[Elecraft] KPA800/1500 Power Question

[Bill Coleman]

On May 26, 2005, at 12:33 PM, Vic Rosenthal wrote:
>
> I don't know the actual power requirements, Jim, but I would expect  
> overall efficiency of around 50%, taking into account the power  
> supply and amplifier efficiency.  However, if you are installing  
> ANY high power amplifier, it's generally thought that a 20-amp 240V  
> circuit is appropriate.

15-amp service is probably sufficient.

>   This is probably more than you will need for a KPA800, which  
> would probably work fine with 15 or perhaps even 10 amp service at  
> 240V, but (depending on the length of the line to your service  
> entrance) it probably means no. 12 wire, which is not a big deal.   
> An electrician can tell you what you need to do to meet code in  
> terms of wire size, type of conduit, type of receptacles, etc.

NEC requires 12-2 for a 20 amp circuit, 14-2 for a 15 amp circuit.

> What I did was install 20 amp breakers and use no. 10 wire to  
> ensure the minimum voltage drop under load.  I brought out 4  
> wires:  two hots, one neutral, and one ground.

Why would you need a neutral? On a 240v circuit, there's only three  
connections - both hot sides and ground.

>   The neutral is ONLY connected to the ground at the service  
> entrance, noplace else.  Most amplifiers only need the two hot  
> leads and ground (there are exceptions).  I use the hot-to-neutral  
> connections to provide two 120v circuits for other shack equipment.

I would not do this. I would run a single 240 volt circuit for the  
amp. If you need other circuits, you can run a separate 120 volt runs  
for them. You really shouldn't have offset neutral runs away from the  
panel like that. I'm pretty sure that's not to code. (Consider what  
would happen if the neutral line from the panel to your 120v circuits  
should open in that case)

In my current basement shack (which I wired myself), I have two  
separate 120v (14-2) circuits feeding a total of 10 outlets (with  
GFI), a separate 240v (14-2) circuit for the (future) amp, and a  
forth circuit that feeds the lighting (which is shared with another  
room). (Its generally good practice to run lighting and outlet  
circuits separately)

> I would not run a 1KW amp on a 120v line if I could avoid it, due  
> to the greater voltage drop that would be incurred.  I understand  
> that the KPA800 is capable of 1000w or more output on CW (it's  
> limited to 800w on SSB due to increased IMD at higher power levels).

Agreed. A 15-amp 240v circuit should do it, or you can go to 20-amps.  
(It is sometimes easier to find a 20-amp dual-gang breaker than a 15- 
amp. Size the breaker according to the wiring used)

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901