K3: Added protection for RS-232 port

[Joe Subich, W4TV-4]

 > A quick look at the ASTRON RS-35 skematic seems to indicate that the
 > negative terminal is connected to the neutral and chassis ground.

You misread the schematic.  There is no connection between the neutral
and ground.  Both sides of the transformer "float" - only the third
wire (safety ground) connects to the chassis on the primary side of the
transformer.  See;
http://www.repeater-builder.com/astron/pix/astron-rs35m-2000-01.jpg

None of the Astron schematics I've check show the neutral (either
side of the 120V primary) connected to the chassis.

 > Thus if you connect ur rig ground terminal to an earth ground, you
 > are also connecting it to the neutral.

Not it your rig complies with UL and NEC rules.  The neutral CAN NOT
be connected to the chassis.  On the primary (line) side of any
transformer the only conductor that can be connected to the chassis
is the GROUND (third wire, round pin) of the 120V line.  If the
device is rated for 240V operation, the only wire that may (and is
required) be connected to the chassis is the FOURTH wire.  The
neutral (if used) MAY NOT be connected to the chassis/frame of ANY
device (radio, appliance, etc.).

Again, the *ONLY* permissible connection between neutral and ground
is at the primary load center (main breaker panel)/service entrance.
If *ANY* equipment has neutral (as opposed to the safety ground)
connected to the chassis, it not only violates code in every US
jurisdiction, it is a significant - potentially fatal - safety
hazard.

73,

    ... Joe, W4TV

On 7/20/2010 10:56 AM, Brian Alsop wrote:

> Correct me if I am wrong.
>
> It appears that one is doing just this whether he knows it or not.
>
> A quick look at the ASTRON RS-35 skematic seems to indicate that the
> negative terminal is connected to the neutral and chassis ground.
>
> The RS25 power supply even has a ground screw which indeed is connected
> to the chassis, negative side and neutral.
>
> Thus if you connect ur rig ground terminal to an earth ground, you are
> also connecting it to the neutral. Hence, the discussion that has been
> here ad infinitum about connecting the mains ground rod to the station
> earth ground.
>
> 73 de Brian/K3KO
>
> Joe Subich, W4TV wrote:
>
>> *STOP!* NEC requires that neutral be grounded *ONLY* at the
>> entry panel (main breaker box). Neutral is not a substitute
>> for the safety ground (round pin on the 120V outlet) and should
>> never be connected to equipment chassis.
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>> On 7/20/2010 6:26 AM, Pete Smith wrote:
>>> 73, Pete N4ZR
>>>
>>> The World Contest Station Database, updated daily at
>>> www.conteststations.com The Reverse Beacon Network at
>>> http://reversebeacon.net, blog at reversebeacon.blogspot.com, spots
>>> at telnet.reversebeacon.net, port 7000
>>>
>>>
>>> On 7/20/2010 12:01 AM, Don Wilhelm wrote:
>>>> ...so if you wish to protect your K3 correctly (along with all the
>>>> other equipment in your hamshack), install some good lightning
>>>> protection - single ground point entry point for ALL lines coming
>>>> into the hamshack - NO exceptions - ethernet, telco, antennas,
>>>> rotator, control lines, and yes even the AC mains entry to the
>>>> hamshack should enter through a single panel
>>>>
>>> All of my hamshack equipment is on a single outlet. This has me
>>> wondering whether a good quality connection between the entry panel
>>> SPG and the neutral *at the outlet* (it is less than two feet from
>>> the entry panel) would approach or achieve the objective of helping
>>> everything to rise and fall together.
>>>> employing MOV or other protection devices present at that panel for
>>>> each and every line - this is the single most important point of
>>>> lightning protection.
>>>>
>>> Yet other knowledgeable people say that using MOVs in this way is apt
>>> to *cause* damage. I realize that this discussion should probably
>>> move to Towertalk now, but don't want these questions to go unraised,
>>> and we have a bunch of the right people here.
>>>
>>> 73, Pete N4ZR
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