Thursday, 1 August 2013

Earthing the mast

Today I decided to connect a protective earth ( ground) to my Versatower.
This mast has been up for 11 years next month and in all that time I have not had a grounding system in place. I've relied on luffing the mast over whenever there is a storm in the area.
After a long chat with G3NYK and G4HUP about this at our weekly coffee get together last Sunday I decided I really had to do something.
Today was the day.



For now I am relying on a single ground rod. I will increase this to 2 or three in the very near future.
What has been the problem up to now is deciding how to connect to the metalwork of the tower. Although the round sections of the lattice would be a convenient place to make a connection, the fact that the mast luffs over means that a long ground lead would be required when new mast was puffed over. That is not a good idea. The ground lead should be as short as possible to ensure that the inductance of the lead is low. The rapid rise time of lightning discharges do not want to encounter a lot of inductive reactance.
I decided to drill a 9mm hole on one of the mast ground post locating 'pegs' and fit an M9 stainless steel bolt that would hold the ground lug on one end of the ground wire. These pegs are the nearest point on the mast to the ground beyond the concrete base of the mast. The locking pin prevents getting too close to the end of the peg, but near enough.
The photo shows two parallel ground wires. This is probably not a good idea and a single, large diameter, or flat, non-braided, ground would be better and will come later.
The ground rod is driven 4 foot into the (soft sand) and the big brass clamp is secured to the ground wire lug with brass M8 stud and nuts.
The black 'gunk' is an RTV sealant to protect the lugs and screws as well as the wire.


Sam



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