LLigetfa
join:2006-05-15
Fort Frances, ON
kudos:1 | I could use some help with lightning/surge protection I have an existing truck scales operation that is getting outfitted with 8 digital cameras as an automation for manless operation. As we move toward JIT (Just In Time delivery) there is a great emphasis on hight availability so I have to built this with uptime in mind. Since this is also a cost saving measure (manless), I don't have a big budget for this.
I wasn't involved in the preliminary design. At the 11th hour, I was dragged in to provide two things; Network and UPS.
This site is prone to damage from lightning strikes and over the years it has taken a few hits. To mitigate, they had years ago erected 5 poles with air terminals and a cable strung aerially around them in a circle. I haven't a clue what is in the ground.
The new cameras are to be mounted on new poles and wired aerially (no trenching, no conduit) to the shack. The contractor spec'd Outdoor CAT5 and I think separate 24V DC for power, both lashed to a messenger. When I asked the contractor what is spec'd for lightning/surge protection, I got a dumb look followed by the words "you guys didn't ask for that".
I wonder how the grounding should be handled on these poles. I presume an air terminal on every pole with the camera enclosure and messenger bonded at the top of the poles. Should there be a ground wire running down every pole to a rod in the ground? The area is paved over and I don't think they want to rip up asphalt.
I insisted on upgrading the CAT5 and spec'd the outdoor rodent resist stuff. I presume the shielding on the CAT5 should only be grounded at one end, not both and assume the building end is the one to ground, correct?
I also insisted on having entrance protection on all lines that penetrate the building. It is a metal building with a low pitched roof and lots of windows. I'm looking for suggestions on what to spec for; the CAT5, the 24V power, the 120/240V power, and telco lines.
I figure the 120/240 mains should have protection in the breaker panel. I've seen two different styles; one that occupies a breaker slot and the other that hangs off the side of the panel.
Any and all advice appreciated.
Thanks
P.S. This is what is spec'd for camera/enclosure:
SONY SNC-RZ30 Pan Tilt Zoom Network camera
outdoor enclosure and pole mount adapter
SONY SNC-CS3N fixed Network camera and lense
Pelco outdoor enclosure and Pole mount adapter |
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 John GaltForward, MarchPremium
join:2004-09-30
Happy Camp
kudos:3 | What kind of distances are we talking about here (overall and cam poles) and what type of material for the poles? How tall are the "protection" poles and how tall will the cam poles be?
I did upgrade work on 15 truck scales here in Oregon. Some of them were 2,000 feet in length from entrance to exit.
Oh...too bad you got called in at the 11th hour. Don't you just HATE that? Usually the story goes like this...we ran out of money so there is none but we want this cool and groovy system and oh did we mention that things are screwed up and you will have to fix that too but for no extra money or time and we need it all running by next week because we promised that you could do that even though we didn't talk with you first and we have no idea what we are talking about.
Sound familiar?
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LLigetfa
join:2006-05-15
Fort Frances, ON
kudos:1 | Ja, that's just about right. The scope crept and they bought twice as many cameras.{sigh}
I believe all poles will be wood. The existing protection poles are wood, probably around 25 feet tall. Not sure on the camera poles, hopefully a tad shorter. No idea on the placement of the new poles at this juncture.
Since the scales can weigh B trains in one shot (not per axle) and since the parked cab lines up with the shack, I suspect some of the cameras will be set back a fair distance. I have yet to do a site visit with the installer to nail down locations but I wouldn't be surprised if they use some of the protection poles for camera mounts. |
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John GaltForward, MarchPremium
join:2004-09-30
Happy Camp
kudos:3 | Getting back to the topic...I would take a look at how the existing air terminals and down conductors are installed. They may or may not be sufficient. The down conductor should be cadwelded to the ground rod. If it is just clamped on using standard ground clamps then there will be problems in the future. It would be best if they used several rods at each location in a "crows foot" configuration. The spacing between rods should be as far as possible. If it is not possible to do this because of asphalt or similar, a deep driven multi-section rod should be used
The down conductor should be #2 solid at the minimum and should attach to a rated air terminal. The use of copper "tape" is preferred rather than round conductors since it has a very much lower inductance but, given your budget, that is probably out of the question. I would bet that the existing install uses #6 solid copper.
You got what you got...!
All of the messengers should be bonded to the down conductors at each pole using methods that guarantee low resistance and inductance. All of the pole mounted hardware should also be bonded to this down conductor. I would suggest keeping the gear as far from the top as possible consistent with the application and device security.
Polyphaser has many devices specific to the various applications:
»www.polyphaser.com/productdata.a···lass=app
The building and electrical service will need to be appropriately grounded. It should have a ground ring installed. Transient protection should be installed at the service entrance using device conductors as short and straight as possible.
»www.squared.com/us/products/surg···eset.htm
Your comment about grounding the CAT5 at the building is correct. The grounding should be considered as a single point system similar to that found on radio tower sites and all of the grounds should be connected to that point as close as possible.
Just between you and me...expect to lose some or all of the gear as the result a strike. These retrofit jobs with no money to do things right are always a problem. You should warn them in advance that you are doing all that you can given the circumstances, just so they are aware.
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| What is the Earth like in your area? Is it very conductive? |
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LLigetfa
join:2006-05-15
Fort Frances, ON
kudos:1 | I will know for sure when they auger for the poles. I suspect it is clay but it is close to the river so there may be inclusions of gravel. |
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1 edit | If it is crap, you could install chemical rods.
»www.harger.com/products/sub2inde···subid=39
We use them where the ground is poor. They are not cheap, but I suspect after a hit and you loose gear, they'd be able to afford anything....
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"No job is so important, and no service is so urgent that we cannot take the time to do it safely."
-- AT&T
--Safety One Tower Rescue Certified |
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lutfulPremium
join:2005-06-16
Ottawa, ON Reviews:
 ·TekSavvy DSL
1 edit | reply to LLigetfa
BTW remote camera will be sacrificed based on the many "conditions" imposed on the pole locations. 
The potential surge on any aerial cable increases with the height above earth at which it enters the building.
So you need to surge protect EVERY metal conductor of the aerial cable including the shield at the building entry point.
Here are some suggestions for the building entry point for the aerial cable:
300V GDT protector from shield grounding clamp to "very real earth" with a short wide copper cable. Any bonding to building safety ground to be done as low as possible above ground.
90V GDT is fine between 24V POS and NEG. Protector ground bonded to shield grounding clamp with short strap.
15V SAD protector for all Ethernet conductors. Protector ground bonded to shield grounding clamp with short strap.
GDT: Gas Discharge Tube
SAD: Silicon Avalanche Device
I see that Polyphaser has a camera-specific application note:
»www.polyphaser.com/NR/rdonlyres/···0097.pdf |
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LLigetfa
join:2006-05-15
Fort Frances, ON
kudos:1 | I went to the scales site yesterday and was shocked by what I saw. I have to wonder how the existing protection system could even work.
The aerial counterpoise has only a single ground point that is 50 yards away in a drainage ditch, in the opposite direction from the shack. There are lights on the poles, just inches away from the counterpoise. I can see no sign of bonding of grounds, except for the teck on the power cables to the lights. No separate ground wires, no ground rods.
Inside, I cannot see any separate ground wire for the main panel unless it is hidden inside the teck. I cannot see any separate ground wires anywhere going to any ground rods. All I see is one #8 or #10 wire from the telco entrance to a 1/2 inch water line.
The installer says he doesn't need to ground anything, that he is under the umbrella of an existing protection system. 
Cripes, what a mess! What the hell did I get myself into? |
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| Thats a pretty custom ground system. |
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