Hi Dave, many of our linear amplifiers use capacitor filters in the hv power
supply. These type power supplies require peak currents on the order of five
to ten times the average current. While #12 wire may appear adequate based
on average current requirements, the voltage drop in the wiring will be much
more than expected.
I suggest you add up all of the expected amplifier loads and multiply by ten
to derive the peak current requirements. Then look up the resistance per
foot of the size wire you plan to use to determine the total loop resistance.
Multiply the peak current times the loop resistance and you will have the peak
voltage drop in the circuit. If you are satisfied with the number, then great;
otherwise you can try another size wire and recalculate.
A side note is that the power loss in the wiring is related to current
squared so that is another consideration for choosing the wire size. Some power
loss is no big deal but at the current cost of electricity why throw it away
needlessly?
I recently "discovered" voltage drop issues in my own shack, finding that
#10 wiring was dropping about ten volts while running an inefficient 23cm power
amplifier. Referring to a copper wire table in a Radio Handbook is see that
#10 is rated for 6.9 amps at 1500 circular mils per amp. For the 25 amp load
for the 23cm amplifier #4 wire is about right and would have a drop of about
2.5vac in my case. I had a spare length of 4/0 aluminum cable and am
temporarily using that until I get a chance to install the proper cable. The
voltage
drop with the 4/0 cable is negligible and the power output of the 23cm
amplifier is quite a bit higher due to increased key down plate voltage and
increased drive power from the driver amplifier that was also suffering
excessive ac
line voltage drop.
I would be surprised if very many electricians are fully aware of these
issues.
73,
Gerald K5GW
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