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G3OYU > INFO 05.07.02 20:59l 60 Lines 2717 Bytes #999 (0) @ WW
BID : 0D0854G3OYU
Read: DB0FHN GUEST
Subj: Re: 110V - 230V and 13A Plugs.
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Sent: 020702/0830Z @:GB7ZZZ.#38.GBR.EU #:39647 [Ringmer] FBB7.00i $:0D0854G3OYU
From: G3OYU@GB7ZZZ.#38.GBR.EU
To : INFO@WW
EI3DIB wrote:-
> tests showed the optimum voltage to be around 200 but from a mathematical
> point of view it made more sense to use 250 as this then made the 3 phase
> voltage 500
Incorrect. 250V single phase gives 433 volts 3 phase. The conversion is
single phase voltage times the square root of 3.
>Most marine equipment is a maximum 110 Volt
Also not correct. The Royal Navy certainly use both DC and AC. I worked
on HMS Eagle, as a civilian, back in the 60s, she had nine 200V DC
generators and five 240V 50 Hz generators. She also had some 115V 400 Hz
generation capability, for servicing the aircraft, Buckaneer and Sea
Vixen.
The purpose of the fused plugtop does seem to be getting very confused.
The purpose of the fuse in the 13A type plugtops is solely to protect the
appliance mains cable AND NOTHING ELSE. Protection of the equipment
should be done within the equipment. Take a look inside most items of
electronics and you will find fuses, often special ones designed to
protect the components.
For example, thyristor or triac devices should use a fuse such as an SGS
type. These are sand filled ceramic bodied fuses and inside there are
multiple wires, four on the SGS types that I used to use back in the 60s.
The idea is that this type would open circuit much faster than a single
strand, with the sand quenching any arc that might occur.
Purely as a matter of interest the best fuse I have ever come across,
cheap and blew faster than anything else known was a water fuse. This
consisted of a jam jar, a piece of wood with two nails hammered in about 2
inches (50mm) apart. A wire was soldered to each nail and was wired
within the circuit you needed to protect. A very thin strand of tinned
copper wire is then strung between the two nails.
The jam jar was filled with cold water and the wood placed on the jam jar
with the nails dunked in the water. When an overload occurred the wire
would heat up and displace the surrounding water by steam. In this
situation you then effectively had an underrated piece of fuse wire in
free, almost, air and it would melt very rapidly. As it did so the water
would rapidly fill the gap quenching any arc that might occur.
You may wonder what sort of running currents we were using and the actual
gauge of wire we used. For running currents up to about 10A we used
0.0076 inch wire. Increased currents? Simply increase the number of
strands. We used this on static inverters up to 200V 100 amps DC, running
current. This being the power supply feeding a bridge of thyristors on a
500Hz unit.
Please don't mention any of this to your health and safety inspectors!
73
Brian G3OYU
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