Some speculation about the source of the twist of cables in conduit:
If you pull twisted cable (e.g. 3 x 6ga + 8ga) or twisted pairs or a
single stranded wire, then there is a source of (un)twist, or pull with
3 strand rope then there is a source of (un)twist or unspool off the end
of the reel then there is a source of twist.
Why properly un-spooled coax or a covered untwisted bundle would twist
if pulled with not twisted braid rope or flat pull tape (webbing) is a
mystery to me. Maybe it's a law of nature. It's easy to see if flat
webbing has any twist and difficult to insure there is no twist in braid
rope. I noticed the power company uses spooled braid rope for pulls and
swiveled Kellem pull grips. So the pros use swivels, but that may be
to keep twist out of their rope since the cable is twisted.
Once off a cable spool, you can be pretty sure somebody has put twist
into a cable, unless they were very careful to flake it in a way to
prevent twist.
I've left multiple messengers in my conduits for the future, but pulled
very few additional cables, so really don't know what went on inside
when I pulled with flat pull tape. Next pull, I will keep the tape flat
at the exit and spool it as I pull it out and see how much twist there
is when I get to the cable. I use flat conduit measuring tape to pull
the flat pull line, so there is (hopefully) no twist put in by the
messenger. see
http://www.garvinindustries.com/Tools-and-Installation-Accessories/Wire-Pulling-and-Conduit-Installation/Conduit-Measuring-Tape-Pull-Line-and-Pull-Tape
The conduit measuring tape has 180 lb breaking strength so it will work
for short straight pulls of a few cables. A 3000' spool is a lifetime
supply for measuring, small stuff tying, messengers, etc.
Grant KZ1W
On 11/26/2011 3:47 PM, Steve Jones wrote:
> I'm getting ready to pull wires and cables through the conduits to my new
> tower, and I want to include an additional pull rope for future cables. My
> 3" ID conduits will be initially very lightly loaded, so I'm sure there will
> be plenty of room for extra cables later. But I understand it is common for
> a bundle of wires to twist while going through the conduit, thus wrapping
> the "future" pull rope around the wires and rendering it useless for future
> pulls. Any suggestions on how to void this problem? I was thinking maybe a
> swivel on the bundle would reduce the tendency of the bundle to twist during
> the pull...?
>
> 73,
> Steve
> N6SJ
>
>
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