[Elecraft] [KPA500]KPA500 power cord question

[Clyde Washburn]

Currently the nominal voltages for most US power companies is 240/120V single phase, although in some areas 120/208V 3-phase is
common, with 120V outlets being served by any one phase, and 208V circuits being fed across any 2 phases.  Accordingly, most US
appliances either have specific performance ratings that differ slightly for 208V vs. 240V (resistive heaters and A/C compressors
are a common example), or have power supply taps to accommodate either (common in electronic equipment).

The major advantage of 240V operation is improved voltage regulation:  the same circuit, fed with the same wire (such as a common
20A 12 gauge circuit), will have the same resistance in either case.  But since the current is roughly half at 240V, the I*R drop
will be half, which will be 1/4 the relative amount compared to the doubled voltage.  You can see that unregulated supplies will
perform much better, if the current is high enough for line drop to be noticeable.

US plugs and receptacles are rated for either 125V (max) or 250V (max), and are non-mating between voltages, for safety.  However
20A receptacles of ether voltage will accept 15A plugs of the same voltage, so the ideal hamshack receptacle for a linear is a
250V/20A receptacle wired to a 240V or 208V 20A circuit, which will also accept 15A 250V plugs, the smallest and most common type.
Since 20A wiring and circuit breakers cost very little more than 15A, there is little point in installing 15A circuits, unless it is
advantageous to use existing wiring in an house or building where new wire installation is difficult.  Please note that if you
convert an existing 120V wire run to 208 or 240V, you are obligated by code (and common sense) to remark the white (formerly
neutral) wire with red paint or tape at all points of access, to identify as a "hot" lead.  And receptacle ratings should never
exceed the rating of the circuit they are on:  never use a 20A receptacle on a 15A circuit.

In the specific case of the KPA500, it requires 1000VA (volt-amperes), so that is 8.3A at 120V, 4.8A at 208V, or 4.2A at 240V.  8.3A
is not a particularly heavy load for a 20A circuit, but if it is a 15A circuit or is also loaded with all the other hamshack gear,
then either a separate 120V circuit for the linear, or preferably a 240V circuit is a good idea.  

_____________________
Clyde Washburn, K2UE
82 Lasalle Pkwy
Victor, NY 14564-9610
585-317-7006
k2ue at rochester.rr.com

-----Original Message-----
From: elecraft-bounces at mailman.qth.net [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of iain macdonnell - N6ML
Sent: Tuesday, May 03, 2011 2:21 PM
To: K2GN
Cc: Elecraft - K3
Subject: Re: [Elecraft] [KPA500]KPA500 power cord question

On Tue, May 3, 2011 at 5:59 PM, K2GN <k2gn at k2gn.com> wrote:
> GA,
>
> I am in the process of rebuilding my shack and planning for the future.
>
> I will order a KPA500 and want to be ready for it power wise.
>
> I want to run it on 220V as it is available in a nearby panel.
>
> Question is:
>
> The manual states for 220V operation I would need an adaptor or new 
> plug on the power cord.
>
> Is this a choice that I have as far as wall outlet and matching plug? 
> If so, no problem, my electrician can fix it up.
>
> If it's some special, I need specs for it.

I think that's left as an exercise for you ... find a heavy computer power cord, cut the plug off, and install one that matches your
outlet .. or install a matching pair that you like.

I'd be interested to hear about benefits (if any) of running the
KPA-500 on 220V vs 110V (in the US)......

    ~iain / N6ML
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