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>> Roughly double your standard 13A cable would do... Look at the cable
>> going to the starter motor on your car, that's usually 100A or so.
>
> 1. A car runs on 12V electrics, not 250V. Does that make a difference?
No, the wire has to be the right thickness for the *current*, voltage
doesn't make any difference to its current carrying capability. That's why
the power grid is at a stupidly high voltage, so that current is lower (for
the same power) and hence the cables can be thinner and less power wasted by
heat.
> 2. Is maximum load proportional to diameter or cross section area? (The
> latter is quadratically propertional to diameter.)
Cross-sectional area. IIRC the definition of resistance is something like
material_resistivity*length/x-sec_area. If the resistance of a cable is too
high, then it will get too hot and melt. Heat dissipated is I^2*R...
> Apparently the planners have access to an A0 printer. I don't even want to
> imagine what that must cost... ;-)
Not *that* much, they just print on a roll of paper and work like an
inkjet - just a bit wider :-)
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>>> Like I said, when they hook up the external generator, it comes with a
>>> cable well over 10 cm thick (!)
>>
>> A lot of that thickness will be insulation, shielding and armor.
>
> Probably.
It will probably be 3-phase as well if you are running large bits of lab
equipment...
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>> Yeah, but that's little compensation if as a result businesses stop using
>> you and you fold
>
> I don't think you understand what I mean by "absurd amounts of money". ;-)
>
> [As in, like, if companies *did* stop using us, we'd *still* have so much
> money it wouldn't even matter...]
But what are you going to do with all the money if nobody uses you anymore
because of your reputation of shoddy back-up plans? How long will that
money last paying everyones salaries? ;-)
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scott wrote:
>>> Yeah, but that's little compensation if as a result businesses stop
>>> using you and you fold
>>
>> I don't think you understand what I mean by "absurd amounts of money".
>> ;-)
>>
>> [As in, like, if companies *did* stop using us, we'd *still* have so
>> much money it wouldn't even matter...]
>
> But what are you going to do with all the money if nobody uses you
> anymore because of your reputation of shoddy back-up plans? How long
> will that money last paying everyones salaries? ;-)
Well, it's not really my field, but presumably the people responsible
for this stuff have looked into it quite thoroughly. ;-)
FWIW, we had a freezer fault over the weekend... Interesting coincidence.
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Phil Cook wrote:
> And lo on Fri, 09 Nov 2007 16:08:36 -0000, Invisible <voi### [at] dev null> did
> spake, saying:
>
>> Well, I'm sure somebody will have looked at that and decided it's not
>> worth it. (I would think that for more than 3 seconds of cover, you'd
>> need a battery larger than our entire office...)
>
> You'd think.
Well, 6 mass spectrometers using 450 V electrics... That's gotta eat
juice like candy. If you just wanted to power the freezers, that's
probably quite reasonably - the compressor doesn't even have a 100% duty
cycle, and it's only a small electric motor after all.
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>> But what are you going to do with all the money if nobody uses you
>> anymore because of your reputation of shoddy back-up plans? How long
>> will that money last paying everyones salaries? ;-)
>
> Well, it's not really my field, but presumably the people responsible for
> this stuff have looked into it quite thoroughly. ;-)
Yeh you'd hope so. Presumably if the penalty amount is high enough, CAT
would hire a helicopter or something to get you the generator on time (if it
came to that) :-)
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scott wrote:
>>>> Like I said, when they hook up the external generator, it comes with a
>>>> cable well over 10 cm thick (!)
>>>
>>> A lot of that thickness will be insulation, shielding and armor.
>>
>> Probably.
>
> It will probably be 3-phase as well if you are running large bits of lab
> equipment...
>
Never ceases to amaze me how thick 3-phase power cables appear, yet cut
one open, and the wires encased in the cable aren't *that* thick, but
there's a ton of "wadding" around the actual wires inside the cable.
Extra fun when attempting to unplug a 3-phase device for the first time.
I had no idea it had to twist-on.
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> Never ceases to amaze me how thick 3-phase power cables appear, yet cut
> one open, and the wires encased in the cable aren't *that* thick, but
> there's a ton of "wadding" around the actual wires inside the cable. Extra
> fun when attempting to unplug a 3-phase device for the first time. I had
> no idea it had to twist-on.
Yeh, we had this oven that was 3-phase, but only something like 23A.
However, like you say, the cable was about 10x wider than a normal 13A mains
cable, so cross-section 100x bigger. I didn't see inside the cable, but I
guess it was mostly shielding, armour and insulation...
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Darren New wrote:
> Tor Olav Kristensen wrote:
>>> 2. Is maximum load proportional to diameter or cross section area? (The
>>> latter is quadratically propertional to diameter.)
>>
>> Cross section area.
>
> Also depends on AC vs DC.
At 50 Hz, does it matter?
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scott nous apporta ses lumieres en ce 2007/11/12 09:18:
>> Never ceases to amaze me how thick 3-phase power cables appear, yet
>> cut one open, and the wires encased in the cable aren't *that* thick,
>> but there's a ton of "wadding" around the actual wires inside the
>> cable. Extra fun when attempting to unplug a 3-phase device for the
>> first time. I had no idea it had to twist-on.
>
> Yeh, we had this oven that was 3-phase, but only something like 23A.
> However, like you say, the cable was about 10x wider than a normal 13A
> mains cable, so cross-section 100x bigger. I didn't see inside the
> cable, but I guess it was mostly shielding, armour and insulation...
>
>
Each individual live whire is isulated, then there is a metal mesh protection,
then an outer protective layer. Then, there is a ground (not isolated) and
possibly a neutral whire. The neutral is also isolated and protected by a metal
mesh. The whole thing is paded with ropes, encassed in an additional isolating
layer, then 1 to 5 metal mesh armouring, plus, possibly a metal sheet shelding,
all wrapt in an outer PVC or polypropylen outer shell.
It all adds up.
--
Alain
-------------------------------------------------
When the bosses talk about improving productivity, they are never talking about
themselves.
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