LOOONNNGGG Underground Cable Run

[Illini22]

I have nothing against conduit ( my whole house is in it). I just plowed some in with a subsoiler. Conduit is beneficial crossing roads, parking lots under patios etc. I wouldn't say it will be repaired sooner if it's in conduit. You can thump a primary, call your locates in and dig/repair pretty quickly on private property, downtown is another story. In conduit you have Pull out the old, load the new install, terminate, etc. It can be done quickly to UNLESS, it's not a fault but a "digin" ( hit by others). Then your gonna be out alot longer than if it was direct bury (just splice the damaged area). They will be replacing transformers, risers (the pothead termination) etc. And if your lucky the wires going to your service entrance won't be torn off the side of your house, in which case the utility may have there equipment repaired and livened but your still out a day or to because of your electrician. I've seen it many, many times ( I'm sure north fl. Lineman has too). Both installations have there merits based on conditions and locations, it's not a simple answer as on is better than the other. I've fixed primary faults in mud holes a pig wouldn't step in, oh I wished they had used conduit on that job.

 

[robiefield]

Wow, what a great response. I love this place.

I tried to keep things simple with my question, because I was interested in the procedural approach to the conduit-and-pull-rope assembly task, and I know that mixing overconfidence and naievete can be more dangerous than explosives. And I do blow stuff up from time to time, speaking figuratively (well, in most cases...)

Let me add some more info. There's some great help here for me, but some of it's diverging on issues where matters are solidly in hand. (But the concerns are valid, and I appreciate the precautionary attention to them.)

I'll try to address the existing areas of contention but it's gonna have to get longer and more detailed than simply working out the best method of running line through 1500 ft of conduit. But since y'all asked, here we go:

Item: Get in touch with the PowerCo.
Not to worry. I'm very much in touch with PowerCo. My contact is the engineering manager for the region. I've been in contact with the field engineering department since 2007 on an annual basis while I cleared land and built critical infrastructure. I've had three site visits. We just finished a feasibility analysis that evaluated overhead and underground alternatives from several dimensions.

Potential approaches from the two closest high voltage sources (east and west) were considered, with attention to factors of terrain, easement access and permissions, overhead and underground materials and labor costs for PowerCo to supply the physical transmission infrastructure, and the customer-borne cost to provide the cleared land dimensions required for each transmission path and method. The fact that I am in a mountainous region with slopes 45 degrees and greater in places, and that the unimproved land I own is densely forested including old growth hardwoods, is a significant variable.

Full cost scenarios were performed for each approach direction and transmission method. Each cost scenario included PowerCo cost passed on to customer as a requirement of the installation, as well as the customer-borne cost to clear the forested path necessary for each transmission method. Under rural extension requirements, the customer bears the full cost of clearing along the transmission path.

I should also note that this project is not designed to supply residential power at this time. I have the geographical exposure, altitude, and soil type to support the Christmas tree and fruit orchard I am building. This requires infrastructure in advance of crop planting--a well capable of agricultural irrigation, planting locations relative to the well (distance and elevation considerations), necessary outbuildings including equipment barn, workshop, office, boondock living quarters, and so on. The location of the service entrance as a distribution point for secondary power runs to existing and planned infrastructure is also a critical design consideration.

The non-residential status of the land determines the costing approach as well as the portions that the customer and power company pay for. The rural extension non-residential classification for power transmission places almost the entire cost burden on the customers.

Folks, it's gonna be expensive and I am just one guy who's managed to get this far by excruciatingly tight resource management and a metric buttload of sweat equity. I don't have the resources of a wealthy family or corporate entity backing me. I'm a working-class schlub with two full time jobs and a time-phased dream feeding on carefully planned cash flow.

Issue: Voltage drop over distances! V=IR!
I'm right with you. I'm an engineer. I won't bore you with my professional resume and I won't try to impress anyone--I'm here asking for help. I have facility, control system, machine, and circuit design and implementation experience. You can't do this stuff without a thorough understanding of spark juice. Unlike the commercial world, on my farm, I can have a meeting with investors, management, engineering, finance, HR, construction, production, legal, facilities, landscaping, legal, IT, maintenance, customer service, and janitorial staff... in a two-hole outhouse. You get the picture--DIY, baby. I've timbered, stumped, and cleared land, built, wired, and plumbed outbuildings from slab to ridge vent, cut and graded roads, just like many self-sufficient folks here. (See why TractorByNet is useful to me?)

I've learned to research, plan, and execute, and I'm 100% responsible for consequences, no safety net. It's not what you think you know, it's what you thought you knew that you really didn't know that gets you. I'm not 20 and omniscient anymore. I do know I've got zero experience with the task of threading pull rope through over a quarter mile of conduit. I figured the collective experience here would be a great way to avoid costly mistakes of inexperience.

The 1500' of conduit will carry the high voltage feed to a pad mount transformer adjacent to the agricultural well house where the service entrance has been approved by PowerCo and is in the process of county permitting. The design that PowerCo and I created together supplies 600A to the service entrance. The box there will feed 50A to the well house (deep well, 5 hp pump), then from there drop runs of 100A to equipment barn and shop, 50A to the temp living quarters (RV), with 400A remaining capacity to supply future ~4000 sq ft home and office complex to be constructed in fall 2013.

Powerco engineering manager who will oversee the operation on site provided me with the Sch40 3" PVC elec conduit spec. He also spec'd 1/4" nylon rope which his crew will use to thread their own pull wire for a mechanical puller. PowerCo supplies and pulls the high voltage insulated cable. PowerCo spec'd 24" wide sweep ells at entrance, at junction box (future supply point spec'd by PowerCo for adjacent property owner) at 500' (2), and at transformer. (PowerCo did *not* spec Sch80 for the ells--double checked this.) Said the 1000' segment would not need pull box at halfway point. All this will be documented in the detail design doc/drawing I will use for permitting. Signed off by both me and PowerCo.

Project management's doing good, but all steps of execution are not complete and defined at the sub-task level. I admit it--I want to look like I've got my act together in front of the PowerCo Sr Engineer. I didn't want to ask *him* the process question about threading the conduit--not his area of responsibility. I want to be able to deliver my commitment to have a trench with threaded conduit as spec'd ready when the PowerCo install crew arrives. So I thought to ask here to see what I could learn. You guys didn't disappoint, nosirree! I sure as heck do not know it all.

Issue: Moisture in Conduit
This has been discussed with PowerCo contact. Some condensation due to thermal variation expected, high voltage feeder cable has very thick insulation designed for this. The industry standard of cemented conduit (thank-you!) in 36" min depth (code for my county) will be followed. PowerCo also specs sand or screened fill dirt fill for cuts through rock where long term incremental abrasion can create fractures. Conduit will be oriented male-to-female to facilitate smoothest cable pulling. (thank-you!)

Issue: Why aren't you just going with poles--less expensive, right??!
Again, rural extension requirements and my individual use case, distance, thick forest, and steep terrain are impacting factors. Non-residential service, Customer pays all cost and negotiates all easements to clear power path. Customer must clear and remove all trees, vegetation, undergrowth 40' across entire length of pole path. If trenched, customer clears trenching path (app 10'). PowerCo will trench or Customer can perform trench work at own expense. Same with the conduit. PowerCo rates for trenching and conduit are $$$$. PowerCo contact has approved use of existing cleared easement road (with conduit) for trench path which is shorter run than pole path. Pole path crosses road 3 times due to terrain slope, longer runs. Pole path requires more complicated easement agreement and must plan for clearing, stumping and disposal of timber / stumps to neighboring property owner's specifications. So, let's think of DIY man felling, limbing, bucking, stumping, removing timber and slash in very dense forest (40' to 120' tall pine, oak, poplar, black gum) for ~1700 ft x 40 ft zone to facilitate the "cheaper" option of overhead power. How long would it take you fellas to do all that with only a helper for a 40' wide 1/3 mile long path through thick briery steep sloped woods, working 2 10 hour days on weekends? Vs trenching existing, flat, NO clearing-required road which follows shortest possible path. (And I have a trenching contact who owes me money and will trench this job for under $1/foot...)

This might be unacceptably long for this forum, but expanding the problem description to include scope, qualifications, research, contacts, approach, planning, permitting, scheduling, and execution sure does suck up text space. And the somewhat-interesting-to-read-without-feeling-like-work forum factor goes all to heck. But, it seemed the best way to address the Monte Carlo scenario questions that arose from my brief initial question and the cautious approaches from you concerned folks with experience. Thanks if you made it this far and are still reading.

I don't think I know it all. I know da** well I don't. I'm no genius. I'm just a guy who's willing to do the homework and the sweat work, to bust butt to make a lifelong dream happen on a budget and conservative financial approach. Not afraid to do any kind of hard, hot, or dirty job, but have learned well the value of leased wisdom from veterans in the (I think it's appropriate here) "trenches".

I've got my hands full, folks, but with a little help and guidance and a lot of sweat, planning, and determination, I can do this too. Nobody special, just a guy lookin' for some help in a hands-on process I've not done before.

Thanks for all the tips and reminders. I'll post updates as the process moves forward. I'll be honest and share screwups as well as successes. DIY man gotta keep it real, otherwise finance and HR and investors all kick my butt, and I hate beating myself up without help.

Best
Chip
Robiefield Mountain Farms

 

[robiefield]

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

 

[Illini22]

Chip, we also use 1/4" line on overhead, we call it pea line. After you tie your bowlines or other knots make sure you tape the tails so your knots don't unravel. Our spools came in about 2200'-2400', very light, maybe 15lbs at most. Put a pipe thru the holes and away you go. Another thing that may help if your alone. start so your always putting the next stick (male end) into the bell end, that way you won't have to prop up the end of the pipe if you did the opposite. The bell end can be on the ground because the male will go inside it, we always have a sledge hammer to make sure it's in all the way but 3" it shouldnt be needed much ( maybe if there's a burr). If you use 100' lengths with knots I would use that to pull a continuous rope to eliminate knots.
If your piping to vaults, handholes or splice boxes your pipe depth will need to be about a foot deeper than the bottom of the vault to compensate for the 45 degree bend on the sweep. Our handholes are about 36" deep. You want your conduit with the sweep to barely come in the vault, and just a couple inches above the gravel base, near the corners of the vault. I would have a couple of slip coupling around just in case.

 

[tommu56]

One thing if you are going up hill to the transformer pad I would pull down to the pole from the transformer and let gravity help you hence change the direction of your bells to make an easier pull

again just my opinion

tom

 

[robiefield]

Chip, we also use 1/4" line on overhead, we call it pea line. After you tie your bowlines or other knots make sure you tape the tails so your knots don't unravel. Our spools came in about 2200'-2400', very light, maybe 15lbs at most. Put a pipe thru the holes and away you go.

That's really helpful. I'd even bet the price of one of those spools from an electric supplier would be less than what I'd pay for the separate lines to tie together from the Big Box Bldg Supply Store. I could run a dowel through the spool center and temporarily hang it off the ROPS of the DK40 and feed it out that way. No need for knots, no need to pull entire 100' rope lengths through every stick one at a time. This is why help like yours is worth more than money, it's time and know-how without having to work it all out on one's own.

Another thing that may help if your alone. start so your always putting the next stick (male end) into the bell end, that way you won't have to prop up the end of the pipe if you did the opposite. The bell end can be on the ground because the male will go inside it, we always have a sledge hammer to make sure it's in all the way but 3" it shouldnt be needed much ( maybe if there's a burr).

More good stuff. You bet, I'll put the sledgehammer, a sawzall, and a grinder along with the primer and cement in the tool kit for the day's work.

If you use 100' lengths with knots I would use that to pull a continuous rope to eliminate knots.

It looks like if I can get a spool like you mention from the elec supply shop, I can run the line off the spool like you mentioned (still using the wrench weight to chuck it through each 20' stick) and run the whole thing without the need to knot or tape splice knot ends. This is great, the process is improving on paper before I'm out there on a schedule and deadline.

If your piping to vaults, handholes or splice boxes your pipe depth will need to be about a foot deeper than the bottom of the vault to compensate for the 45 degree bend on the sweep.

My PowerCo contact mentioned putting a junction box 500' from the pole, in order to provide future high voltage tap-in availability to the adjacent landowner. I'll be sure to account for the dimensions of that box and ensure that the 24" sweep ells entering/exiting that box have the right vertical positioning relative to the box and trench depth. Thanks for that note.

I would have a couple of slip coupling around just in case.

Yup. No brainer. I was planning on keeping a handful of slip couplings and a couple of ten foot sticks, 'cause I know that 25 20' sticks does not equal 500' feet of conduit due to the overlap at the bell connections, so a few pieces and parts to meet positioning requirements are well worth having.
Thanks a ton for the thoughts. I appreciate it.

 

[robiefield]

One thing if you are going up hill to the transformer pad I would pull down to the pole from the transformer and let gravity help you hence change the direction of your bells to make an easier pull

again just my opinion

tom

Thanks, Tom. I see your point. However, the easement road elevation change from nearest pole to my transformer pad placement is only about 25 feet (unlike most of the terrain on either side of the road bed.) If I'm threading pull line by chunking it through each stick with a crescent wrench weight (before cementing together) the road grade doesn't really matter for purposes of threading one stick at a time with my pull line.

Again, PowerCo is required to pull their own cable. It's not a negotiable option. I'm just providing the pull line for them to use to pull THEIR pull line and they use their pull line and whatever type of power puller they have to run the big cable. With their setup, I doubt PowerCo would care either way, and regardless, the cost to them is all the same. The whole run will have pull line from end to end, PowerCo guys are gonna choose which end they start from without asking me anyway!

But this is all good--I see the way folks are thinking, identifying potential sources of friction and opting to take advantage of natural assistance such as gravity where ever possible. It's a problem solving state of mind that makes a lot of sense. And I appreciate you sharing that.

 

[bubbas45]

They told me that costs have changed over the years to where it's cheaper overall for them to install it underground.

Lucky you. We are looking into this for our property, with about a 1500-ft run the short way or half a mile the long way. In NH, PSNH currently charges almost $10/ft for overhead power, but almost $13/ft for underground power. That $13/ft is after you supply the trench, the conduit, and the screened fill. (And of course the pad and transformer.) I don't understand the why's of this pricing scheme. They are saving current and future labor, as the underground line will be safe from future ice storms. But that's the way it is here.

Trenching in the Granite State is often difficult.There's a good chance on our property of hitting ledge or big boulders that will require a hydraulic hammer ($2500 minimum charge) or explosives ($1500 minimum charge).

I'm still trying to get all the numbers to run, but off-grid solar (plus backup generator which we would have in any case) is getting feasible (with Fed tax credits).

bws

 

[jonyyuma]

Okay, Now the rest of the story comes out...You did have an idea about putting it overhead...Been there done it many times, now on I will just read. I see that many other professionals answered, including a few linemen.Your first post looked to be a disaster, especially about not glueing pipe joints, just waiting for bankrupting your efforts. Best method of install a pull line is blowing it thru with sponge or industrial vac sucking it. Most of the time it is poly and looks like binding twine. Previous poster showed a bucket of it.The second line looks like ski rope for water skiing, and best is poly, but we have used nylon..We have never pushed a line while installing and glueing.You should Be glad you are not threading and screwing rigid pipe.

 

[cttractor]

Chip, one of the things that has burned me from time to time is a length of PVC pipe having and end that's been driven on or squeezed so that it's out of round, but not so much so that you notice it in normal handling. Whether it's the straight end or the bell, once you've glued the good end into your system and go to fit and glue the other end, you find you can't get it to mate. If the pipe is small, you can force it in. But as you get into bigger pipe (3", 4" and larger, it's thicker, stronger, and becomes difficult to impossible to do alone, sometimes even with a helper. If you try a quick fit on both ends of each piece before using it, you can then put a bad one aside and return them for a swap the next time you go to the store. The other alternative is to do that test on both ends in the store when you select the pipe. It's quite frustrating to have a piece glued into the system and then find the other end is bad.

This is just one hassle I thought I'd mention because you're going to be using many lengths.

Good luck!