Who's rewired their house for this hobby?
hilpert at cs.ubc.ca
Mon Nov 24 02:52:27 CST 2014
On 2014-Nov-23, at 5:46 PM, Pete Turnbull wrote:
> On 23/11/2014 22:12, Brent Hilpert wrote:
>> The benefit of the North American split-phase system vs EU/Britain is
>> you have the energy & copper-efficiency of 240V available for heavy
>> appliances, but you have the safety factor throughout the house of
>> never having more than 120V between you and earth.
> That's not as much of a safety factor as many people think, indeed possibly not at all. It's true that 230V will give you more of a jolt than 120V, and more so because human body resistance drops slightly at higher voltages. Nevertheless, there's a strong argument that a 230V jolt is more likely to throw you off the conductor whereas 120V may be more likely to make you latch onto it. It depends how you touch it, obviously, but evidence suggests that (EHT excepted) the region around 100V-130V is about the most dangerous. I recall reading a discussion of that as part of the European harmonisation of voltages, in connection with 110V for site equipment. Evidently that was in part why the idea of one live and one neutral with a single simple MCB or RCD was rejected in favour of the split 55-0-55 system (proposed by the UK).
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.
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?, 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.
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