Topband: Base Insulators for Verticals

Tom Rauch w8ji at
Sun Sep 10 03:43:43 EDT 2006

> Using three separate insulators, one in each leg of a 
> guyed tower, is about
> the WORST possible approach.  Most insulating material has 
> excellent
> compressive strength, but poor tensile strength.  With 
> three insulators, one
> in each leg, whenever the tower sways, there will be 
> compression on at least
> one insualtor, but tension on at least one other.  Even a 
> guyed tower will
> sway to a  certain extent during heavy winds.  The risk is 
> that one or more
> insualators will crack, or separate from the casting that 
> caps the end of
> the insulator.

I agree 100%, but would also add twisting motion to the 
problem. Towers also tend to twist in the wind. It's very 
important the base be able to rock and slightly twist on 
some form of pivot without doing anything but placing the 
insulator under compression.

It's far better on guyed towers to bring all three legs to a 
single point or a very stiff flat plate and have the tower 
sit on a single pin on top of or below an insulator.

There are cases where multiple insulators are used, such as 
self supporting towers, but the insulators aren't something 
turned from some plastic that doesn't even weather well. The 
insulators I've seen in those towers are also designed to 
stay in compression.

It's one thing with a 30 foot vertical, but when we start 
getting out to a hundred feet it's time to be careful and do 
things the right way.

73 Tom 

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