A Short Antenna Story...

[John_Scher 0]

Sunday afternoon in Nairobi, Kenya; a beautiful blue, sunny day...

I load up the car with wife and child and off we go for a drive to the Ngong Hills (Karen Blixen's old farm land). Lovely drive, cruising in the Benz... when low and behold an “A” comes into view. Ignoring wife’s protests I pull over and do my best to estimate its height; probably about 150ft, not really sure though. A couple of hours later we are almost back home so I call up Mark, my Base buddy and ask him to come see; of course he agrees. I drop the family back at home and go pick up Mark and his wife Annette. Mark and I are the jumpers and Annette, god bless her, has always provided ground support. She takes the videos, fantastic stills and makes the most exotic sandwiches. The three of us constitute the total Base community in East Africa.

Within the hour we are driving back to the “A” replete with laser. As we drive nearer to the “A” I ask Mark how high? He replies “about 100ft to 150ft” I think it might still be still be doable even with our limited experience. Either way this little jaunt breaks up a less than exciting Sunday afternoon quite nicely.

We pull up in a side road and note the “A” is situated in several acres of grass land with a not very dense population surrounding it. Mark points out that it will still have to be done at night. With our limited experience this is going to be a challenge in itself. Anyway off we go, through the perimeter bush, across the unkempt grass land. Within minutes we are at the perimeter wall of the “A”. Jeez this thing seems bigger than we thought, or is it? Out comes the laser and… and… and... bingo, it’s over 400ft tall and 360ft to the small cage platform at the top of the ladder. We can’t believe our luck; we’ve got one right on our doorstep, excellent!

To be honest the realisation that this thing is actually doable changes our thoughts completely; scary and exciting but more scary than anything else.

We work our way round the perimeter wall to the wooden gate noting that the longish grass is not at all trodden down or otherwise disturbed. The gate is somewhat rickety and has cobwebs between it and the frame. No one’s been here for some time. There's no lock, just a wooden slat providing a basic latch. Inside the same feelings prevail: un-trodden grass and an apparently derelict structure. There are no antennas, reflectors, radiators or any other transmitting devices on the “A”. "I don't think anyone's been here for ages"

I see, open up and check out an electrical box which is fitted on the base of one of the legs. I have an HND in electrical engineering so no problems in that department. The wiring inside is hanging loose, the fuses are missing and it’s full of cobwebs and dead spiders. In fact the tower has rust all over it, the ground is littered with old electrical supports and other bits of metal; there’s no doubt about it, this “A” is definitely not in use.

There is a small block building situated right under the tower which we will work our way round to in a minute but for now we are overwhelmed and amazed. I climb up onto one of the concrete blocks supporting one of the legs. This leg has the externally mounted, ladder directly above it. I note and discuss with Mark some huge interlincked but not electrically connected flux rings on one of the legs. I assume that these must be part of a lightning protection system however as I am not unfamiliar with lightning protection systems I wonder why there is no direct connection to earth; no problem, I’ll look it up when I get back to the office on Monday.

Mark is standing on the ground at the base of the block and I am about 5 feet above him. We are looking straight up the ladder which has hoops going over it. It looks like an endless tunnel and really, really scary. The ladder starts about six feet above where I’m standing but I’m sure that I will be able to pull myself up if I just reach up over this shroud and ZZZAAAAAPPPPPP! Bluish flash, smell of bacon (burning flesh), fingers are burning; jeans are smoking and a sharp stinging feeling on my calf muscle.

Derelict tower? Yeah right!

I had made direct contact with the tower with my fingers just above a skirt or shroud. The high Voltage, because I was wearing thick rubber soles, travelled from my fingers to my leg; blew a hole in it, burnt a small hole through my jeans and jumped across a four inch air gap onto a piece of metal protruding from the concrete block.

Needless to say we have since read every forum and have studied everything there is to know on "AM" towers. We do have a plan for jumping it but that’s another story.

In the mean time,

Merry Xmas and Happy New Year to all Basers around the world

from

The Kenya Crew.

[TomAiello 25]

Wow. Good to hear that you came through relatively intact.

I think that a lot of us take more or less for granted that we have more experienced jumpers around who've opened some objects that they can take us to, and that we know are fairly straightforward.

You guys are blazing a whole new trail in that part of the world, and that's an experience that most of us can't even approach.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[lifewithoutanet 0]

Quote

You guys are blazing a whole new trail in that part of the world, and that's an experience that most of us can't even approach.

In an area of the world where a large percentage of the population in the bush carry rifles and would likely be suspicious of someone climbing a tower...possibly poachers.

Good on ya. Hope you guys get that all figured out. Have fun.

-C.

[thawk58 0]

Excellent Story......Rock on in Africa......

[grundleson 0]

ha, figure that one out guys!

Dont die!

[JaapSuter 0]

Hey John,

Great story man. Mind if I copy it on into the story section of BASE WIKI with the pictures?

Thanks!

Jaap

[RayLosli 11]

Hey look on the bright-side. The only Positive thing about getting those Electrical Burns is.
They are Cauterized.......
.

[NickDG 23]

>>A Short Antenna Story...<<

That's a Nugget . . .

NickD BASE 194

[base689 0]

> There are no antennas, reflectors, radiators or any other transmitting devices on the “A”. "I don't think anyone's been here for ages"

> ...the tower has rust all over it, the ground is littered with old electrical supports and other bits of metal; there’s no doubt about it, this “A” is definitely not in use

OK, now it comes my opinion, also coming from experience on the "high voltage" environment. That A is (or perhaps, "was") a AM antenna.
AM antenna's have got their structure physically and electrically insulated from ground and they are fed the electrical signal through a ceramic insulator that has got a HV cable running in the center of it.
The point being: HV signal must go directly to the tower (which is physically the antenna) and same tower MUST be insulated from ground.
Now, let's suppose this A is NOT ANY MORE in use, i.e., there is not any more any HV signal feeding it, they removed the "electrical stuff" feeding it. But the structure remains insulated from ground.
From experience, any "significant" piece of metal that is NOT grounded can accumulate electric charge on itself, due to electromagnetic radiation (of any kind) investing it, due to wind "ripping off" electrons off the metallic structure, due to other causes.
Now, the above A is way BIGGER than significant.
IMHO, John have been electrocuted by "accumulated charge" that existed on such a tower.
Yes, the voltage of such accumulated charge was not so high, but the accumulated charge was very huge (just think about how much metal there is over there...).

> I note and discuss with Mark some huge interlincked but not electrically connected flux rings on one of the legs. I assume that these must be part of a lightning protection system however as I am not unfamiliar with lightning protection systems I wonder why there is no direct connection to earth
OK. I think that those flux rings (not physically/electrically touching each other) are a sort of "over charge protection", possibly also for thunders, but (perhaps) mainly for self-protection of too-high-induced-voltage under operation: There is "small distance" between the metallic parts of the two rings. Under "normal operation" under nominal high voltage, nothing (=no discharge) happens; under "abnormal conditions" (extremely high voltage and/or under thunder/lightning) that structure of interlinked rings would cause a discharge that would stop as soon as the extra-voltage has been got rid of.
The above ("low" high voltage but huge electric charge due to self charging of a huge metallic "hanging" (=not connected to ground) structure) would explain the relatively small bodily injures that John went through.
I doubt that John would have hurt so "little" if trying to touch an active 20 kV AM antenna under normal broadcasting operations.
Just my 0.02€.
If John inspects it (=the whole structure) very carefully and discover that there is NO WIRE feeding the A, he can "ground" the same A, but being very careful. Please, try to get advice on how to do it without hurting yourself by high voltage professionals, but a hint can be: get a copper wire well (=very well) connected to ground on end 1, and the end 2 (of same copper wire) sort of tied to a special pole (in high voltage environment is a sort of fiberglass pole, but actually could be a very well dry wooden pole) and with this pole to get the end 2 to touch the A.
Please, stay a few meters away the end of insulated pole carrying the end 2!!!!!!!!!
Yes, there would be a discharge initially, but after that nothing more "charge" to be discharged.
When A is grounded through the end 2 of copper wire, and while trying to have such an end 2 to stick/touch to A itself, you could possibly get a more proper way of grounding it, climbing on base (=lowest part of A) and connect more properly to the metallic structure a copper wire, connecting the other end to a more proper ground/earth.
Please, seek also other advices from experts in high voltage field.

Stay safe out there
Blue Skies and Soft Walls
BASE #689 - base_689AT_NO_123_SPAMyahoo.com

[Scoop 0]

Now that really is openning up a new A. You would be heroes if you could rig something like that up to ground it and keep it then permanently safe to climb/jump

[John_Scher 0]

All,

Thanks for all the help offered and interest shown, we really appreciate it.

We've been back and measured up for a 24ft, all wood, two piece ladder; it's under construction right now. We've also located the owner and will be making some discrete enquiries.

Thanks again guys,

The Kenya Crew

[base689 0]

> We've been back and measured up for a 24ft, all wood, two piece ladder; it's under construction right now...
Please, keep us updated about the opening of your new A.
A further step beyond climbing on your A SAFELY would be to ground it permanently, so that there is not any more need of wooden ladders or similar stuff.
Take care!!! Talk to you soon!!!!

Stay safe out there
Blue Skies and Soft Walls
BASE #689 - base_689AT_NO_123_SPAMyahoo.com

[TomAiello 25]

Quote

A further step beyond climbing on your A SAFELY would be to ground it permanently, so that there is not any more need of wooden ladders or similar stuff.

I'm thinking that the fact they've found the owner may mean the tower is still transmitting. If that's the case, permanently grounding it would definitely not be a good idea.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[base689 0]

> I'm thinking that the fact they've found the owner may mean the tower is still transmitting. If that's the case, permanently grounding it would definitely not be a good idea.
If you read carefully what I wrote above, a pre-action to ground the structure is "to inspect and verify that the A is NOT fed by any live HV cable"!!!!!!!!
The fact that they found the owner does not mean automatically that the tower is transmitting: if A is not any more in use, it could be the case that the owner owns the land where tower stands, and perhaps the tower itself, perhaps he has got few money for the "disturb" caused by the presence of same tower, but it was not economically convenient for anybody to tear the tower down (there are plenty of cases where there are towers no more in use but left standing because pulling them down is NOT convenient).
So, the inspection of "not-being-live" is a MUST, but at the same time I really doubt that if same A were under high voltage feeding John would have been hurt so "little".
O f course I cannot be sure 100% of the above, but it sounds like the bodily damage done by a huge metallic structure self-charged at a "low" high voltage but at a huge charge (=possibility of releasing huge discharge current). I can tell you the cases (I saw them with my eyes) of 100 km long "thin" cable being extruded outer PE sheath WITHOUT having grounded neither ends: as soon as the worker touched one end, long blue sparkles went from cable end to metallic structure nearby: nothing that could kill a man (...perhaps...) but not pleasant at all... In fact, the worked that worked on that shift forgot to ground the "still" end of same cable.
The reason for the metallic part of the cable been charged is the frivtion caused by the application of PE sheath all over the copper shield WITHOUT same copper being grounded. A "hanging" (=insulated from ground) piece is very likely to be charged (due to lots of different reasons), and the bigger the metal is, the higher will be the charge (the charge, NOT the voltage). But it is the charge (and so the discharge current) that could kill you, not directly the "low" voltage.
To make short along story (please do the following EXACTLY in order):
1) verify CAREFULLY that the A is NOT fed by high voltage
2) ground it with a copper wire (only a couple of mm of diameter) keeping the end that is going to touch the structure ia FAR from human body (fiberglass/wooden/dielectric pole) and possibly wear rubber gloves (that reach half forearm).
In case A is live, attempting the grounding as described above would cause only that a lot of current is running temporarily through copper wire, then the dielectric pole holder will drop same pole and discharge will stop.

Stay safe out there
Blue Skies and Soft Walls
BASE #689 - base_689AT_NO_123_SPAMyahoo.com

[460 0]

BASE 689 is absolutely correct. An insulated nontransmitting (dead) tower can build up an enormous and potentially deadly charge from wind flow past the metal. For example, hang a 100 foot long bare cable wire isolated from ground in the outdoors. Before long, it will be build up an enormous charge from wind flow past the metal. You could discharge this with a suitable ground but extreme care must be exercised.

Looks like a death sandwich without the bread - Steve Deadman Morrell, BASE 174