[time-nuts] Line Voltage - USA
phk at phk.freebsd.dk
Mon Jan 2 12:55:58 EST 2017
In message <586A8B40.4050806 at erols.com>, Chuck Harris writes:
>Back in the dark ages of ~220V electrical distribution systems in
>Europe, the reaping due to unintentional grounding of a ~220V wire
>was so common and extreme, whole house ground fault interrupters
>were mandated for all residential/small business power systems
Close, but no cigar.
The main problem was that in many countries outlets did not have a
protective ground terminal.
That meant that an internal fault in your appliance had a 50/50
chance of lighting up some exterior metal part you could touch.
The "obvious solution" isn't obvious in countries where the geography
does not allow you to obtain proper "protective ground". Norway being a
But even countries with the "obvious solution" of protective ground
in all outlets saw problems, because it took 10-16 ampere misdirected
current to blow the fuse, and you can light most flameable stuff
with a lot less energy than that.
The "Residual Current Device" solved both problems.
RCD's even protect you from internal faults where proper protective
ground is not available, by providing neutral from "outside" the
RCD as PG in the installation. You'll still be (horribly!) exposed
of an accident in the distribution grid (or lightning!) fires up
the neutral, but that's simply life - or death - without a grounding
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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