[TowerTalk] braid and high current

[Nick Pair]

Hello all,
   
  The first problem with braid is that the stuff forms a coating of copper oxide around each strand that is nonconductive. This coating makes each wire like a individual conductor with a resistance according to its gage. Now think of the flexing due to vibration, heat cycling, or any other thing which will cause the strands to rub against each other thus breaking the copper oxide surface. The crossover points of the braid will be alternatively be conducting and then reoxidizing to nonconducting state. This makes all the strands at different resistances which when the 20,000 to 200,000 amp surge hits them will cause some of them to take more of the current than others and vaporize. An avalanche effect occurs and you have meltdown and arcs.
  Second we have the idea that all the current will travel on surface with the skin effect. This is true for normal current amounts but at the current levels of lightning there are not enough free electrons at accommodate the current flow and the conductor depth comes into account. If not enough depth is available the current has to flow outside of the conductor in a arc as there is no where for all those electrons to go.
   
  The use of braided strapping to protect ammunition was to prevent a static discharge from detonating the charges not the high current of lightning. In the workers minds they thought it was for lightning but all you can do with lightning is shunt the current, not stop flow. Even if you shunt 99% of current there is enough voltage to arc at even micro amps which is enough to make fireworks out of your munitions. The only safe place was inside of conductive box with lid closed. (i.e. ammo boxes, metal lined bunkers, etc.)
   
  That leaves us with either large stranded (each strand #12 or larger)  or solid conductors. Even solid has enough flex to allow a fold-over to work if you disconnect(or never use ) the ground opposite the hinge.
   
  Save your braid for your indoor station ground applications.
   
  73
  Nick
  WB7PEK

 		
---------------------------------
How low will we go? Check out Yahoo! Messenger’s low  PC-to-Phone call rates.