[Elecraft] Grounding negative side of power supply?

[Joe Subich, W4TV]

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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