On Fri, 2006-12-08 at 00:32 +0000, Tony Duell wrote:
[For those who wonder what on earth I am talking
about, portable
industrial power tools -- electric drills, for example -- in the UK are
110V devices. They're run off a step-down isolating transformer, the
secondary of which is centre-tapped with the tap connected to ground. The
idea is that if the insulation fails, or you cut through the cable, or,
then the maximu voltage you'll get if you touch one bit of metal is 55V
(one half of the transformer output, returning to ground through you).
This voltage is unlikely to prove fatal.]
Interestingly, that is how U.S. Navy power on-board ships works,
too. (Well, as of 25 years ago... *SIGH*) Two out-of-phase 60 volt
live sides. U.S. standard house wiring is, however, three wire: Live,
Neutral, and Ground at 120 volts, 60 Hz. Some equipment we used on the
ship was designed for land-based labs, and case-grounded, which meant
that when you plugged them in, you were shorting out half the mains.
Yikes. We had isolation transformers for THAT equipment which were
ungrounded. Installing new equipment was even more exciting there than
most places. <Grin>
Peace,
Warren E. Wolfe
wizard at
voyager.net