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HELP! I need a wire stretcher :)

S

Steelart99

New Member
Joined
Aug 5, 2024
Messages
187
Location
Colorado
Several weeks back, I dug a 350-ft trench, laid in PVC conduit and pulled 5 wires through my conduit. Backfilled, packed, marked with metallic ribbon (for metal detector), and moved on to installing my inverter, battery, etc. We'd had snow coming in as I finished up pulling the wires, trimmed them and spooled up the end of the wires.

So, today I finally got back to the wiring of the panels starting with the long run from my combiner box to the garage. And ... promptly saw that I had cut all my wires about 3-6 foot shorter than I need them to be. Sigh ...

So, how do I go about stretching my wire???

Okay ... so really, what would be the best technique to extend my wiring (8 THWN-2) and protect the joints? The new joints will be inside the PVC conduit.

Approx 430VDC and 13 Amps for this run.

Alternately, I can move my combiner box to a less optimal location, but "should" be able to use the wire length as-is.

Thanks in advance.
 
Steelart99 said:
Several weeks back, I dug a 350-ft trench, laid in PVC conduit and pulled 5 wires through my conduit. Backfilled, packed, marked with metallic ribbon (for metal detector), and moved on to installing my inverter, battery, etc. We'd had snow coming in as I finished up pulling the wires, trimmed them and spooled up the end of the wires.

So, today I finally got back to the wiring of the panels starting with the long run from my combiner box to the garage. And ... promptly saw that I had cut all my wires about 3-6 foot shorter than I need them to be. Sigh ...

So, how do I go about stretching my wire???

Okay ... so really, what would be the best technique to extend my wiring (8 THWN-2) and protect the joints? The new joints will be inside the PVC conduit.

Approx 430VDC and 13 Amps for this run.

Alternately, I can move my combiner box to a less optimal location, but "should" be able to use the wire length as-is.

Thanks in advance.
Click to expand...
I would move the combiner box
 
Steelart99 said:
Several weeks back, I dug a 350-ft trench, laid in PVC conduit and pulled 5 wires through my conduit. Backfilled, packed, marked with metallic ribbon (for metal detector), and moved on to installing my inverter, battery, etc. We'd had snow coming in as I finished up pulling the wires, trimmed them and spooled up the end of the wires.

So, today I finally got back to the wiring of the panels starting with the long run from my combiner box to the garage. And ... promptly saw that I had cut all my wires about 3-6 foot shorter than I need them to be. Sigh ...

So, how do I go about stretching my wire???

Okay ... so really, what would be the best technique to extend my wiring (8 THWN-2) and protect the joints? The new joints will be inside the PVC conduit.

Approx 430VDC and 13 Amps for this run.

Alternately, I can move my combiner box to a less optimal location, but "should" be able to use the wire length as-is.

Thanks in advance.
Click to expand...
Sounds familiar :fp2

All conduit generally builds up moisture inside, especially outdoor. A crimp in conduit will be exposed to higher humidity, even condensate. DC is an instant electrolysis problem. Wire splices aren't allowed inside conduit per NEC (for good reasons). If you can't move the combiner box, do like someone else suggested and have a new junction box above ground, where you can service it, and where water won't accumulate. Do your "wire-stretching" there %^)
 
I didn't catch that wire splices were not allowed inside conduit. I frankly didn't like the idea of having any splice ... but "life" happened.

I'll just move the combiner box or look into how to add a protected waterproof junction box (which I hadn't thought about!!!)

Thanks guys

IMG_8390.JPEG
 
Yeah I've done that before too.

Back up about 10 ft, dig down and expose the conduit. Carefully cut it without cutting into the conductors. You can use a PVC cable saw. Attach a pull line before you pull the conductors back. Slide a conduit ell down over the conductors, bring them up a couple feet above grade. Put in a post and a junction box you can make your splices in. Use listed insulated wet location splices, like Burndy taps. Then carry on with your new conductors and another ell connecting to the existing buried conduit. That way your splices will always be accessible.
 
Just an update that I did add a junction box and moved my combiner box ... I'd mounted it too low ... what was I thinking? I'm still waiting on my butt joints to join the wires, but at least I pursued the great options brought up here. Thanks

IMG_8413.JPEG IMG_8414.JPEG
 
Last edited:
Your anchor bolts in top of concrete footing is a lot better than lag screws into end of pressure treated lumber that another guy did. But still, have you analyzed what pull-out force those bolts could experience in a high wind? And what shear force on the pair of bolts for upright strut?

I prefer to see a "wide stance" to avoid applying torsion to the upright. Like have the angled strut hit side of footing much further from the one bolted bracket you've got.
 
I just had to post this.

My electrician buddy would always joke about getting the "wire stretcher" out of his van when I would help him on jobs.
In October I found this at Tractor Supply!

IMG_2681.jpg

Unfortunately my friend isn't around anymore to appreciate the joke, but I hope you guys do.
 
Hedges said:
Your anchor bolts in top of concrete footing is a lot better than lag screws into end of pressure treated lumber that another guy did. But still, have you analyzed what pull-out force those bolts could experience in a high wind? And what shear force on the pair of bolts for upright strut?

I prefer to see a "wide stance" to avoid applying torsion to the upright. Like have the angled strut hit side of footing much further from the one bolted bracket you've got.
Click to expand...

I did get the structural analysis that EG4 did on these mounts. I wasn't thrilled with the results but ... here I am. Supposedly good to 105 mph wind. I couldn't really understand how they did the snow loading analysis; it didn't make sense to me and structural analysis had been a part of my career. Fortunately, the panels shed the snow load fairly easily (give my two test snow storms).

I'd thought about adding diagonal braces down to the concrete pillars also, but I was pleasantly surprised with how ridged the entire mount was once fully assembled. Anchor bolts and assembly bolts ... I don't know what to say about these as there can be so much variation in construction and assembly that it would be futile to guess how well it will hold together. The shear load capability of the bolts on the upright would be more than sufficient. The panels would fail before the bolts had any issues (in my opinion).
 
I'm electrical not mechanical, but I can do some calculations.

Shear of the anchor bolts I don't expect it to be near limits. But what pull-out force did you get for the bolts? And what are their safe load limits? (big difference between pullout of a redhead expanding anchor, and pullout of an L-bolt hooked under rebar.)

Shear on the bolts holding uprights I'm curious about. Interesting rhombus shape and the bolts appear barely an inch apart. Might mash some aluminum and make it less rigid.
 
Hedges said:
I'm electrical not mechanical, but I can do some calculations.

Shear of the anchor bolts I don't expect it to be near limits. But what pull-out force did you get for the bolts? And what are their safe load limits? (big difference between pullout of a redhead expanding anchor, and pullout of an L-bolt hooked under rebar.)

Shear on the bolts holding uprights I'm curious about. Interesting rhombus shape and the bolts appear barely an inch apart. Might mash some aluminum and make it less rigid.
Click to expand...

The pullout force of the anchor bolts tends to be driven by the hole prep,. I didn't try pulling them out with my skid steer, but I did put considerable torque force on the bolts when getting them set in the holes. More torque than the final torque at assembly. I did have a couple that did not hold as well as I'd like them too though.

Here is the structural analysis report:
 

Attachments

Steelart99 said:
The pullout force of the anchor bolts tends to be driven by the hole prep,. I didn't try pulling them out with my skid steer, but I did put considerable torque force on the bolts when getting them set in the holes. More torque than the final torque at assembly. I did have a couple that did not hold as well as I'd like them too though.
Click to expand...

When I did my ground mounts, with 1/2" bolts inserted into drilled holes in an existing patio slab, one didn't bite. The rest held pretty well.

Steelart99 said:
Here is the structural analysis report:
Click to expand...

Steelart99 said:
... structural analysis had been a part of my career.
Click to expand...

Can you find in the structural analysis report a calculation of pull-out force experienced by the bolts?
I don't even see the relevant dimensions labeled.
 
Hedges said:
When I did my ground mounts, with 1/2" bolts inserted into drilled holes in an existing patio slab, one didn't bite. The rest held pretty well.





Can you find in the structural analysis report a calculation of pull-out force experienced by the bolts?
I don't even see the relevant dimensions labeled.
Click to expand...

There is no specific section on the pull-out force on the anchors. That said, the required torque level, if met, implies that the anchors will not move for the required force level. I hope that made sense.

When these were installed, I dropped in the anchor, put on just the washer and nut and cranked down hard on the nut until everything stopped moving. Then I removed the nuts/washers and installed the bracket. After reinstalling the nut/washers I torqued to the required level (called out in the instructions) and only had two bolts (out of 80 anchors) that didn't quite reach the torque level without moving upward. Even these two eventually locked in at the correct torque, they just stood proud of the bracket further than I liked.
 
Steelart99 said:
My wire run from the house to the array is 18-24" ... but I did go a bit shallower under my array where I'm just trying to keep the wire mess down. shrug
Click to expand...
As long as your AHJ is fine with it youre good to go.

I planned to use direct burial cable for my source circuit runs, at 24 inches per code. First ran a water line in the same trench at 30 inches for frost. Was planning to cover the water line with 6 inches of soil before laying the cables.

AHJ came out to inspect the water line, wanted a foot separation between water and wires, so asked me to raise the direct burial cables up to 18 inches. Not Code but that's why they call him the AHJ. Needless to say, I didn't argue with him.
 
Steelart99 said:
There is no specific section on the pull-out force on the anchors. That said, the required torque level, if met, implies that the anchors will not move for the required force level. I hope that made sense.

When these were installed, I dropped in the anchor, put on just the washer and nut and cranked down hard on the nut until everything stopped moving. Then I removed the nuts/washers and installed the bracket. After reinstalling the nut/washers I torqued to the required level (called out in the instructions) and only had two bolts (out of 80 anchors) that didn't quite reach the torque level without moving upward. Even these two eventually locked in at the correct torque, they just stood proud of the bracket further than I liked.
Click to expand...

Their structural analysis covers the more difficult part, converting wind speed to horizontal force on array.
Give height and width, that can be converted into pull-out force on bolts. It is basically acting as a crowbar.

1733671621806.png

"𝐹5 = 16137 N" horizontal force per upright
Consider applied midpoint of array, about 1m above metal bracket and anchor bolts.
Length of bracket about 0.1m

16137N x 1 / 0.1 = 161370N pull-out force applied to 2 bolts
36275 N per bolt, 18138 lbs. pull-out force per bolt.

If we didn't apply mechanical advantage , height of bar divide by length of foot, this force would be between safe working load and ultimate load of the anchor.
Including that 10x multiple, calculated pull-out force far exceeds ultimate load. In 105 mph wind.

I think it will bounce with gusts, and dynamic loading will exceed limits in lower wind.


(What I didn't follow is why the analysis compared X-direction of wind force to 4x weight of panels and base, calling that load capacity:

𝐹𝐹5 < 4Wp + 4Wc )
 
Steelart99 said:
I had planned with going with the butt joints below along with a marine grade shrink tubing. If it didn't look satisfactory, I'd even planned to use these splices followed with soldering the joint. Then add the shrink tubing
:
Click to expand...
Yes. I use butt connectors and waterproof shrink tube to connect a submerged water pump.

However in a junction box, I use the mechanical connectors.

You do you though🙂. There is almost always more than one way to skin a cat.
 
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