Topband: What percentage of the length ...

[W0UN -- John Brosnahan]

At 04:06 PM 1/20/2005, you wrote:
>G'day,
>
>| BTW   10% plus two feet is the recommendation of the
>| Lineman's and Cableman's Handbook, 7th edition, by Edwin
>| B. Kurtz and Thomas M. Shoemaker, page 11-3, both in the
>| text and in Table 11-1.
>|
>| Of course it is soil dependent and in rock the depth is significantly
>| less.
>
>Not sure I like that last bit.  What exactly does "significantly less"
>mean?  I've planted a few 28 foot poles and wouldn't consider anything
>less than 4.5 feet depth particularly if I'm going to be swinging about on
>it.  Sods law says when she tips you'll be under it when it hits the
>ground.  I guess if it's in a 3 foot hole pecked into rock it will only
>tip as far as the soft packing allows.  Experience during my time with the
>Post Office, now BT, in the UK suggests that concreting a pole in
>seriously reduces its working life.
>
>Regards,
>
>Mike VP8NO


OK, Mike --

I was just trying to provide the reference to those who needed the info.
And I didn't think that anyone would be going into rock.  But I will
reproduce the table for everyone's benefit.

First off, the text reads "A rule for determining the setting depth in soil
is to take 10% of the height of the pole and add 2 ft, with a minimum of
5 ft.  And this is for poles in a straight line.  If the pole is an angle
point or a corner point it should be set AT LEAST 1/2 ft deeper."

Obviously the depth is a function of load and of soil conditions so
these guidelines are just that, guidelines.  If the soil is unusual
then you need to set the pole deeper and at some point you will need
a soils engineer to sort out the details.

So here is the table for both average soil and rock. It is not MY table
but rather the table in the Handbook for Linemen, based on decades
of experience.   The guidelines for typical poles match the formula for
soil, but the very shortest poles and the tallest poles have obviously had
a fudge factor added.

Pole length     Setting Depth   Setting Depth
in feet                 in Soil                 in Rock

20                      4.5                     3.0
25                      5.0                     3.5
30                      5.5                     3.5
35                      6.0                     4.0
40                      6.0                     4.0
45                      6.5                     4.5
50                      7.0                     4.5
55                      7.5                     5.0
60                      8.0                     5.0
65                      8.5                     6.0
70                      9.0                     6.0
75                      9.5                     6.0
80                      10.0                    6.5
85                      10.5                    7.0
90                      11.0                    7.5
95                      11.0                    7.5
100                     11.0                    7.5
105                     12.0                    8.0
110                     12.0                    8.0
115                     12.0                    8.0
120                     13.0                    8.5
125                     13.0                    8.5
130                     13.0                    8.5
135                     14.0                    9.0

73  -- John  W0UN