lutfulPremium
join:2005-06-16
Ottawa, ON Reviews:
 ·TekSavvy DSL
2 edits | Best practice generalized from Motorola/Alvarion docs Our forum keeps having contentious debates on proper method of "grounding and bonding" outdoor WISP equipment and protecting customer homes.
I annotated a few diagrams from various Motorola and Alvarion installation guides and list a whole bunch of relevant threads with lots of opinions. 
some recent debates:
»[Bus. Ops] CPE grounding 'Poll'
»Proper Grounding Techniques for CPE's, AP's and Antennas?
»[Tech Ops] Grounding question for the experienced members
some older threads (2007+ )
»Bonding ground to building ground
»Diagram of proper grounding for integrated CPEs
»I could use some help with lightning/surge protection
»POE and lightning
»How to ground radios and sectors
»grounding gurus? comments please (pics attached)
»[Equipment] Interesting grounding situation
some guidance documents:
»ARRL and Polyphaser lightning protection links
»Polyphaser Document - SPD Technologies
»Grounding and Bonding. More than you will ever want to know.
some damage reports:
»Spring time
»lightning damage..
»Lightening-Direct hit
»Is it just me?
»Damaged xr2? |
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WHT
join:2010-03-26
kudos:3 | 1) I noticed in your drawing annotation in red, "This separation is for avoiding flash-over fire risk", that's going to be hard to do when the #16 (sixteen) gauge wire is stapled to the wood frame of the house.
2) We don't use any station protectors where the ethernet cables enters the house as its not required for our installations.
3) While we could certainly installed a several thousand dollars Polyphaser ground system at each subscriber's home, its not cost effective to protect our radio.
4) The NFPA's NEC recommendations are written for fire safety, not protecting delicate electronic equipment. That's what home owner's insurance is for. |
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WHT
join:2010-03-26
kudos:3 | reply to lutful
Furthermore....
5) The "Andrew Grounding Assembly to Tower" should attach to the vertical portion of the ethernt cable before it makes a sharp turn to go horizontal.
6) The Avarion drawing a) omits tying the two ground rods to each other, and b) omits (or at least doesn't *clearly* show it) bonding the down conductors to the AC utility ground rod. |
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 seagreenPremium,Mod
join:2001-05-14
out there | reply to lutful
My warning in the "Lightning damage pics" thread extends to this thread as well. If the squabbling starts up again there will be consequences for ALL participants. |
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lutfulPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
| reply to WHT
said by WHT:"This separation is for avoiding flash-over fire risk", that's going to be hard to do when the #16 (sixteen) gauge wire is stapled to the wood frame of the house. FYI just the shielding of most outdoor cables ( coax or STP) can carry much more current due to larger metal surface and their outer insulation provides some protection against flash-over.
Meanwhile 2.4Ghz/6Ghz Coax and 10/100 PoE surge protectors have come down in price due to large WISP market.
Above "minimal" setup will provide reasonable lightning surge protection of customer premise. The main point is that all surge protector lugs need to be bonded together and to "real ground" outside the home as low as possible.
Finally any bonding to electrical ground for local code compliance should also be done outdoors, preferably below ground level. |
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WHT
join:2010-03-26
kudos:3
2 edits | said by lutful:FYI just the shielding of most outdoor cables ( coax or STP) can carry much more current due to larger metal surface and their outer insulation provides some protection against flash-over. The drawing is referring to a ground wire, so I don't know how your answer about ethernet cable and coax comes into the picture. And the #16 gauge wire we use isn't insulated anyway.
said by lutful:Meanwhile 2.4Ghz/6Ghz Coax and 10/100 PoE surge protectors have come down in price due to large WISP market. That may be, at $30 to $40, but we still don't need to install them.Edited to add...Those are prices for outdoor protectors. Though I don't know if the cost of indoor units placed in a several dollar weatherproof box would be less expensive.
said by lutful:Finally any bonding to electrical ground for local code compliance should also be done outdoors, preferably below ground level. That may be a good idea, but certainly not required for NEC building code compliance. NEC Part 800, et al, allows it to be inside the building structure. |
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lutfulPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
| said by WHT:I don't know how your answer about ethernet cable and coax comes into the picture. I was proposing absolute minimum lightning surge protection of only the customer premise using large circular mil surface of typical outdoor cable shields.
However I want to emphasize the "best practice" suggested by 2 very reputable companies should be followed by WISPs for sufficient lightning protection.
said by WHT:the #16 gauge wire we use isn't insulated anyway ... may be a good idea, but certainly not required for NEC building code compliance. NEC Part 800, et al, allows it to be inside the building structure Perhaps NEC suggests minimum #6 grounding wire from rooftop antenna? Anyway you could draw a simple sketch of your current practice and explain to WISPs how it provides sufficient protection from a lightning surge.
You will find justifiable criticism of NEC requirements expressed by »gpr-expert.com/cell-site2.htm and other professionals engaged in lightning protection system design. Fortunately NEC does allow WISPs to do implement more protection than they mandate. |
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WHT
join:2010-03-26
kudos:3 | said by WHT:I don't know how your answer about ethernet cable and coax comes into the picture. I was referring to the ground wire, not cable shields, where you annotated separation for fire safety.
said by WHT:Perhaps NEC suggests minimum #6 grounding wire from rooftop antenna? I never heard of the NEC suggesting #6 wire for the down conductor from the roof top. Do you have an Article number for that so I can look it over? Nevertheless, we get by with #18 gauge just fine. Would there be a building code problem with that? |
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lutfulPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
| said by WHT:I never heard of the NEC suggesting #6 wire for the down conductor from the roof top. Do you have an Article number for that so I can look it over? Nevertheless, we get by with #18 gauge just fine. Would there be a building code problem with that? There may not be a "building code" problem with #18 but even #6 is inadequate for diverting lightning surge to ground. You can check many references on-line about surge current carrying ability for various circular mils. |
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 John GaltForward, MarchPremium
join:2004-09-30
Happy Camp
kudos:3 | reply to lutful
All that is required is compliance with the NEC and not one single thing more.
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Remember, Tuesday is Soylent Green Day.
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WHT
join:2010-03-26
kudos:3
2 edits | reply to lutful
said by lutful:said by WHT:I never heard of the NEC suggesting #6 wire for the down conductor from the roof top. Do you have an Article number for that so I can look it over? Nevertheless, we get by with #18 gauge just fine. Would there be a building code problem with that? There may not be a "building code" problem with #18 but even #6 is inadequate for diverting lightning surge to ground. You can check many references on-line about surge current carrying ability for various circular mils. I never asked if it was adequate for diverting a lightning surge.
I never asked if #18 was adequate for diverting a lightning surge. (edited to be specific)
I asked if you had a NEC reference that said I have to use #6 wire for the down conductor.
And there isn't any "may" be a problem with building codes, there isn't. Period.
(edited to add...again)
It is impossible to achieve adequate separation of my ground wire if I staple it to the wood frame of the house? Is it a requirement of any sort? |
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lutfulPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
1 edit | said by WHT:I asked if you had a NEC reference that said I have to use #6 wire for the down conductor This was not supposed to become an NEC discussion. Since NEC docs are not freely available, let me offer interpretation by Mike Holt who is well respected in our forum and wrote this article ( »ecmweb.com/nec/code-basics/elect···evision/ ) and many others on NEC compliant grounding/bonding. If some WISP installed CPE antenna according to above sketch for satellite dish, I guess it would be OK under most circumstances.
Of course every USA WISPs could implement only the "absolute minimum" antenna grounding requirement in NFPA 70 (aka NEC) but NFPA 780 is specific to lightning surge protection. Meanwhile IEC recommendations apply in many countries outside the USA. |
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WHT
join:2010-03-26
kudos:3 | 1) The NEC 2005 is most certainly freely available from NFPA website.
2) I'll go with what the NEC officially says instead of an interpretation or guess.
quote:
810.21 (H) Size The grounding conductor shall not be smaller than 10 AWG copper, 8 AWG aluminum, or 17 AWG copper-clad steel or bronze.
3) The NEC does not define "absolute minimum", therefore the way I am doing it satisfies all the NEC recommendations and municipal codes.
Sorry if I wasted your time. |
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 warwick
join:2009-06-05
Hollywood, FL | reply to lutful
This Jargon again?! .... pshh. 
I assume most here could not care less about NEC/UL/NFPA specs...this forum section is (again I assume) dedicated to the discussion of wireless related info. Ya no, dbi, dbm antenna theory ... those things.
That is not to say grounding is not an imperative topic... its just a topic better reserved for another forum section.
If its one thing I've learned over the years, its that if Lightning wants it, it'll get it...
to think the scientists haven't repletely understood what causes lightning and you have some that will argue, well this way is better than this, oh no wait well I have 40 degrees alongside a phd mines must be a better solution.
Calm down... |
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WHT
join:2010-03-26
kudos:3 | The forum encompass all aspects of running a WISP, including keeping the customer installation cost as low as possible (and still meet whatever goal you have). Customer installations includes meeting applicable grounding specifications. Failing to meet NEC recommendations increases the liability as lack of appropriate grounding is the first thing the insurance companies will deny compensation for.
said by john galt :
All that is required is compliance with the NEC and not one single thing more. |
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| reply to lutful
I use a simple rule of thumb for grounding. If the grounding system is more expensive than the equipment it protects, skip it. |
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lutfulPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
| reply to warwick
said by warwick:I assume most here could not care less about NEC/UL/NFPA specs... But WISPs do care about proper grounding/bonding for both safety and also lightning protection judging by the many discussions we had since 2005 when I joined this forum. You could check my initial posts in this and a few recent threads ... I rarely mentioned NEC/NFPA/UL before someone else brought it into a discussion.
FYI a very dedicated group of Ph.D EE researchers investigate why/how lightning does what it does - I only track their publications due to my personal interest and involvement in robust lightning protection systems. |
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John GaltForward, MarchPremium
join:2004-09-30
Happy Camp
kudos:3 | reply to warwick
said by warwick:That is not to say grounding is not an imperative topic... its just a topic better reserved for another forum section. Feel free to start your own thread on any other topic you choose...
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Remember, Tuesday is Soylent Green Day.
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WHT
join:2010-03-26
kudos:3 | "Meeting NEC Compliance" thread title comes to mind, as the threads so far keep hammering on protection, rather than simple compliance. |
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lutfulPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
| said by WHT:"Meeting NEC Compliance" thread title comes to mind I think something like "NEC compliance for outdoor installations in USA" would be more appropriate when you are ready to post that thread. Please mention code requirements for CPE mounted on a rooftop pole/mast and also small tower/mast near the home.
said by WHT:threads so far keep hammering on protection, rather than simple compliance. This is not an April fools' joke - I took this photo back in 2002 near an overseas NOC.
You will find thousands of VHF/UHF omni setups like this in South Asia. The coax shield is grounded near the building entry point for "simple compliance" with local safety codes and bamboo mast is suprisingly durable and amazingly eco-friendly.
By contrast, the ISP folks have literally "hammered out" some rebars embedded in rooftop concrete to provide sufficient grounding through the building structure to provide 100% protection for critical VSAT links to the outside world.
Curiously this particular omni antenna on bamboo mast has survived hundreds of close lightning strikes since then ... because it is located inside the building's lightning protection zone. Exposed setups like this tend to "obliterate" long before the next blue moon.  |
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