Whoops! Some other issues and comments I neglected to address in my last reply:
Conduit length and orientation:
To be clear, my conduit sticks will be oriented male end to female bell end, in the direction of the cable pull (from power pole to my transformer pad), to prevent extra friction at join points when running line and pulling cable.
Checked with my electrical supplier: I will take advantage of using 20' sticks of the 3" Sch40 PVC elec conduit that PowerCo spec'd, in order to reduce the number of cemented joints. I will be happy to prime and glue to get a good seal. This is not a job I want to do twice because I was compelled to save.. what? 10 seconds on a joint on an epic underground run...
Where did the 240V drop over 1500' run concerns come from?
I might have used a poor choice of words or misused terminology (thought I wrote 'primary feed' from nearest pole) in my original post. Apologies if I used improper language. Somehow a few concerned folks seemed to get the impression that I planned to take a 240V feed from the nearest pole's transformer, run it 1500 feet underground, and through some miracle of physics end up with a 600A primary service feed at my end, apparently with negligible voltage drop. I'm not exactly sure how we got from wondering about the best way to feed pull line through a long conduit run, (one rope? multiple sections?) to Ohm's law and figuring voltage drop on 240 volts over 1500 feet. I apologize for the confusion I somehow created.
The nearest utility pole supplies power to my neighbor's 1BR cabin which is 1/4 mile from the state road. PowerCo poles supply high voltage overhead then a line drops to a pad mount transformer on the ground. Transformer feeds the cabin with 200A / 240V primary service. Boy, if I can just figure out how I to pull a 240V secondary feed off that transformer, run it 1500 ft underground in plastic pipe, and end up with a 600A / 240V service at the other end, I'll forget the tree farm, invest in a trencher and all the conduit I can afford, and start my own power company. :laughing:
Kidding aside, the plan is for PowerCo to drop high voltage from the pole to the buried pipe (leaving neighbor's transformer alone) and run high volts underground to a pad mount transformer 1500 ft up the hill, leaving ample juice for the transformer to supply 600A / 240V to my non-residential service entrance and distribution point. That's what the PowerCo engineer and I have agreed upon.
So, what's your plan for the pull line now?
The engineer who will be on site to surpervise the PowerCo installation said 1/4" polyvinyl rope would be fine. They use it to pull their own line for the actual cable pulling task. Said a continuous length wasn't required for that as long as I could tie a clean splice knot that wouldn't unravel when pulling their line. That makes things easier--I am an old rock climber who hasn't forgotten ropecraft.
Since I won't have to work with a big 1000' spool of line, I'm inclined to do this one-time job using 100' or 150' lengths of the 1/4" poly the PowerCo engineer spec'd, stringing a few 20' sticks at a time on grade using the "monkey-wrench weight" method suggested here to thread each stick in order, and then carefully glue each threaded section on (being sure not to slop adhesive past the bell where it could foul the line) and splice knotting the ropes as required. It sounds less elegant and less efficient than pulling a mouse through with twine line and a shop-vac, but I the brute-force simplicity appeals to me for this one-off job. I can be careful with the glue, and if a little primer gets on the rope, it won't hurt. If I grow weary of repetitively pulling 100' lengths of rope through 2 or 3 sticks at a time, I can try the suction / mouse method on the 1000' length that follows the spec'd junction box at the 500' mark. I've got a 3500W generator that fits nicely in the loader bucket of my DK40SE and I bet the shopvac will fit as well. Then I'd use the threaded twine to pull the 1/4" poly rope PowerCo requested.
I've got one more walkthrough with the installation engineer before I order the conduit and schedule the trench work. I'll get the final details I'll need to submit for my county permit (and plan for trench inspections before backfillng, if required in my county). Thanks for all the great suggestions to consider, gotchas to watch out for, and I'll be sure to verify that my trench man's equipment can meet the depth *and* width specs that PowerCo requires.
Thanks for the generous feedback so far, and don't hesitate to point out any logic flaws, bad assumptions, continuity gaps in procedure, or just stuff that I've said that doesn't make sense. I'm very grateful for those willing to offer help and tactical advice. I appreciate every bit of time you folks have donated to try and help me do this right so I don't have to do it twice.
-Chip
Robiefield Mountain Farms
-A couple of things come to mind here
working with your conduit.
First build a simple light weight work table that you can
slide along the trench with the tractor on skids with
using 2 by 6's and using a plywood top.
The table can be three feet wide and foor feet high, I am getting there!!
Now purchase 4 Ridgid or Reed pipe vises with the open sides to create conduit clamps to mount on the table.
one pipe clamp will free both hands and allow proper cleaning and glueing of the joints.
The second pipe clamp will hold either the male or bell end securely while spinning the free piece of conduit to set the glue.
The third pipe vice will help center the third piece and allow you to clean and glue the other end which is locked in the vice.
Making a narrow table you can pull with the tractor to connect 2 or three joints together at one time will save you work and allow you to put conduit under the table top to use as you move along.
The area under the table top can store the supplies and couplers if you need to cut a bell end and replace it with coupler splice.
You can simply lower the pipeline on the ground as you connect it and then use the shop vac and a hand full of shopping bags ties together and suck them through from one end to the other BEFORE you lower the pipe in the trench.
Its easy to make a pipe roller to lower the conduit in the ground as it lies along the trench using a few small pneumatic tires making up a sling roller to lower the conduit in place with low stress on the conduit (its the same way pipeline is laid in a lot of places.
So in doing it this way you have the work right in front of you and you can control the pipe while spinning it to set the glue and simply lie it on the ground for the running of the twine and suck the grocery bag wad through after you check for leaks at the joints by listening for an air leak squeal by capping the far end temporarily.
We used a pair of pipe vices on a small table to splice 4160 with 3 conductors, 2 grounds, and a continuity line and heavy 480 trailng cable and it was a godsend.
I would build 2 16-foot tables and bolt them together end to end, add the lower shelf to store pipe joints, glue and cleaner and it keeps the pipe clean too.
Using 4 pipe vises would gove you even better control with the conduit if you used both 10 and 20 foot pieces or simply make it 40 feet long to work with 4 10- foot pieces or 2 20-foot pieces at one time and simply splice and move along after you are sure the glue has set.
If you pre-glued two or 4 joints together and slid them under the table top the gluing job will go even faster for you and lowering the conduit in the trench can be done with the tractor supporting the pipe sling as it advances along the conduit with no issues of stressing the conduit as it is all one piece now.
So in this way you can glue 48 pipe sets together using the pipe vices on the bench to get ready and have 40 foot joints under the work table ready to glue together using the 4 pipe vices on the tabletop along the trench.
Once you have the pipe vices on the table top the gluing will go quickly for you and then you can lower the conduit in the trench later after you suck the bag wad through with the twine then your pull rope later with a little cable lube.
You can glue 10 foot conduit joints quickly the same way and it will not be tedious as you wil have the pipe vices to hold it fast while spinning on the new piece.
As far as the twine zip line goes you can simply use an electric drill and coffee can to wind the twine through and then the pull rope, no point in making it harder to do with a cable spool at both ends winding it up by hand.
