[TowerTalk] 120 v inside conduit

[Ronald C. Barnes]

Time to de lurk...

I have to agree with everyone else here, AC and control lines in the same 
conduit is not really "bad" but "not good".  There are ways to do it, 
around it, but I find the potential problems are not worth the 
convenience.  Run the conduit and put the direct burial romex beside 
it.  Though you may not be interested now, I can envision trying to use the 
coaxial run on the LF experimenter's band and cursing the AC line beside it.

One point I have about PVC conduits with towers though....  a metallic 
underground conduit will provide you with a degree of lightning protection 
/ dissipation.  Case in point....  I was an engineer at a UHF TV station 
with a 1000' tower.  You can imagine what a lightning magnet that 
was.  When the station was built, the Chief Engineer ran 4" PVC conduit 
between the studio and transmitter buildings.  When lightning would strike, 
it would follow the coax shields up to the studio and usually blow out the 
last distribution amp in the chain.  Sometimes it would be worse, but 
that's a topic for another day.

We installed a metallic 4" conduit between the buildings and lo-and-behold, 
the toasted distribution amps were no more.  We figured the lightning was 
following the outside of the conduit now, rather than the coax shields and 
audio drain wires.  Since the conduit had direct contact with earth, it 
would dissipate before it got inside.  Again, there was that one in a 
thousand strike that would shoot this theory down in flames.  I guess if 
the strike is strong enough, no amount of protection will be 100% effective.

So.... for a bit more money, run metallic conduit rather than PVC whenever 
possible, gives you that extra ground and some protection against lightning.

Ron :)   Chief Engineer WSAH TV 43


At 08:11 AM 4/9/00 -0500, you wrote:

>On 4/9 Ken wrote:
><I'm going to put up a tower this summer, I was thinking of running a 120
>VAC line inside the same PVC conduit along with my coax feeds. Any
>problem with this idea?
>Thanks,
>Ken W2DTC>
>
>This is a pet peeve of mine Ken.  Control wires and AC should not be run in
>the same conduit.  Run your coax in the conduit and use a type of Romex that
>is suitable for burying, or make two conduit runs.
>good luck, Tom......KB0MZG
>
>
>
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