Conclusions, sample equipment, links, and credits
Are the schematics showing "Multiple-Point"
v. "Single-Point Ground" Not really.
The station simply has it's own SPGS that is bonded to all ground rods and
the Service-entrance.
The service mains (utility entrance) ground is the "single point ground system" for your home's wiring. Phone and cable service must also ground at this same entry point.* A radio facility/station has special low impedance ground requirements that home wiring does not. The station, if not located at the AC service entry, must have immediately adjacent to it's equipment center, it's own single point ground system. Lightning arrestors installed at the station must be on this ground panel. All station equipment must use low impedance conductors to individually bond to this station single point ground. This is one place you should use at least 3" wide copper strap! Discard all forms of "braided" cable. Braid is something a girl does to her hair. It is not a good RF ground and it's a terrible conductor for lightning energy.
You may call this a bulkhead, master ground bus, ground window, etc., but it will be the single point at which all bonding in the station connects. And it must be as close to the station equipment as possible! Then, some part of the station grounding system must bond to the home's utility service entrance ground. That is a critical bond, and it is challenging when the station single point ground is a long distance from the service-entry.
Unfortunately, recall that you cannot maintain low impedance by a long run of wire no matter how heavy the wire is. If your station equipment is more than a few feet from the service mains ground rod, the voltage-differences along the bonding conductor will be significant to the massive energy of lightning. This is minimized by choosing the largest surface-area conductor you can get, and installing intermediate ground rods along the path to the utility service entrance ground. The better the bonding, the stronger the ground system gets. This is rephrased below, because it is so often ignored, to the destruction of equipment:
In house-wiring, the typical #12 or #14 ground wire at AC outlets all go to the service panel (where they also bond to the neutral bus), and then to the service entry single point ground rod. Fine for equipment safety, but totally unacceptable for lightning protection. That permits a massive electrical potential between any part of your house wiring and the potential at the service-mains ground rod. Why? Because your house wiring was never designed to handle lightning energy! But, because your house wiring comes into your station equipment, it is therefore critical that we bond the station single point ground system directly to the utility entrance ground! It's a code requirement (when the station ground is separate from the utilities entrance), and yet so often overlooked by amateurs who learn the hard way about GPR damage.
When it's a long distance from the station ground to the service entrance ground, maintaining low impedance along the whole distance is impossible. But you can make a much lower impedance path than your house wiring provides, and that is vital. I used frequent references to earth-ground along the path (lots of ground rods). This prevents violent current equalization from a direct lightning strike (or high EMI and transients from a nearby strike) and the effects of cumulative impedance along the bonding path. It also gives that long path very high current handling ability, and that's good, because the voltage differences caused by lightning will be large. Bonding to the service-entrance ground is vital to controlling Ground Potential Rise (GPR) from damaging equipment.
GPR occurs when a direct or nearby strike raises and saturates the ground potential so highly that current tries to flow up into your station ground and out through utility wires and/or coax feedlines to anywhere that the ground potential is lower. Fast-acting low impedance grounding helps, but current will not choose your house wiring in a GPR situation if you obey the bonding rules with a direct, high-current capable bonding path to the utility mains ground rod. You will have safely provided a much lower impedance path than the telephone, cable and AC wiring can offer. Failure to shield-ground coax at the main station ground rod closest to the station SPGS can encourage the coax to feed GPR backwards through the arrestors to some distant point of the ground system of lower potential.
The goal is to make the entire ground system feel the same (equipotential) to lightning energy. Heavy gage (#2 or #4) solid copper wire and heavy gage wide copper strapping (6") and many ground rods are the tools for the job. This keeps the designed ground paths of such low potential and high current-carrying capacity, that once on board it, lightning will make no diversions on it's way to harmless dissipation into the earth. That's it. There is no more we can do than to make it easy for lightning to go away once it happens.
Air Terminals (Lightning rods) on the roof of a structure are required every
20' of roof-ridge and within 2' of all roof edges for a structure to be protected
from lightning. Grounded and bonded masts fulfill similar protection (with the
20' horizontal limits and a 45 degree downward cone of protection). But if air terminals
are added they must share the same bonding. Metal gutters and flashing must also
be bonded to prevent flashover around the structure. Buy, borrow, or
check-out the NEC-70, NFPA-780 and books on grounding. All this information,
taken as a whole, provides solid protection for personnel and equipment safety.
* If
you discover that any utility service (cable, phone, etc) is not bonded
to the same single point ground rod (normally found very close to your electric
meter) call the offending utility right away, or if you are qualified,
fix it yourself.
Coax lightning arrestors, shield grounding,
wire-to-ground-rod clamp, copper strap
Gas-tube only. Effective, but...
Multi-mode-suppression, multi-strike. My choice.
Not the most efficient. To ground
your cable
Wire-to-rod
clamp
6" copper strapping
shield, carefully cut/peel outer insulation
and #2
or #4 fits here is
minimum for
wrap copper- foil or use a commercial
shield
Use 5/8" Rod only
connecting to ground.
ground that clamps on exposed outer shield.
Links to Lightning Protection Information:
http://www.rbs2.com/fire.htm#anchor777777
Fire Hazards of Surge Suppressors
http://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/Bonding-Not-Grounding~20040426.php
Short discussion of why common bonding is more important than
grounding. In other words, why bonding everything is more important than
fretting over miniscule ohms of resistance in ground rod references.
http://www.harger.com/ The BEST source of Station Grounding supplies.
http://www.lightningsafety.com/
http://www.arraysolutions.com/Products/ice/index.html
Major dealer for Industrial Communications Engineering (best coax lightning
arrestors)
http://www.nexteklightning.com/index.html
http://www.zerosurge.com/HTML/mode2.html
Good explanation of why Mode-2 (common mode) protection is wrong for
interior surge protection.
http://www.elec-toolbox.com/usefulinfo/lightprot.htm
http://www.packetradio.com/grounds.htm
http://www.astrosurf.com/lombry/qsl-lightning-protection.htm
http://www.glenmartin.com/catalog/lightning.htm
Good examples, but Home Depot & Lowe's carry almost the same grounding
accessories.
If you do decide on Air Terminals, there are new studies that prove Ben Franklin
wrong about the pointed tips...it took 230 years to discover that blunt-tip
lightning rods are much more efficient at delivering lightning bolts to ground.
http://www.lightningstorm.com/tux/jsp/login/index.jsp
Free lightning detection (30min delay on the half hour and hour). Determine
lightning activity in your area.
Credits:
Many thanks to the following Stations and Engineers whose assistance has been invaluable:
KB4CVN, WA4HHG, KB5WZI, K8RI, and:
John M. Tobias, PhD, PE
Principal Consulting Engineer
ElectroQuest, LLC,
http://www.electroquest-llc.com/
Bruce Carpenter Consulting, LLC
P.O. Box 653, Hanover, Md. 21076-0653
http://www.bruce-carpenter-consulting.com/
George Peterson
Transtector Systems
(a Smith company w/ PolyPhaser, and my TVSS systems
provider)
Sr. Gov. Account Manager /Fire & Security
GSA # 07F-5133A
1-208-762-6124
fax 1-208-762-6133
1-800-882-9110 ext 6124
gpeterson@transtector.com
http://www.transtector.com
Joe Nocella, Director of Sales
Zero Surge
(specializing in Normal-mode surge suppression)
http://www.zerosurge.com/
jnocella@ZeroSurge.com |
800-996-6696 Voice | 908-996-7773 Fax
Steve Dawkins, V. Pres.
Auxiliary Power & Control Systems, Inc. (my
power-quality & TVSS installers)
Specializing in Standby and Critical Power Systems
4982 Cleveland St. Virginia Beach, VA 23462
757-497-9169
Index of this Station Grounding Website:
1. Common
misconceptions about lightning and grounding
Explains the differences between direct-strike
protection and surge protection, overall topic coverage.
2.
Basics of lightning,
explaining voltage gradients, common v. normal mode
Graphic and detail of some forces
and effects of lightning; when ground becomes a high-voltage place, etc.
3. Aspects,
components, and damages from lightning
A little science of how nasty this stuff
really is; the raw power and destructive forces of lightning.
4. What
keeps lightning from destroying stuff?
How equipment protection begins and ends
with bonding. If there was a single most important point, this is it.
5. External
Grounds, a better place for lightning
The place where down conductors, coax
lightning arrestors, RF grounding and ground rods meet.
6. Inductance:
why grounding (alone) is never good enough
Why lightning is always able to find
someplace else it would rather be, and without proper grounding and
bonding, it will always get there.
7. Schematics
of USCG Auxiliary Station Oceana Radio
As-built dwgs of the lightning protection
system; RF and lightning ground, coax arrestors, single point ground
system, and details of the Normal-mode surge protection from AC entrance to
station load center, to equipment.
8. Final
conclusions, samples, links, and credits
The end. We never
covered protection for computers, modems, UPS's or generators. But you can apply
what is described here to everything else. Learn more about this and
operate safely. Good luck.
Jack