[TowerTalk] Control and coax cable removal question

[Jim Brown]

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