Re: Isolation transformer

On Sun, 06 May 2007 00:35:02 +0900, spamfree@xxxxxxxxxxx wrote:

But you haven't actually said HOW it helps, have you?
I'm trying to understand how an IT helps with grounded chassis
equipment and polarised three pin plugs to the mains. jack

It still helps if you touch the mains power wires or wires and parts
that aren't isolated from ground - while standing on damp concrete
with leather shoes or leaning on a grounded scope - both sides of the
line to the equipment being repaired are isolated from ground so you
could theoretically grab hold of the hot mains wire and still keep
breathing.

That's essentially what wikipedia and your other responders are
telling you.

Draw the circuit using a stick figure, ground his leg, have him touch
the hot incoming un isolated mains voltage. See the path from hand to
ground? Now put an isolation transformer in the circuit with the same
stick figure - no path to ground, and as long as he touches only one
conductor on the secondary side of the mains, he's breathing.

The reason they suggest keeping one hand in your pocket while working
around live circuits. You ain't lived till you've gotten across the
B+ of a tube transmitter - it will change your perspective on a lot of
things if you survive the first mistake.

One of the ironies is very high voltages MAY leave you alive. I
watched a navy tech open the door on a transmitter and he shut it
down, we all heard the safety relays slam down when he hit the
disconnect (just opening the door would have also done it) -
supposedly shorting the power supply, he then put the grounding stick
on the HV cap according to SOP - and drew an arc from his ass to the
scope cart where he was kneeling. He joked about it for about 5
minutes, then the reality hit him and he turned white and went into
shock, and pissed all over himself.

Polarized plugs grounded chassis and all are great things for safety -
you can add more safety if you want (and given that you are having
trouble with a relatively simple concept, perhaps you should - unless
you worship Darwin or something).

The +12 volt terminal on battery in a boat can be mighty
uncomfortable with salt water all over your hands, kneeling on a wet
deck - and a small cut you didn't know was there, will really bring
the idea home fast.
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