24 Nov
2014
24 Nov
'14
6:03 p.m.
On 24/11/2014 08:52, Brent Hilpert wrote:
Well, I'm willing to entertain counter-intuitive
notions but I'm
really not convinced. Some reading suggests going beyond the current
level at which one loses intentional muscle control, while it will or
can result in involuntary muscle contractions, those contractions may
be more likely to result in hanging on rather than getting kicked
off, and you're more likely to exceed that current level with the
higher voltage. Getting 'thrown off' also has it's own set of
associated risks.
I was just reporting what I read, which came from one of the members of
the committee that made the decisions - after much "discussion",
apparently. To be honest, I doubt there's much difference, and
certainly any voltage in those regions can be fatal. In fact, much
lower voltages can be fatal, if applied to broken skin such that current
passes across (actually, through) your chest. That's why there's such a
category as SELV. Yet I remember once getting a very painful shock from
a 9V PP3 battery when a couple of terminals went through my skin, but
fortunately only across one hand.
But isn't there an internal logic problem in there
to begin with? I
thought the point of the step-down/isolation transformer for portable
tools was to reduce the 240V to a safer level (or is just to make it
easier for manufacturers, to only have to manufacture 110/120V tools
worldwide?
Not really, the point is to reduce the maximum to *50V* above ground,
which is below the 90V (?) "safe" threshold.
in which case one would think the onus would be on NA to
change). Those transformers aren't required in NA
because we're only
operating at 120V. Once you require the transformers to get down from
240V, you might as well go to the center-tapped 55-0-55 technique at
a small increase in complexity over 0-110 for a further safety
improvement.
As the EU requires.
--
Pete