Hello Louie:
You are exactly correct in my opinion.
The current rating for any given conductor, has everything to do with the
insulation system which is utilized. The codes do not recognize what
appliances or electronic devices will be fed by the branch circuits. If the
insulation system is polyethylene, and is rated at 60 degrees C., then the
current maximum required to keep the conductor system well below that
temperature is given as the rating.
That is to say for example, that in aircraft and spacecraft applications,
where weight is at a premium, much smaller conductors carry very high
currents. This is accomplished by using expensive flouropolymer insulation
systems (teflon), with very thin insulation wall thicknesses, with
temperature ratings as high as 260 degrees C, utilizing nickel plated copper
conductors or copper alloys, to avoid oxidation and corrosion at those
higher operating temperatures. Some circuits may be rated at only 150
degrees C., if they contain tin plated copper wires. The silver plated
conductors used extensively in fighter aircraft are rated at 200 degrees C.
Conductors which have no insulation system at all, such as buss bar types,
generally run quite warm also.
Start up transient currents have little to do with raising the temperature
of the conductor system.
As stated here before, it is the length of the conductor, and its associated
IR drop, which will determine whether the device being fed operate within
its own electrical parameters. These parameters are the general normal
operating current demands expected for the given load.
We often see the initial sag in voltage from the current inrush, due in
part because the conductors are sized for the normal operation of the
device, rather than for the brief high current transient load. We must
choose our fusing carefully, slow blow, fast blow, delayed, etc., to provide
the appropriate device protection.
If an amplifier requires 20 amperes or less at full output during key down
on CW, and is fed with 12 AWG Copper, with a reasonably short branch circuit
run, the same amplifier on SSB would probably not see very much benefit
while producing 1.5 KW PEP if switched to a 10 AWG circuit, if any benefit
at all. Some slight improvement might be found if the same amplifier was
tested to determine the maximum possible PEP output, but I believe the
difference would be so small, that it could never be detected as a stronger
signal at the receiving end.
73 and Happy Dxing,
Mike
WB2AJI
----- Original Message -----
From: <Gudguyham@aol.com>
To: <aa4lr@arrl.net>; <amps080605@w4zt.com>
Cc: <amps@contesting.com>
Sent: Wednesday, October 19, 2005 10:32 AM
Subject: Re: [Amps] AC wiring
>
> In a message dated 10/18/2005 8:22:50 PM Eastern Daylight Time,
> aa4lr@arrl.net writes:
>
>
> > Now let's try 240 volts
> > which would give us 2944/240=12.3 amps. If your line voltage is
> > low and
> > you have 220 volts the current would be 2944/220=13.4 amps. From this
> > example it is obvious you can't run a full legal limit amp on even
> > a 20
> > amp, #12 wire, 120 volt circuit much less any 120/240 volt, 15 amp #14
> > wire circuit.
>
> Seems to me that 12.3 A and 13.4 A are both less than 15 A. So a #14
> circuit seems adequate for your example.
>
>
>
> FYI....An Ameritron AL-1500 will do 2300 watts output with 100 watts of
> drive. (FACT)
> The AL-1500 comes from the factory with a power cord with a 240V 15A power
> plug and is fitted with 15A fuses. A 240V circuit run to this amp using
#12
> wire will run this amp at 2300 watts out with no problems in SSB and CW
> modes. Surely a 15A circuit will suffice at legal limit. The important
thing
> here is the length of the run from the service panel to the outlet for
the amp.
> If your voltage is way low, the Ameritron has a low voltage tap you can
use
> which ups the secondary voltage so that current again is not an issue.
An
> amp such as an SB-220 can easily be run on a 240 line run with #14 wire.
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