3 phase residential with one leg 'out' - Page 11

 from david.williams@bayman.org (David Williams) contains these words:


  

 The british 13 amp plug (typically referred to as "Plugtop" - don't
ask, I don't know either! ;-) have a small cartridge fuse fitted. This
is only accessable when the appliance is unplugged. It can be fused with
either a 1, 2, 3, 5, 7[1], 10 or 13 amp fuse.

 The fuse rating is supposed to be determined by the cord's amperage
rating. Sometimes this alone will suffice to protect the appliance as
well (typically kettles, toasters and so on), but low power devices will
have their own, suitably rated, fuse protection, leaving the 1 or 2 or 3
amp fuse to protect the appliance cord.

 Since this is an essential part of the safety feature in this system
intended to guard against non -routine events on an indivual appliance,
a cheap and cost effective fuse is all that is required. A mini cb in a
plugtop is simply an unnecessary 'luxury'. Hell! even circuit breakers
on the consumer unit are totally overkill. I've been living in this
property for just over 25 years now and never had a (re-wirable yet!)
fuse bridge blow.

 That 13 amp plugtop limit limits the maximum KVA rating to 3 for a
nominal 240vac supply. I have one such appliance, an electric kettle
(which doubles up quite nicely as a 2.5KW test load on the 221vac from
my recently purchased PowerCraft 2.8KVA max (2.5KVA continuous) rated
petrol (gasoline) backup generator).

 Unfortunately, even after reducing the rpms on the governor [2] to
bring the frequency down to 52Hz on no load (49Hz full load) from its
original 53.5Hz, I'm still having problems with my venerable APC
Smart-UPS 2000I despite setting the dip switch to desensitise it to poor
quality supply. Apparently, it can be desentised even more through
software but I have yet to make up the interface cable to test this. If
I can't get this setup to work, I'll be returning it as unsafe
_as_well_as_ not fit for purpose since the tank fuel guage has a serious
leak which only shows up when fully fuelled and represents a serious
fire hazard (I'd already replaced the stepped rubber washer on the fuel
tap connection to the tank which had started leaking)

 Apparently (after a googling marathon) this is quite a common problem
whenever an UPS is involved. Not only is the excessive speed setting a
common issue (eg 64 Hz for an american generator - well outside of the
+/-5% limits for a UPS), but, after recording the generator waveform
using a quality 12vac output wallwart to isolate the laptop from the
mains, using a resistor network to reduce the 12vac down to half a volt
for the line input and analysing the frequency spectrum, I'm not
surprised!

 The output contains considerable harmonic content, the effect of which
is quite visible to the naked eye when expanding the display to show a
cycle or two. I thought the utility power's "approximation to a sine
wave" was bad enough, but that generator makes this look 'pure' by
comparison! I can't understand why they can make something so simple (a
sine wave) so bad.

 Incidently, the sinewave output from the APC Smart-UPS 2000I looks
purer than the utility supply's effort. I suspect the departure from
sinewave is most likely due to the load characteristics rather than the
utility's generators.

[1] The 7 amp fuse is not a commonly available one. The most common fuse
ratings being 3, 5 and 13 amp (with 13 amp being the most common).

[2] No help whatsoever from the manufacturer's website, just a closer
inspection of the throttle control linkage to see that this was
obviously determined by an adjustment screw.

--
Regards, John.

 Please remove the "ohggcyht" before replying.
The address has been munged to reject Spam-bots.