[TowerTalk] Ground Rods

[William Sheh]

During a lightning strike whether direct or induced, two main areas must be
addressed to ensure the safety of personnel and equipment.

A ) Current
Lightning Strikes carry a lot of current. 25kA-50kA is very common. High
current traveling through any medium (soil, metal, humans etc..) poses
significant risk of creating large electrical potentials (voltage) and can
induce current flows in near by metallic objects.

B) High Voltage
The extremely high voltages of lightning can cause severe and catastrophic
damage because of the tremendous arcs that can result because of loose
connections or high impedance in the dissipation path. Once an arc occurs,
the temperatures at the arcing locations will instantaneously rise well
beyond the melting or boiling point of the metal (copper, steel, aluminum
etc.). The arcing is what causes the major damage, not the voltage.

That is why everything needs to be bonded together outside the equipment
house, forming a large equip-potential grounding system. This minimize any
unwanted potential differences and present any lighting current within the
system multiple paths into earth instead of  through any piece of equipment.

Will Sheh
ATI Tectoniks


> Does it really matter to a multi-million volt lightning strike whether
> the ground is 300 ohms or five?  The difference would seem to be
> inconsequential.
> 
> This reminds me of the school of thought that says the connection to
> your ground rods must be tight.  As if lightning, having traveled
> thousands of feet through the air, is going to be stopped by a gap of a
> few thousands of an inch.
> 
> --
> Bill, W6WRT