KPA500 - ground wire between the AC earth and RF output socket

[Johnny Siu]

Hello Group,
 
On page 19 of the KPA500 kit assembly instruction, there is a green ground wire connecting between the AC Earth terminal and the case of the RF output socket.  It is my first time to see such a ground wire design.  Is there any specific reason for doing that?
 
Thank for your advice in advance.

TNX & 73,


Johnny VR2XMC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[Jim Brown-10]

On 9/4/2011 6:52 AM, Johnny Siu wrote:
> On page 19 of the KPA500 kit assembly instruction, there is a green ground wire connecting between the AC Earth terminal and the case of the RF output socket.  It is my first time to see such a ground wire design.  Is there any specific reason for doing that?

This is a requirement of most electrical safety codes worldwide -- that
is, the AC green wire MUST be bonded directly to the equipment
enclosure. It is also good engineering practice.  See the tutorial on
Power and Grounding that is on my website.
http://audiosystemsgroup.com/publish.htm

73, Jim Brown K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[roncasa]

> This is a requirement of most electrical safety codes worldwide -- that
> is, the AC green wire MUST be bonded directly to the equipment
> enclosure. It is also good engineering practice.  See the tutorial on
> Power and Grounding that is on my website.
> http://audiosystemsgroup.com/publish.htm



I have not seen the manual mentioned in this thread, and
I may be unclear regarding this, but as all ham radios derive power from
their separate power supply, isn't the "switch-mode" type isolated?

then the required "green wire" in the AC line should be tied to the
power supply, not the radio.

Please correct me if I'm wrong.

72
Ron, wb1hga
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[Mark Bayern]

>>"then the required "green wire" in the AC line should be tied to the
power supply, not the radio.

I think we have missed the point. Any line powered device that has a
conductive enclosure should have that enclosure bonded to the 'green wire'.
It is a personnel safety issue. The KPA500 is line powered and has a metal
enclosure.

I see Jim's white paper does a good job of explaining this <
http://audiosystemsgroup.com/SurgeXPowerGround.pdf>. The grounding
discussion starts on page 10. The bottom of page 11 directly addresses this
issue, but the complete discussion is very good.

Mark  AD5SS
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[Rick Dettinger-3]

A power supply transformer can't be considered to be totally isolating  
for safety purposes unless there is a shield between the primary and  
the secondary that is grounded to the primary.  Some marine shore  
power isolating transformers have this shield, but they are quite  
expensive and not usually used.  Without the shield, there is a  
possibility for an internal short that would tie the secondary  
directly into the AC mains.  Thus, the rig that is powered by the  
supply needs to be grounded to the AC ground system.

73,

Rick Dettinger   K7MW

>
>
> I have not seen the manual mentioned in this thread, and
> I may be unclear regarding this, but as all ham radios derive power  
> from
> their separate power supply, isn't the "switch-mode" type isolated?
>
> then the required "green wire" in the AC line should be tied to the
> power supply, not the radio.
>
> Please correct me if I'm wrong.
>
> 72
> Ron, wb1hga
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[Johnny Siu]

Hello Jim,
 
Thanks for your reply.
 
Yes, I understand the rationale behind.  However, I don't understand why the green ground wire is so specifically linking the AC Earth Terminal to the case of RF output socket instead of other metal part of the KPA500.  Could you please enlighten me on that?
 
I have another question.  I live in a multi-storey apartment.  Split-type airconditioners are everywhere so that man made RFI can come to my radio / linear amplifier via the AC Earth.  To avoid this, can I put RF choke between the AC Earth and the ground (i.e. metal case) of the KPA500 ?

TNX & 73,


Johnny VR2XMC

從︰ Jim Brown <[hidden email]>
收件人︰ [hidden email]
傳送日期︰ 2011年09月5日 (週一) 2:04 AM
主題︰ Re: [Elecraft] KPA500 - ground wire between the AC earth and RF output socket

On 9/4/2011 6:52 AM, Johnny Siu wrote:
> On page 19 of the KPA500 kit assembly instruction, there is a green ground wire connecting between the AC Earth terminal and the case of the RF output socket.  It is my first time to see such a ground wire design.  Is there any specific reason for doing that?

This is a requirement of most electrical safety codes worldwide -- that
is, the AC green wire MUST be bonded directly to the equipment
enclosure. It is also good engineering practice.  See the tutorial on
Power and Grounding that is on my website.
http://audiosystemsgroup.com/publish.htm

73, Jim Brown K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[Jim Brown-10]

On 9/4/2011 5:22 PM, Johnny Siu wrote:
> Hello Jim,
> Thanks for your reply.
> Yes, I understand the rationale behind.  However, I don't understand
> why the green ground wire is so specifically linking the AC Earth
> Terminal to the case of RF output socket instead of other metal part
> of the KPA500.  Could you please enlighten me on that?

That's a question that really relates to the internal design of the KPA
itself.  The concern is what happens in the case of a lightning strike,
which is usually strongest on antennas and on the power line. They can
generate strong currents, and a good design for earth and chassis
bonding will try to have those currents stay outside the box -- that is,
not flowing through the circuit boards or the chassis. The best way to
do that is to have those external wires bonded to the same physical point.

> I have another question.  I live in a multi-storey apartment.  
> Split-type airconditioners are everywhere so that man made RFI can
> come to my radio / linear amplifier via the AC Earth.  To avoid this,
> can I put RF choke between the AC Earth and the ground (i..e. metal
> case) of the KPA500 ?

NO!  This defeats the safety of the bonding for lightning protection!  
What you CAN do is implement proper bonding of your power system,
carefully following the rules in your country.  My tutorial primarily
addresses the rules in North America, and there are some variations from
one country to another. But the general rule that works everywhere is
that everything must be bonded together by the shortest practical path
-- all ground electrodes (rods), building steel, power system neutral
(at the entry panel), radio equipment, arrestors for telephone and cable
TV, etc.  Again, study the tutorial.  As it turns out, the SAFEST
bonding is also the QUIETEST bonding.

Another important point.  If you're using any sort of long wire antenna,
whatever your chassis is connected to is an important part of the
antenna -- the return current of the antenna has to go SOMEWHERE.  If
you open that circuit (with an RF choke), you may hear less noise, but
the antenna won't transmit nearly as well.  If you're using a coax-fed
antenna, you CAN add a common mode choke to it to kill the noise picked
up on the coax.  See my RFI tutorial for details on that.

73, Jim K9YC


______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html