[Elecraft] KPA500 Voltage?

[Jim Brown]

On 11/14/2022 1:43 PM, Ed Cole wrote:
> That is rated for 90A (in general).  Resistance is 0.318 ohms/1000-feet 
> so my 120-foot run has 0.0382 ohms.  At 50A this results in a voltage 
> drop of 1.9v.  My service voltage is 243VAC.

It's important to realize that current on AC mains is FAR from being a 
sine wave. This has been true for at least 30 years, as loads have been 
strongly dominated by switch-mode power supplies in almost every piece 
of equipment wiring into or plugged into, the system, and square-wave 
modulated controllers for nearly all large loads, like motors and 
heating devices. Current flows in pulses, usually short ones, that 
recharge the input capacitors of associated power supplies.

The result of this is that both IR drop and the resulting heating are at 
least one-third greater than predicted by Ohm's Law applied to a sine 
wave. It is, therefore, very good engineering practice to oversize 
conductors, as you have done! Before we moved into the home we bought in 
NorCal, I had the outbuilding housing my shack rewired, and even though 
the runs from the panelboard are pretty short, had #10 pulled in for the 
20A-240V circuit. Since I will never have more than one amp on at a 
time, I felt that 20A was sufficient. All of the 120V circuits are 20A, 
wired with #12, not oversized, since the only heavy load, 1 12A space 
heater, has its own circuit.

73, Jim K9YC

73, Jim K9YC