[TowerTalk] Tower grounding?

Mon Jul 20 22:33:20 EDT 2015

Roger,

Good review on grounding and lightning protection !  
I do some of the things you mentioned.  Let me know what you think of my situation.  
All my gear is grounded to a common bus running along the back of my operating desk which receives the ground straps from all the gear.  
When threat of lightning appears  I disconnect the bus from a ground strap that goes out thru the wall and attaches to my ground rods.
Then I disconnect the feedlines and rotor cables and they are pushed thru a square hatch down by the floor and pushed out about 3 feet onto the concrete slab outside.
Then I disconnect the equipment plugs going to two 110VAC receptacles (I have a multiple plug in strip along the back which receives most of the gear, it is unplugged from the 
wall outlet too)  and lastly unplug the amps from two 220VAC receptacles.
My tower is grounded at all three legs to separate ground rods.    The way I do my coax and cables could be better I suppose but until I can come up with something better 
thats what I do.   I don't use lightning arrestors.  Also I usually lower the tower down, it has a motorized winch, (besides lightening I dont want to do wind survival tests with 
my antennas either hihi )  We are having freaky weather here in the SF Bay area now.  Sun shining this morning and this afternoon clouds, thunder and lightning, then back to sun
later in the afternoon. 

Bob
K6UJ

> On Jul 20, 2015, at 5:58 PM, Roger (K8RI) on TT <K8RI-on-TowerTalk at tm.net> wrote:
> 
> The only thing about lightening is it is unpredictable.
> 
> Lightening introduces voltage into your rigs through two methods; Conduction and induction.  I think most of us have seen the statement that a typical lightening strike a mile away can induce as much a one thousand volts per meter of conductor.
> 
> A strike to your tower is one whale of a lot closer, So, it can induce a lot more than a thousand volts per meter into your house wiring.  That's electrical wiring, telephone wiring, Internet wiring, interconnecting wires between equipment.  IOW any conductors.
> 
> A strike to the tower will follow ALL conductors from the tower. The pulse is divided between all grounding that is connected to the tower.  NORMALLY a good grounding network will reduce conducted voltages as you move away from the tower.  Coax with the shield grounded at the base of the tower, benefits from this same grounding network.
> 
> If the rig is also connected to that grounding "system" there will be some fraction of the original pulse that went into the ground. At the same time, you have induced voltage in ALL house wiring that is connected to the rig(s).  This is NOT DC voltages, but rather a "ringing AC voltage that peaks somewhere around 1 KHz.
> Because of the different routes the voltage takes, the peaks are unlikely to reach the rigs at the same time, meaning the voltage differences may be very large.  A common point ground for all wiring located near the rigs can be helpful and certainly is a good idea (It is recommended), but still offers no 100% guarantee.
> 
> It must be emphasized that NO grounding system offers 100% protection because you have some finite voltage left after all the grounding that depends on the strength of the strike, the conductivity of the earth in which the grounding rods are driven along with the number of ground rods.  NORMALLY as you add to a well designed ground system, the better the protection. BUT you quickly run into diminishing returns where it costs a lot to get even a little more protection
> 
> "The best protection", although not usually practical is to disconnect all wires into the rigs and at the inside of the common point ground which leaves all lines coming in, grounded at that point.
> NEVER disconnect the coax at the rig(s) and leave it/them laying on the floor.  That's worse than Ben Francklin's experiment and very dangerous. They need to be waterproofed and thrown outside.
> 
> Hmmm  Typed this the middle of the afternoon. Brought the monitor up and it's still here.
> 
> 73
> 
> Roger (K8RI)
> 
> On 7/20/2015 1:41 PM, Kent Olsen wrote:
>> Hi all
>> 
>> I have seen the  video on the kf7p.com website about his great looking coax
>> entrance panels that I am planning on buying for my tower.
>> https://www.youtube.com/watch?v=in8x8juZTj8
>> 
>> 
>> Last night we had a thunder storm go over head and it got me thinking. In
>> the video Chris explains about the different connections. The connections I
>> will be referring to are the copper strap from the tower which is grounded
>> through some ground rods and the copper braid from your equipment to the
>> box. Last night  I disconnected my coax from my radio and waited for the
>> storm to pass. If I were to connect the braid to my equipment and my tower
>> were struck by lightning would the energy from the strike go through the
>> strap  to the box through the braid into my equipment in the shack causing
>> damage? Would the ground rod or rods dissipate enough energy to save the
>> equipment?
>> 
>> Thanks
>> 73
>> Kent
>> NC6B
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> 
> -- 
> 
> 73
> 
> Roger (K8RI)
> 
> 
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