CADweld is the brand name of the copper thermite mixture for welding
wire to rods. Commercial electrical supply houses stock it (Platt
here). There are many configurations of wire size, rod diameter and
wire orientation so look at the Erico catalog to find the right models.
The "one time use" ceramic molded are the cheapest for the small number
of rods normally in a tower install.
I was skeptical of the upsizing of ground wires to rods in the latest
codes, i.e. #6 > #2. After installing some more rods and measuring
them with a ground resistance meter I think the larger diameter wire is
essentially a horizontal rod with rods spaced 2x their length. I've
also measured the resistances 3 times - very dry soil, saturated soil,
and frozen soil, the total ground rod resistance was 7.9, 5.3 and 6.6
ohms respectively, all below the recommended 10 ohms or less in the
code. Besides the obvious that wet earth is more conductive it seems
frozen earth is less conductive (makes sense as ice is less conductive
than water). So "next time" I would bury the top of the rods and the #2
wire below the frost line (only about 1 foot here). The "average" rod
is about 60 ohms as is the Ufer in the 4x6' concrete floor of the shack
at the base of the tower. 60 ohms seems in the ballpark for rods in
average ground.
I bought a Duoyi DY1000A Ground Resistance Tester, cost about half of
what I could rent one for and 1/10 of what Greenlee wants. It seems to
be very repeatable and comes with a cal loop. For $10 more this model
does more
http://www.ebay.com/itm/DUOYI-Leakage-Current-And-Grounding-Resistance-Clamp-on-Earth-Tester-DY1200-/321969345083?hash=item4af6de523b:g:I3MAAOxy69JTDW~A
One thing in laying out rods is to have the wires in a radial (star)
connection to the tower, no loops or cross connections. Then each rod
or string of rods can be measured (actually it is a little more
complicated than that, it's explained in the manual).
Grant KZ1W
On 1/9/2016 10:52 AM, StellarCAT wrote:
good point... maybe make the spacing from the tower closer to 6 or
even 8'. I don't know if you can overkill it as long as you take into
account the possibility of current saturation in the soil - for the
cost of 3 ground rods and some #3 or #4 wire I'd rather chance the
overkill then not.
I just did a Google search and it appears the thicker coatings on the
copper (10 mils is standard) outlasts the 3.9mil coating on galvanized
~40 years to 10-15. So seems copper is the way to go (also they're
higher tensile strength - ~58K vs > 90K for the copper).
Gary
-----Original Message----- From: Kelly Taylor
Sent: Saturday, January 9, 2016 1:47 PM
To: StellarCAT
Cc: tower
Subject: Re: [TowerTalk] copper or galvanized ground rods in red SC clay
Here's an interesting question: if the concrete base is an effective
ground connection, do you get more value by placing the rods a rod
length away from the base?
If the idea of separation is to prevent saturation during a strike,
isn't the base and rod combo at risk of saturation if the rods are too
close to the base?
73, Kelly
ve4xt
Sent from my iPhone
On Jan 9, 2016, at 12:41 PM, StellarCAT <rxdesign@ssvecnet.com> wrote:
Just curious if anyone has experience using either of these over a
number of years – whether they’re ‘eaten away’ one any faster than
the other.
Also the conductivity issue – not sure if it matters all that much
for lightning protection. Don’t know if you can ‘weld’ copper wire to
the galvanized ones using the welding devices (can’t remember what
they’re called at the moment).
Finally: with 3 on a tower – one on each leg – the rule is to
separate them by their length correct? So if I have 3 each on about
5’ of wire from the tower that would mean each would be over 8’
(8.66’) from each other .... this is correct – spaced at least equal
to their length (depth)?
Gary
K9RX
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