Gerald,
Could you point me to the 35kpsi spec? I couldn't find a steel spec on
the Wheatland EMT manufacturer site, or that matter on any other site I
looked at that google turned up re conduit specs.
Here is a section from a Q&A by the Steel Tube Institute re the
controlling ANSI 80.3 standard for electrical conduit
"Rigid conduit is intended for electrical applications, not structural
ones. Its requirements are governed by UL and ANSI specifications, not
by ASTM. The main issue here is that, whereas dimensions may be similar
between the two, rigid conduit is not intended for, is not designed for,
and is not tested for any strength or structural requirements."
So while the yield number and wall thickness in the mast calculator turn
out ok, YMMV. And likely with the thin wall it will deform with boom
and rotator clamps.
Standard schedule 40 water pipe would be a much better choice for
several reasons:
1. the grade steel is specified
2. it is specified to withstand an internal pressure, which is a control
on the seam weld quality
3. it is allowable in structural applications, although used mostly in
larger diameters.
4. hot dip galvanized inside and out
Caveat emptor. Unless it falls down, and your insurance asks about the
engineering and the plaintiffs attorney finds the statement to the
effect "I don't care if it falls down."
Grant KZ1W
On 3/15/2016 12:35 PM, TexasRF--- via TowerTalk wrote:
Google says 1.5" EMT is actually 1.75" OD and .065" wall thickness and
yield strength is 35,000 psi.
Putting these numbers in a mast analysis program and using a 7 sq ft wind
load 24" above top of tower, failure happens at a wind speed of 84 mph.
Lowering to 12" above tower top, failure is at 119 mph.
So, it could be useful in a modest installation.
73,
Gerald K5GW
In a message dated 3/15/2016 2:01:59 P.M. Central Daylight Time,
infomet@embarqmail.com writes:
Let’s not call names.
An EMT mast is great, as long as you don’t get greedy and make it too tall
outside the tower.
Mine is about 2’ above the tower top and I think it will survive any wind
likely in my area. And I really won’t cry if the $150 beam is damaged!
It’s several years old and shows no sign of deterioration. It cost almost
nothing and weighs next to nothing.
So I have a used tower, used tribander, used rotator, EMT mast, but new
coax.
I also have a HB amp made from used components, with an easy KW+ output.
It’s a rare pileup I can’t get through.
I am VERY happy, but may change to an LPDA so I can get the WARC bands,
someday.
I also use junk tubing from a kid’s swingset for Field Day. It’s worked
fine for a decade or so.
Successful systems can be designed around most any components, as long as
one doesn’t try to do too much!
I’d far rather see a ham put up 30-40 feet of used tower and a used
tribander than envy those with more elaborate, expensive setups!
A few more hours on the air will make up for a few dB of antenna
performance and there will be money left for beer.
Wilson
W4BOH
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