|To:||Alan Beagley <email@example.com>,Gene Bigham <firstname.lastname@example.org>|
|Subject:||Re: [TowerTalk] surge supression|
|From:||Jim Lux <email@example.com>|
|Date:||Fri, 07 Nov 2003 12:04:27 -0800|
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
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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