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Re: [TowerTalk] Grounding

To: "'Jim Lux'" <>, <>
Subject: Re: [TowerTalk] Grounding
From: "Gary Schafer" <>
Date: Sat, 17 Nov 2012 12:56:15 -0500
List-post: <">>
The main reason to cadweld connections is to ensure a good connection over
Yes you can get a very good connection between rod and cable with the brass
clamps and get a much lower resistance connection than the ground rod itself
gives to earth. But the clamp can not be assured of a good connection over
long periods of time compared to a cadweld.
All ground connections should be checked and serviced at regular intervals,
but how many actually do that.

A low resistance connection to a ground rod is not near as important as it
is in other connections of your single point system. There you want a very
low resistance connection in order to maintain low voltage differences
between equipment, supply lines, antenna cables etc.
A few tenths of an ohm can cause a huge voltage difference when thousands of
amps of strike current are passing by.

Gary  K4FMX

> -----Original Message-----
> From: TowerTalk [] On Behalf Of
> Jim Lux
> Sent: Saturday, November 17, 2012 10:51 AM
> To:
> Subject: Re: [TowerTalk] Grounding
> On 11/17/12 4:40 AM, K1TTT wrote:
> >> Dale - WD4IFR
> >> In any lightning strike, even a 2" solid piece of copper takes on the
> >> characteristics of a light bulb filament.
> >
> > It is simple statements like this that make the rest of what you say
> > questionable.  The fact is that MOST lightning strokes hitting even
> small
> > conductors will not significantly heat them.  To get any significant
> warmth
> > in 2" copper is probably even beyond even the largest measured mega
> strokes.
> I agree... take a look at the Preece or Onderdonk equations for fusing
> current.  Onderdonk takes into account the pulse length.
> >> BTW -- You do not have to use exothermic welds exclusively for your
> >> ground connections.  One of the companies that make crimp on
> grounding
> >> connectors is "Burndy".  These clamps are designed to get away from
> >> Cadwelding but still require the use of a 12 ton crimper to bond the
> >
> > I have never cadwelded a ground connection, most commercial
> electricians I
> > know would probably look at you with complete confusion if you asked
> them to
> > do that.  The basic brass clamp sold in every hardware store is what
> > probably 99% of the ground connections in this country are connected
> with is
> > just fine.  After all a discharge that has just jumped a mile to the
> ground
> > isn't going to be stopped by a few microns of oxide in a connection
> between
> > two conductors.  Even lightning rod installers use easily hand crimped
> > splices and connectors.
> the need for exothermic welding or good clamps isn't for lightning.  As
> 'TTT says, a few thousandths of an inch gap or oxide isn't going to make
> any difference.
> The good quality bond is for more mundane electrical safety reasons,
> when the 110V wire shorts to the metal case, you want the circuit
> breaker to trip, or, at least, the voltage on the case relative to your
> bare feet to be limited.
> >
> >
> > Oh, one more while I'm at it:
> >
> >> copper braid that are cadwelded (exothermic) to the tower legs.  From
> >
> > Braid?? Cadwelded??  I always thought this was a no-no.  and who runs
> braid
> > for a lightning or safety ground?  Don't all codes specify solid
> conductors?
> You can use stranded in larger sizes. There's a lot of 2/0 stranded used
> for this kind of application, for instance.  (because handling solid 2/0
> is hard work?)
> I'm too lazy to go get my code book and check, but there IS some
> threshold size for it.
> I wouldn't use welding cable (zillions of tiny strands, so it's real
> flexible).  I had bad luck using welding cable for pulsed power
> applications, although I never spent much time figuring out why.
> > I wouldn't trust braid for an outdoor application like that anywhere,
> unless
> > maybe you are talking about braid that uses something  like 10ga
> strands.
> AWG 2/0 stranded...19 strands of something like 16.
> >
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