[time-nuts] lightening protection of a GPSDO system / optical isolated distribution amp

[Bob Camp]

Hi

Ok, here’s the full and proper answer to the question. Anything less is simply not adequate:

1) Lay down some ground cables, say a few thousand of them. Run them out at least 1/4 mile in each direction from your structure. Make sure they are at least 00 gauge and buried 10 feet deep.

2) At the perimeter (20’ past the walls) of the structure put down an underground aluminum plate at least 1” thick. Extend it  at least 10 feet under the structure. Bond all the ground cables to the plate. 

3) Route all cables, wires, and pipes  into and out of the structure to a single point below ground level. 

4) Bond all cables, wires, and pipes  to the plate at that single point and protect them to the plate with at least six properly rated protection devices in series. 

5) Extend the plate up to enclose the structure. Make sure it does not touch the walls or roof at any point. Nothing from the structure should be outside the plate. There always should be a 10’ air gap. 

6) Make sure that all joints in the plate are properly bonded to each other. Holes and openings are to be avoided. 

7) If EMP from nuclear attack is a major concern, add about 3/8” of steel to the aluminum plate. Make sure all openings are fully covered in the event of nuclear attack. 

8) Put up the usual towers at each corner of the plate, and 20’ beyond the edges of the plate. Independently ground each tower. Run cables between the towers to screen the top and sides of the plate. Tie the tower bases together with multiple 00 cables, all isolated from the ground cables in step 1.  At all points above ground the cable / tower screen should have an air gap of 20’ to the plate. 

Congratulations .. you are now fully protected against lightning ….

You can be sure that your basement timing system will be protected against disruption from lightning to the  99.9999999999% ( 1 ppt ) level. None of your $150 GPS based timing boxes will be damaged. Should you properly and fully implement this system and have a problem from a lightning hit, I’ll personally replace any $150 box that is proven to be damaged by lightning with a similar box from my collection. I also will re-set your local clock against my wrist watch at no extra charge. This is about timing after all :)  Yes, you can paint the structure any color the rest of the family finds pleasing. We would not want our *hobby* to impact them too much. 

Bob

> On Dec 7, 2014, at 7:39 AM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> 
> 
> 
> On 11/27/2014 01:10 AM, Jim Lux wrote:
>> On 11/26/14, 2:54 PM, Hal Murray wrote:
>>> 
>>> albertson.chris at gmail.com said:
>>>> The ground rod needs to be bonded to the rest of the building ground
>>>> system.
>>> 
>>> How do I do that effectively if the power goes in the front of the
>>> building
>>> and the antenna is on the back?
>>> 
>> 
>> AWG 6 wire with no breaks or splices between the two.
>> 
>> The goal of bonding all the grounding systems together is not for
>> transient suppression.  It's to make sure that there's no DC or line
>> frequency potential difference between "electrical safety ground" at
>> various places in the building.
>> 
>> The background on the whole grounding/bonding requirement is more about
>> safety when a power carrying conductor, either inside equipment or
>> overhead, touches something that people might touch. And, to a lesser
>> extent to ensure that if there's an internal short, that the breaker or
>> fuse will trip.
>> 
>> NEC requirements for grounding and bonding aren't there for transient
>> suppression.
>> 
>> A copy of IEEE 1100 (the Emerald Book) is good reading for the whole
>> bonding and equipotential planes, etc.  (unfortunately not free from IEEE).
>> 
>> A good book on transient protection is Ronald Standler's book
>> "protection of electronic circuits from overvoltages"
>> Something like $20 from Dover...
> 
> Do use the ITU-T K-series as a reference, it's a great starting point and they are there for free download. The ITU-T K.27 explains grounding in a station, and that could be interesting food for though in many cases, where people try to motivate Isolated Bonding Network while Mesh Bonding Network might be better in the end. K.40 may be inspiring. K.97 a special case which is partly relevant here.
> 
> Cheers,
> Magnus
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