[RFI] Daisy-chain grounding [was DigiKeyer II]

Dale svetanoff at earthlink.net
Sat Dec 21 12:23:07 EST 2013


Please see my inserted comments below.

73, Dale

-----Original Message-----
>From: "Anthony (N2KI)" <n2ki.ham at gmail.com>
>Sent: Dec 20, 2013 4:14 PM
>To: rfi at contesting.com
>Subject: Re: [RFI] Daisy-chain grounding [was DigiKeyer II]
>Thanks for the links to the r-56. Its always informative when reading about
>grounding your station.  I have a perimeter ground here.  There is #6 bare
>copper wire that starts at the ground rod outside the shack and is one
>continuous run that has an 8 foot ground rod placed every 16 feet, picks up
>every ground rod on each tower, continues and picks up the electrical
>service ground rod and then terminates back where it began,  Again, all in
>one run of wire with a ground rod every 16 feet.  All the equipment
>(including computers) here is bonded to a buss bar on the back of the desk
>and that buss is in turn bonded to the perimeter ground through a
>NEMA enclosure with all the lightning arrestors and copper buss.(via 1 inch
>braid from the equipment buss to the lightning arrestor buss).  Also, the
>coax shields are grounded at the top and bottom of the tower with the MOV
>at the base.  I think somewhere it says it is supposed to be done every so
>many feet down the tower also but I did not do that.
- - - - - - - - - - -

Your setup is nearly identical to mine. The main difference is that I had to integrate 3 towers into the grounding scheme.  One caveat: you mention 1" braid between the buss bar and lightning arrestor bus.  Is that braid exposed to the weather?  If so, you may wish to inspect it for corrosion.  See my comments below and in an earlier posting about that.
- - - - - - - - - - -   
>I had a direct lightning strike on tower number one and only
>lost equipment that was connect to my computer via USB.  After looking at
>the setup, I realized that I did not have any protection on my network CAT6
> that runs through the entire house.  Somehow the charge got onto the
>network and only affected 1 computer and anything connected via a USB.  I
>found some surge protection to add to the network that APC makes.  I add
>those in strategic locations (I hope) on the network.
>My wife was home and watching TV when the strike occurred. After
>she pried herself off the ceiling, she looked outside to see
>my vertical V/U antenna blown to smithereens. When I queried here about
>what had happened she described that when the strike occurred, all
>the appliances when off and then all came back on after a couple of
>seconds.  Not one piece of anything other than what was connected to the
>computer was blown.  So having a single point ground system is definitely a
>good thing.  Its not 100%, but I take the 99%.
- - - - - - - - - - - - - - 

To minimize recurrence of a similar situation should you get a similar strike, I'd suggest two things: 1) Get a whole-house surge protector installed at your main power entrance panel.  If possible, get the kind that not only protect the main AC feeds , but which also have built-in protectors for CATV feeds and telephone or data lines.  2) Get supplemental surge protectors for EVERY outlet that feeds sensitive equipment (radios, TV, computers, refrigerators (yes!), and so forth.  The protection warranty on my whole house surge protector (Square D) is null and void unless such devices are used downstream at the various loads.  (I have previously posted the reasons for that.)  

I have to say that USB cables are a story of their own.  I bought a laser printer earlier this year and connected it to the computer via USB.  All was well until a strong thunderstorm struck in mid-June.  There was a big cloud-to-cloud strike almost directly overhead of the house.  I didn't thing much about it until I went to use the printer the next day.  The printer's boot sequence failed at RAM check.  I soon learned that my 3 month old printer was "toast", but did get a new one under warranty at no cost to me.  Other equipment connected via USB was fine - only the printer died.  No power was applied at the time (the computer and printer get power from a surge-protected UPS that was off at the time).
- - - - - - - - - - - -                   
>So I guess my question is do I change out the 1 inch braid to #6 that
>connects the buss bar to the perimeter ground?  All the equipment has braid
>pigtails to the buss bar.  Suggestions?
- - - - - - - - - - - 

Yes, if the connection goes outdoors, I strongly suggest the use of #6 versus braid.
- - - - - - - - - - - -
>Anthony (N2KI)
>On Fri, Dec 20, 2013 at 3:42 PM, <donovanf at starpower.net> wrote:
>> Note that the Motorola Standards and Guidelines for Communications Sites
>> (page 8-3) states that:
>> "Braided wire shall not be used..."
>> 73
>> Frank
>> W3LPL
>> ----- Original Message -----
>> From: "EDDIE J EDWARDS" <eedwards at oppd.com>
>> To: "jim at audiosystemsgroup.com" <jim at audiosystemsgroup.com>,
>> rfi at contesting.com
>> Sent: Friday, December 20, 2013 6:06:27 PM
>> Subject: Re: [RFI] Daisy-chain grounding [was DigiKeyer II]
>> Jim,
>> Actually, you are correct in the sense that the R-56 grounding guidelines
>> are not based on circuit board designs, but they are based on real world
>> problems and experience on lightning protection at commercial transmitter
>> comm sites so a different set of "circuit fundamentals" are applied for a
>> different signal source. As they say, one size doesn't always fit all for
>> differing electrical circuits. AC power circuits are based on different
>> fundamentals from RF circuits or from audio circuits depending on the
>> signal used. And RF ground is different from AC safety ground, etc...
>> Motorola expanded their original R56 guidelines from around 50 pages to
>> 518 pages in 2000 in response to repeated equipment failures at radio sites
>> related to poor installation practices when following their old R56
>> booklet. Lightning is not equivalent to a DC circuit or even a more complex
>> signal like an audio or data circuit. Lightning protection, as I understand
>> it, is based on creating a single current path with the lowest possible
>> "impedance" for a lightning strike covering from DC to RF energy.
>> The theory is "daisy-chaining" or series connections that create multiple
>> connections on each device can create impedance "bumps" increasing overall
>> impedance all along the chain. Even if only two wires are connected to the
>> exact same point on a device, it is considered a "multiple-connection",
>> i.e. more than one conductor/wire making contact. Lightning will find the
>> path of least impedance (not least resistance) so these little impedance
>> bumps might cause the lightning path to go somewhere unexpected like
>> through some portion of the devices' circuit boards instead of the desired
>> path. This is especially true if the multiple ground wires are incorrectly
>> connected to multiple locations on the same device leaving a new possible
>> path through the device's circuits instead of around it.
>> Another problem with daisy-chaining in commercial set-ups is what happens
>> when a technician temporarily removes one of the devices in the middle of
>> the daisy-chain for repairs. The result is most of the other devices are
>> left unprotected until the missing device is returned to service. You just
>> cannot predict what service techs will do on a given day, but especially on
>> a Friday! ;-)
>> When Single-Point grounding is done correctly, it will greatly reduce (but
>> not eliminate) the chance of lightning damage to equipment that operates
>> 24-7. Motorola expanded use of single point grounding requirements with
>> Motorola's R-56 in 2000 (updated in 2005) which can be found on-line at
>> this link: (see Chapter 5 section 5.4.1 page 5-33,34 for specific
>> daisy-chain info):
>> http://www.radioandtrunking.com/downloads/motorola/R56_2005_manual.pdf
>> M/A Com (back in 2001) also had or has a shorter 56 page version
>> (ironically numbered), but also requires single-point grounding that meets
>> the National Electric Code (NEC). (See
>> http://www.repeater-builder.com/ge/lbi-library/t4618r3a.pdf see section
>> 1.5.1) (Note: The M/A Com guide still refers to use of an internal comm
>> room "Halo" which has been abandoned by most vendors today.) I believe NEC
>> also forbids multiple wire connections (similar to daisy-chaining) for
>> safety reasons in electrical circuits.
>> All that being said, I'll repeat what I said originally: The typical or
>> simple ham radio station can probably get away with some very short-runs of
>> daisy-chaining (especially on computers) since most hams have
>> human-operated layers of lightning protection such as disconnecting all
>> antennas and grounding all the cables at the entry port during possible
>> thunderstorm periods. If a ham does all that, he reduces his risk of the
>> daisy-chaining having any impact.
>> On the other hand, a multi-multi contest station should probably employ
>> the same single-point grounding standards that the commercial guys do
>> whenever possible. Also, I would not daisy-chain computers and RF devices
>> together, but keep them separate if at all possible. Physical equipment
>> layout to separate RF devices from computers would make this possible. I
>> keep my computers on station left and RF on station right or middle with
>> cable entry from the right.
>> QST has had some good primer articles on lightning protection and
>> grounding for ham shacks: a search for lightning in ARRL's Periodicals
>> Archive found an article in 2002, June & July. I know there are others more
>> recent.
>> 73, de ed -K0iL

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