Hi Barry,
> While I've never had the need to run 120 VAC to the tower, I don't
> understand what the big deal is AS LONG AS IT'S DONE RIGHT. Meaning,
> have an electrician do it, or follow the NEC yourself.
NEC doesn't consider many problems that affect us.
120 vac lines have a tendency to carry noise from things that spark and
arc. They also carry garbage from switching supplies and digital devices.
120 v lines are very difficult to bypass (you should use UL-CSA rated
components), and if a bypass fails or moisture gets in the control or relay
box 120 v can do nastier things to receivers and people than 12 or 24
volts.
120 v relays also generate BIG spikes when opened. It's tougher to
back-pulse limit AC devices, and 120 volts is tougher on small switch
contacts. Control wires are often exposed or poorly protected at various
locations.
> I have an inground pool with 240 VAC running to the pump motor, and
> 120 VAC lights in the pool where the wires actually run thru a water
> filled conduit to the junction box (above ground and water level!) It
> was done the way it should have been (by an electrician), and I'm still
> hear to speak about it.
But you don't receive on your swimming pool, or switch the lines with a
small switch in your ham station over and over again! I used 120 volts to
power a rotor (Telrex 1/3 hp ac motor), but I still ran 24 vdc control
voltages to tower mounted contactors in a weather tight grounded box.
IMO 120 v control lines are not safe or desirable in this application, no
matter how they are designed. Sooner or later someone will get their
fingers across the lines, or the 120 v will get into something it
shouldn't. It's nicer being able to just route the control leads with low
voltage wiring, even furnace and doorbell manufacturers seem to agree.
73 Tom
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|