Re: [TowerTalk] surge supression

[Jim Lux <jimlux@earthlink.net>]

At 02:22 PM 11/7/2003 -0500, Alan Beagley wrote:
> ISTR reading that *all* grounds must be connected together (according to 
> the National Electrical Code).


Safety grounds yes, but not signal common point references.  No 
requirement, for instance, that the shields of coax that is entirely 
indoors be connected to a common ground. No requirement that the shield of 
a coax line that is carried within another conductive tube (i.e. conduit) 
or where the shield is not being used as a safety grounding conductor be 
tied to "green wire ground". I'd have to go check my code, but I think if 
you ran an explicit lightning dissipation/grounding conductor along side 
the coax, there'd be no requirement that the coax be connected at any point.

In fact, there are situations where the common point power ground (i.e. the 
neutral on a Wye connected 3 phase system) can be isolated or connected to 
ground through a high impedance (to reduce nuisance trips from ground fault 
currents).

There's certainly no requirement that the common RF ground point be 
interconnected to the electrical safety ground. The shield of the coax is 
just another low voltage conductor.  Now, if the coax shield is serving two 
purposes, it's another story.

It all depends on what the function of the "ground" is...
Jim, W6RMK



> Alan AB2OS
>
>
> On 11/07/03 11:02 am Gene Bigham put fingers to keyboard and launched
> the following message into cyberspace:
>
> > I have seen others state that connecting in the house mains ground to the 
> > RF ground is bad idea due to the difference in potential different places 
> > in the circuit end up being in case of a lightening event.

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