[Elecraft] Grounding negative side of power supply?

[Don Wilhelm]

Joe,

That is *one* reason *any* ground rod should be tied back to the utility 
ground stake.  It is as requirement of NEC, and should not be ignored.  
If you drive ground rods for the ham station, connect those ground rods 
to the utility entrance ground rod - no exceptions.  The ideal is #6 or 
larger wire, but if you cannot do that use whatever wire you can.  Your 
safety depends on it.  If you cannot connect extra ground rods to the AC 
mains entry ground, then do not drive those extra ground rods - they are 
*not* an RF ground (see my many posts in the archives on that topic) - 
and as Joe points out, in the event of a lightning strike (or equipment 
fault), they may create a dangerous condition.

You have 3 "grounds" to consider in the hamshack - 1) The AC safety 
ground,  2) The lightning path ground, and 3) The RF ground.
1) and 2) may be one and the same, but 3) is a "horse of a different 
color", and has nothing to do with a "mother earth" ground - it is a 
point of low impedance at the frequency of interest, and usually exists 
at some point in the antenna system, quite apart from "mother earth".  
The English folks have the language a bit better and refer to "earthing" 
which is often apart from "grounding", but we here in the US use the 
same term for all common connections and in the process create confusion 
for ourselves.

73,
Don W3FPR

Joe Subich, W4TV wrote:
> This creates a situation that is potentially hazardous 
> to your equipment.  The AC "third (green) wire" is supposed 
> to be connected to ground only at the main panel/service 
> entrance.  However, since it is connected to the chassis 
> of the power supply, it is also connected through the power 
> supply and radio to ground via the coaxial cable. 
>
> If the point at which the coaxial cables enter the building 
> is not the same place that power enters the building, any 
> nearby lightning strike can set up a significant difference 
> in voltage between the power line "safety ground" and the 
> RF ground (feedline shields/tower).  That difference can 
> fry any electronics connected to both "grounds." 
>
> There are techniques for dealing with this problem ... but 
> they are not necessarily easy or inexpensive. 
>
> 73, 
>
>    ... Joe, W4TV 
>   
>
>  
>
>
>   
>> -----Original Message-----
>> From: elecraft-bounces at mailman.qth.net 
>> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Don Wilhelm
>> Sent: Wednesday, January 20, 2010 8:01 PM
>> To: David Woolley (E.L)
>> Cc: Rich; elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] Grounding negative side of power supply?
>>
>>
>> The AC side should always be connected to the power supply chassis - 
>> unless it is of the "double insulated" design where no ungrounded 
>> metallic part can come into contact with the human body.  
>> Yes, cutting 
>> the AC "green wire ground" is a dangerous thing indeed - the entire 
>> chassis could rise to the AC mains voltage in the event of a fault.
>>
>> The power supply negative *can* certainly be floating *if* 
>> the designer 
>> made provisions for doing that.  It requires that all the common 
>> connections on the secondary side of the transformer are 
>> isolated from 
>> ground.  As I recall, Astrons are not built that way.
>>
>> 73,
>> Don W3FPR
>>
>> David Woolley (E.L) wrote:
>>     
>>> Rich wrote:
>>>   
>>>       
>>>> I had a situation with an older (analog) power supply 
>>>>         
>> (that had its 
>>     
>>>> negative side grounded to the main AC ground) that tripped 
>>>>         
>> the Ground 
>>     
>>>> Fault Circuit Interrupter (GFCI) in one of the bathrooms.  
>>>> Eliminating the bond to ground
>>>>     
>>>>         
>>> I consider this dangerous advice.  If you have an ELCB 
>>>       
>> tripping, you 
>>     
>>> do
>>> not treat the problem symptomatically, by creating an 
>>>       
>> unsafer system, 
>>     
>>> you find out what the real problem is and you fix it.
>>>
>>> I can't tell what the exact wiring configuration is here, but it is 
>>> very
>>> likely that you have created a situation where there are 
>>>       
>> pieces of metal 
>>     
>>> in reach which have low impedance paths to very different "earths".
>>>   
>>>
>>>       
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>
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