Outdoor Wireless Installation Lightning Protection

[rigbyorange]

Hello,
Just wondering if anyone has experienced this problem. We have an outdoor wireless installation and everytime there is a thunderstorm, the power supplies on some units are zapped. We have surge protectors and it does not appear that the problem is coming from the outlet. I was wondering if there might be a static buildup around the antennas that is causing this. If so what solutions are recommended for preventing the loss of the ac adapters? There is thankfully no damage to the AP itself.
Thank you.

[spiderbite]

Absolutely!!

The EMF generated in the storm can utilize the antenna as a path and burn up all your gear, your house, and anything else. Doesn't require a direct hit.

www.polyphaser.com makes some good lightning surge arrestors. Look for the gas charged replaceable element kind. Put them on everything with an antenna.

Although it is wierd that the radios lived and the AC adapters died......

[rigbyorange]

spiderbite,
Thanks for the reply. Would running a ground wire from the antenna to the ground do the trick? Do I need to combine this with the lightning protectors as well?

[ConnClark]

rigbyorange,

Well, I wouldn't say its exactly static buildup around the antennas. Surge protectors can't block everything, and the MOVs they use to block spikes eventially wear out. (See here for explaination but I am not endorsing this companies product because I haven't used them http://www.zerosurge.com/HTML/movs.html ). It sounds more like crummy power supplies IMHO. I would recomend finding another type of power supply to try that meets or exceeds the same specs.

Is it just the outdoor units that have the power supplies going out? Is it a POE system? How long is the power cable being run? What is your outdoor unit being mounted to and how is it mounted?

I do recomend you use lightning protection in between your antenna and your AP. Polyphaser is a good company and their web site has lots of information on proper grounding and the physics of lightning protection (READ IT). IMHO gas discharge tubes as a primary protection scheme are overrated, by the time the gas has ionized the damage is done. As a secondary protection layer they make sense though.

Good Luck,

Conn Clark

[spiderbite]

The lightning arrestor must be grounded to the common earth ground. Yes use the arrestor as well...do not just run a ground wire from the antenna and DO NOT make a separate ground. Very bad juju.....

Conn Clark,

So the Gas ones arent that great? I've never seen one "used" so I always understood that because it was replaceable it was " better"...

I have been putting Arrestors near the radio usually inside the building with the AP because it is closer to something to ground to.
Can you use one at the antenna and another at the radio? is this paranoia?

[ConnClark]

spiderbite,

The Gas tubes are not all that great any more. Even polyphasor who owns the patent has pretty much ceased development on new products using them because they can get the same or better results with other methods. With the equipment and systems we sell to customers we have never seen one of the DC blocking lightning arrestors fail, even with multiple strikes. This doesn't mean they won't but we have never seen it.

IMHO, the best thing to do is keep the surge outside the building if possible. If possible I would use a DC blocking lightning arrestor and run it straight to earth ground. This is not always an option depending on how you power your AP and how the AP's power system is designed. Your AP needs to have total DC isolation in the power supply to do this to avoid ground loops.

Doubling up on lightning protection is NOT flat out paranoia. You just need to weigh the monitary cost, odds of it hapening, and loss in performance against the financial hardship, saftey threat, and hassel of system failure. Lightning arrestors do fail from time to time and lightning does strike twice in the same place occasionaly.

As a side note, I have been in a house that was struck by lightning when I was about 12. It was not a pleasent experience. My grand parrents TV antenna was not properly grounded and went straight to the TV. Well after the lightning totaly destroyed the TV it arc to two different outlets. We had quite a large flash and even louder BANG. Everyone in the house looked at me to see if I lit off an M80 or something. I wouldn't light something like that off in the house of course, but thats what everyone first suspected. They then realized that it wasn't me when they noticed the TV no longer was functioning.


To sumerize, plazma inside a building is very very bad.

Conn

[rigbyorange]

Hello,
Our outdoor installation consists of access points mounted in NEMA enclosures on the exterior of the buildings. The APs do not have grounded ac/dc adapters, similar to those provided with linksys or dlink APs. We then have an external 2.4GHz antenna connected to the AP with LMR400 running out of the box to the roof of the building. Some locations have 2 external antennas running to the same AP.

We have not had any lightning strikes, but when there is a lightning storm, the power supplies on some units go bad and need to be replaced. This only happens on the outdoor units. All APs are powered by a 10ft long 18V 1A power supply. This happens even when there is no power surges or brownouts in the rest of the building. Every device on the same electrical circuit as the AP is fine. Only the power supply on the AP is damaged.

Thank you for the posts, but I am still curious as to the best option for this installation. Does this sound like a problem with the surge protectors? I really feel that it has something to do with the electrostatic discharge at the antenna.

Spiderbite, what did you mean about making a seperate ground?
Thanks

[spiderbite]

Rigby,

Please forgive me as I am not an electrician, or a grounding engineer, or even completely understand the concept of grounding.


However, The building has what is called a common earth ground.

My house has a large metal rod pushed in the ground and the electrical panel and every thing in the house that is grounded has a path to this rod...somehow.


If you were to, for convienience's sake, make another ground rod somewhere else for the purpose of grounding antennas that was not connected to the original ground rod, you have created a path for all the energy in a lightning strike to go.


When you are properly grounded all the energy is grounded and the "pressure" of this energy is negated...(I think)

In the other situation, you have inadvertently given that pressure another path (of least resistance) and something similar if not worse than the episode Conn Clark described would certainly occur. This is how people burn thier houses down.

Conn Clark, I would like to take our conversation offline. I'm very interested in your opinion and am curious as to what you think about a particular situation I'm facing...

[davismit]

I take it you are running CAT5 to the outdoor WAP enclosure as well as DC power then a coax cable out from there to the antenna...

'I recently deployed a Proxim Tsunami Quickbridge 20 Wireless bridge and used Transtector ALPU-TSU Lightning suppressors on the CAT5 feed to the antenna units. You can get em at CDW.
CDW Part: 62778 $99.31 each

Put one or two of these between your outside gear and your inside network switch.

The Transtector ALPU-TSUs can also carry Power over Ethernet (PoE.)

One note of caution... if you plan to use PoE you MUST alter the CAT5 wiring as the DC power will be shorted if you use the Transtector as is out of the box. I made some short pigtails to deal with the DC power shorting problem.

No PoE, no problem, just use straight through or a cross over cable as needed.

We have had a couple of really nasty thunderstorms recently and the wireless bridge never skipped a beat.

In the past we have had entire building networks destroyed by lightning strikes making it to the CAT5 wiring in the switch closet. Big mess.

See the attached jpg file for the diagrams of how I did it. At the bottom is a very basic schematic of the whole setup.

Dave

[ConnClark]

Sorry everyone, I got very busy yesterday and couldn't get time to respond.

Rigby,

Your problem is very strange. I don't think 10ft of power cable would pick up strong enough spikes from a general lightning storm to damage a power supply unless lightning struck right next to it. It sounds more like its coming from the AC side and your power supplys are really susceptible to failure from spikes. You might consider filtering technology from people like Zerosurge depending on the cost. I strongly doubt its static. If you really think its static you can run a 10 meg ohm resistor to ground from the unit to eliminate that as a possibility.

I will say that it sounds like you really should seriously consider adding lightning protection. I would also recomend adding a network surge protector to the cat5 run going to the outdoor unit if you use one as davismit suggested.

To anybody that wants to do lightning protection right, I suggest they find some local ham radio operators. They either know or can find an expert really quick and have extensive resources they can point you to.


spiderbite,

I'm not an expert on grounding, installation, or lightning protection. I do design a portion of the equipment we make. I do have an idea of the basic concepts though. If you want to run something by me you can reach me through email clark (at) esteem (dot) com . I may not be able to respond right away as I have to do some work under winDOS (I do my email and most other work under linux).

keep it safe,

Conn Clark

[rigbyorange]

Conn Clark,

Thanks for the response. The reason I think it might be electrostatic build up is because I experienced this same problem last summer. After a few storms, none of which had lightning strikes anywhere near our installation, I purchased some 14 gauge copper wire. I wrapped the wire around the shielding of each antenna and ran it to a common ground. We had several big lightning storms and never lost a single power supply. A year has passed and now I am having the same problem. I have noticed that the copper has corroded a bit over the past year and that could be the problem. I have tried different power supplies and surge protectors and still have the same problem. Probably just need a better grounding scheme. I appreciate all the help in this forum. I am working on a better grounding scheme and will update you on my findings.
Thanks....