[Collins] KWS-1 Line Wiring & WTB: 312A-1

[Dr. Gerald N. Johnson]

Looks like only the high voltage plate transformer gets reconnected for 
240 volts, the other transformers and the control circuits still load 
one side of the 240 volt circuit and return through the neutral. A 
reduced size neutral was based on the expectation of the neutral 
operating current would be leas than the currents in the main conductors 
which is often true, but neglects safety in the case of a short circuit 
at the load. The three wire power cord on 240 leaves out the chassis 
grounding safety conductor so presents the potential for a shock hazard 
if there is any failure of insulation from line to chassis, in the 
wires, the bypass capacitors or a transformer winding. In years past, 
even on a 120 volt outlet a reduced size ground wire compared to the hot 
wire was allowed in the National Electrical Code. That proved to be 
unsafe because a short could burn off that safety ground without opening 
the hot wire, leaving the enclosure of appliance, tool, or radio 
connected directly to the 120v. A serious shock hazard. The reduced size 
safety ground is no longer accepted in new work.

Its not allowed by the modern NEC to return operating current through 
the ground wire and an outlet with a GFCI will absolutely not allow 
that. Load current must return to the panel through the neutral that is 
only connected to ground in the main panel. The ground wire is never 
supposed to carry operating current, only fault current from the load 
device if a short to the case occurs. Its purpose is to protect the 
people around the equipment, not to operate the equipment.

I would recommend a new four conductor power cord, all conductors the 
same 12 gauge (20 amp fuse in the KWS-1) with a four wire outlet and 
circuit to the service panel keeping neutral and safety ground separate 
everywhere beyond the main service panel. Red and black for the two 120 
volt supplies, white for the neutral, and green for the safety ground 
connected securely to the power supply chassis. It won't be original but 
it will be a great deal safer. Current through the line bypass 
capacitors on vintage radios has caused many an annoying tickle when the 
chassis wasn't grounded. Even when they were new and the capacitors 
hadn't gone leaky, a .05 uf capacitor will carry enough current from 120 
that you WILL detect it with a dry finger touching the radio and that's 
not much fun.

The only problem with using a gauge larger conductor is fitting it to 
the connections in the transmitter and the plug. It makes for better 
efficiency by reducing the voltage drop in the cord and that gives 
better voltage regulation at the load. Same thing is true with the wires 
from the panel to the transmitter outlet. Bigger is better, though more 
costly. Watts lost in the wiring don't radiate but cost at the electric 
meter.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 8/22/2015 3:31 PM, Corey Sukalich wrote:
> I’m (finally) looking into setting up my Gold Dust Twins station.  I
> have some questions for those on the list as to how they wired their
> KWS-1.  I’m planning to run a dedicated 240 V circuit for the
> transmitter, but given its age and the wiring changes over the years
> I was curious how they were originally equipped and what (if any)
> safety changes should be made for good measure.  It presently has a
> 240 V, 15 A, 3 wire (grounded) plug and the cord appears to have a
> smaller ground wire than the two hot leads.  On some of the other
> forums I’ve visited there have been lively discussions about properly
> wiring vintage equipment and safety pitfalls of not doing so.  I
> figure since I have to run a new circuit, I should do it right.  I’d
> love to hear any commentary one way or the other about how everyone
> is powering their KWS-1 (or other vintage pieces of similar nature).
>
> Also, since I’m posting I figured that I would express my continued
> interest in finding a 312A-1 (or SC-101) speaker as I have yet to
> acquire one for the station.  Pictures, price, and details
> appreciated on any replies of available gear.
>
> Thanks&  73 Corey, N9WIV
> ______________________________________________________________
>