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Re: [TowerTalk] Control and coax cable removal question

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Control and coax cable removal question
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Thu, 15 Oct 2020 10:55:28 -0700
List-post: <mailto:towertalk@contesting.com>
On 10/15/2020 6:05 AM, jimlux wrote:
Most coax has a 300V rated jacket (9913 is 300V, for instance, as is 9258 (RG-8X), LMR-400's datasheet doesn't even give a UL rating)

UL ratings for cable are for flammability, flame spread, and noxious fumes when they burn. They are the result of the real life event upon which "The Flaming Tower" movie was based, when excessive neutral current that resulted from triplen harmonics in vertical cable runs spread through the high rise building.


Romex (NM-B) is 600V, as is the usual THHN building wire.


There's some trickyness with respect to the code in running different voltages. It's not clear that antenna cables are Class 2 wiring - the rule says that Class 1 and Class 2 can't run in the same conduit, unless separated by a continuous barrier (is a second layer of insulation, e.g. Romex, a "continuous barrier"?)

While single phase mains power is nominally 120/240VAC, capacitors for use on mains power wiring must be rated for 3kV/6kV, depending on how they are connected, to withstand voltage transients that result from equipment connecting and disconnecting, and from lightning. It's not the operating voltages, it's the abnormal voltages.

It's been a while since I read the code, but I've specified conduit systems for many sound systems in large and small buildings. Antenna cables are LV wiring, as are audio, video, and most other wiring for small signal circuits. In buildings, LV wiring must be separated from mains power wiring, either by a suitable barrier (as in a cable tray), or in separate conduit.

73, Jim K9YC


725-54(a)(1) lets you put low voltage and high voltage in the same enclosure where the HV is not more than 150 V to ground and "solely to connect to equipment".

The

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