W2IRT asked:
Questions:
1) How far below ground should I run these wires? I'm just using
hand-tools to trench, not a ditch-witch, so the plan was about 3 or 4
inches.
You can get a little help from conduction of the bare wire to the
surrounding ground. The top layer of soil (at least around here) tends
to dry out a lot, and when that happens the conductivity drops, so a
little deeper would be better. It's difficult to determine exactly what
the difference would be, but if you already have enough ground rods it
may not be worth the effort.
-----------------------------
2) Polyphasers. This is a big question mark. Most things I've read
say to mount 'em all on a single-point panel inside the house,
strapped with a 2" or 3" copper bus to a ground rod outside the
house, which in turn is connected to the ground rod system. I 've
seen lots of pics online of polyphasers outside, in a NEMA box on
a tower leg, others saying I should have them physically connected
to the tower and the top and bottom, AND inside the house on the SPGP
panel, etc.
Outside is usually better because as someone already said, you don't
want the lightning transients coming inside. However your system should
be designed such that the major portion of the lightning current goes
into the ground before it gets to the transient suppressors, so some
amount of variation can be done if you are careful. For example, my box
is inside my garage wall at the floor. Immediately adjacent to that
box, outside, is a ground rod maybe 2 feet away, and the ground rod for
the AC power entrance is 6 feet from that.
The suggestion for transient suppressors at the tower and just outside
the house was for long runs (which you don't have). The coax shields
should be connected to the tower at the top and bottom, and of course
they will be connected to ground at the suppressor box at the house.
------------------------
3) TVSS (transient voltage surge suppressors): Yes? No? Maybe??
For me, yes. There are guys that don't use them and rely on good
grounding to remove the transients, and some are successful at this, but
for me it's a small price to pay for extra protection. Note that
without suppressors long antennas (80 & 160) will still require some way
to get rid of the static charge.
---------------------
Guys, am I over-thinking this or over-engineering this project for a
70; crankup?? I've got 3 trees higher than that on the property, as
do most of my neighbours, 250kV transmission lines at the end of the
street and a 20 year history of never taking a direct hit at this
house (100' tower by the previous owner with one ground rod and 4 GA
round green wire). the only lightning hit that did anything came in
on the power line as a surge that cooked my motherboard on the radio
PC, despite an APC UPS.
If your time is as cheap as mine, it pays to over-engineer it. Remember
that a hit on your antenna is not all you have to worry about. A hit on
those power lines may sent transients into your house, and you don't
want your radio stuff to be sitting at zero volts when thousands of
volts enters common mode on the power lines. Also think about all the
other lines entering your house (phone line, TV cable, whatever. Is your
water line copper or PVC?). You want all these to be tied into the same
ground system so that everything goes up and down together.
Jerry, K4SAV
Peter Dougherty wrote:
>Hi all,
>
>Getting ready to put my ground system in shortly but will be shopping
>for Polyphasers, etc at Hamvention next week.
>
>Here's what I have. One 70' crank-up tower about 5 feet from the back
>wall of my house. I've driven in a bunch of ground rods ~16 apart
>(most are down all 8', some only 5 feet due to rocky soil, however)
>going around my house on 3 sides. The fourth side is a paved
>driveway, so that's not happening any time soon. It will eventually
>connect to the service panel once I can get an electrician to come by
>and hook it up, per NJ code.
>
>I also have a bunch of Cadweld one-shots for AWG-4, but I haven't
>purchased the wire yet. I'm guessing AWG #4 solid is the right choice
>for this application? Given copper prices, 2-gauge is too expensive.
>
>Questions:
>1) How far below ground should I run these wires? I'm just using
>hand-tools to trench, not a ditch-witch, so the plan was about 3 or 4 inches.
>
>2) Polyphasers. This is a big question mark. Most things I've read
>say to mount 'em all on a single-point panel inside the house,
>strapped with a 2" or 3" copper bus to a ground rod outside the
>house, which in turn is connected to the ground rod system. I 've
>seen lots of pics online of polyphasers outside, in a NEMA box on
>a tower leg, others saying I should have them physically connected
>to the tower and the top and bottom, AND inside the house on the SPGP
>panel, etc.
>
>3) TVSS (transient voltage surge suppressors): Yes? No? Maybe??
>
>Guys, am I over-thinking this or over-engineering this project for a
>70; crankup?? I've got 3 trees higher than that on the property, as
>do most of my neighbours, 250kV transmission lines at the end of the
>street and a 20 year history of never taking a direct hit at this
>house (100' tower by the previous owner with one ground rod and 4 GA
>round green wire). the only lightning hit that did anything came in
>on the power line as a surge that cooked my motherboard on the radio
>PC, despite an APC UPS.
>
>I'll be at the lightning panel in Dayton next week (probably asking a
>lot of questions afterwards, too), but can always use more guidance.
>
>
>
>Cheers,
>
>Peter,
>W2IRT
>
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>
>
>
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>
>
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