a phone line. The ground at your house
is not quite the same potential as the ground connection at the CO. On
top of that the CO uses a negative power supply (meaning that their 48V
batteries have the positive terminals connected to ground) something
like the system that very old motor vehicles used.


.

Relevant Pages

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