Trenching suggestions?

KevinC_63559 · 2024-07-26T16:35:22-0700

Hi -

Solar panels are on order, MPPT charge controllers installed, mounting frames backordered...

Seemed like a good time to ask for some practical advice!

I'd like to bury my PV cables about 6-12 inches deep. Suspect 6 would be just fine. Nobody in a 50 mile radius rents trenchers... downside of being rural.

Looking for suggestions on how to dig a 6 inch trench through both ground and a gravel driveway. Not really looking forward to having to do 100+ feet with a pickaxe!

Any suggestions?

I have a full size tractor, but that would limit how close I could get to buildings.

Also: is grey PVC acceptable for running the 10 gauge wires through? No rules out here, upside of being rural - but don't want to do anything stupid either.

zanydroid · 2024-07-26T16:39:59-0700

SCH40 or SCH80 would be fine, you can pull THWN through it instead of PV.

6” is not code compliant depth.

KevinC_63559 · 2024-07-26T16:42:42-0700

zanydroid said:
SCH40 or SCH80 would be fine, you can pull THWN through it instead of PV.

6” is not code compliant depth.

What is? I know the utility did 4' for their 7200 volt lines, but that seems excessive.

OffGrid Tony · 2024-07-26T16:43:30-0700

KevinC_63559 said:
Hi -

Solar panels are on order, MPPT charge controllers installed, mounting frames backordered...

Seemed like a good time to ask for some practical advice!

I'd like to bury my PV cables about 6-12 inches deep. Suspect 6 would be just fine. Nobody in a 50 mile radius rents trenchers... downside of being rural.

Looking for suggestions on how to dig a 6 inch trench through both ground and a gravel driveway. Not really looking forward to having to do 100+ feet with a pickaxe!

Any suggestions?

I have a full size tractor, but that would limit how close I could get to buildings.

Also: is grey PVC acceptable for running the 10 gauge wires through? No rules out here, upside of being rural - but don't want to do anything stupid either.

Electric pvc conduit is grey in color. The deeper you get the conduit, the safer it is. I believe “code” says 18” but….
Personally I’m getting ready to do same. I’m renting a walk-behind trencher and going 12” deep (I don’t want a future shovel hitting the line). I’m gonna use schedule 40 white pvc plumbing pipe because it’s cheaper than electric (and I’m an electrician by trade) but it’s my property and who cares as long as it’s sch 40.

Supervstech · 2024-07-26T16:43:34-0700

Whatever you do, use the largest conduit you can afford.
Way easier to pull wires out to upsize if the conduit can handle it.

Supervstech · 2024-07-26T16:44:23-0700

KevinC_63559 said:
What is? I know the utility did 4' for their 7200 volt lines, but that seems excessive.

If gfci protected, the top of the conduit conduit can be 12" below grade if not, 18 to 24" is code depending on conduit type.

KevinC_63559 · 2024-07-26T16:45:31-0700

Supervstech said:
If gfci protected, the conduit can be 12" if not, 18 to 24" is code

GFCI PV charge cables? How the heck do you GFCI DC current?

Supervstech · 2024-07-26T16:46:20-0700

If a trencher isnt available, you can use a excavator, or a back hoe attachment for the tractor.

zanydroid · 2024-07-26T16:46:52-0700

KevinC_63559 said:
GFCI PV charge cables? How the heck do you GFCI DC current?

You don’t.

This is an exception for 120V 20A (I might have the special case details wrong)

You most likely cannot GFCI protect AC side of an inverter either bc there are no GFCI breakers listed for backfeed

Supervstech · 2024-07-26T16:47:33-0700

KevinC_63559 said:
GFCI PV charge cables? How the heck do you GFCI DC current?

I was just stating NEC rules.

At the entrance to the conduit, if GFCI protection is in place on the feeder, 12" is allowed.

It can also be 12" if under concrete.

Underengineered · 2024-07-26T16:54:30-0700

Not sure what kind of soil you have but maybe a power washer? Yes, YouTube it. Or rent an old school chain type ditching machine would be the cheapest. Next is renting a mini ex. After that it’s a friend with a rock saw. Prices go dramatically up from there.

going_commando · 2024-07-26T16:57:15-0700

beginner345 said:
reat o

zanydroid said:
You don’t.

This is an exception for 120V 20A (I might have the special case details wrong)

You most likely cannot GFCI protect AC side of an inverter either bc there are no GFCI breakers listed for backfeed

You are right, its 120v GFCI protected reduces the the burial depth to 12". Other than that is 18" of cover to the top of the pipe, so the actual trench depth is 18" plus the diameter of the conduit.

KevinC_63559 · 2024-07-26T17:06:08-0700

Supervstech said:
If a trencher isnt available, you can use a excavator, or a back hoe attachment for the tractor.

If I had one, last I checked such attachments cost $3000+

I was thinking more along the lines of something like this? It would be easy to attach to the tractor and I could get within a foot or so of the building. Could do the rest by hand with that pickaxe.

KevinC_63559 · 2024-07-26T17:07:16-0700

Underengineered said:
Not sure what kind of soil you have but maybe a power washer? Yes, YouTube it. Or rent an old school chain type ditching machine would be the cheapest. Next is renting a mini ex. After that it’s a friend with a rock saw. Prices go dramatically up from there.

All dependent on that "Rent" option, which doesn't work for me - nobody, even United Rent All, has ditching machines available locally.

timselectric · 2024-07-26T17:11:31-0700

One more note on the depth.
If under a driveway, the minimum is 24" .

DIYrich · 2024-07-26T17:15:45-0700

Rmc is 6"

42OhmsPA · 2024-07-26T17:21:12-0700

KevinC_63559 said:
If I had one, last I checked such attachments cost $3000+

I was thinking more along the lines of something like this? It would be easy to attach to the tractor and I could get within a foot or so of the building. Could do the rest by hand with that pickaxe.

I was going to suggest a single ripper tooth dropped on a box blade to get you started and a mattock to get the required depths plus the areas you can't reach. Looks like you are on the same path.

robbob2112 · 2024-07-26T17:47:42-0700

According to the 2023 National Electrical Code (NEC) Table 300.5, the minimum cover requirements for conduits under a driveway are as follows:

- For Rigid Metal Conduit (RMC) and Intermediate Metal Conduit (IMC): 6 inches (150 mm)
- For Rigid Nonmetallic Conduit (PVC): 18 inches (450 mm)
- For Direct Buried Cables or Conductors: 24 inches (600 mm)

These depths are measured from the top of the conduit or cable to the finished grade, surface of the ground, or surface of the concrete. Always check with local authorities for any additional requirements or amendments to the NEC.

outboard1196 · 2024-07-26T18:06:26-0700

If there is a flexible conduit that can be used a subsoiler pipe layer would be ideal.
with a ripper tooth the trench tends to fill right back in .

seneysolar · 2024-07-26T18:06:46-0700

If your tractor has a 3 point this will do most of the hard work, then its a breeze with a narrow shovel

seneysolar · 2024-07-26T18:07:22-0700

outboard1196 said:
If there is a flexible conduit that can be used a subsoiler pipe layer would be ideal.
with a ripper tooth the trench tends to fill right back in .

You beat me to it , but i use UF wire, direct bury

KevinC_63559 · 2024-07-26T18:17:52-0700

So, other than cost, any advantage of PV wire at $2/ft (for a pair) vs. THWN at$0.66/ft (for a pair) vs. Direct Burial (with a wasted ground wire) at ~$1/ft

zanydroid · 2024-07-26T18:19:36-0700

KevinC_63559 said:
So, other than cost, any advantage of PV wire at $2/ft (for a pair) vs. THWN at$0.66/ft (for a pair) vs. Direct Burial (with a wasted ground wire) at ~$1/ft

Mostly disadvantages for PV, since you probably aren’t running 1000V or 2000V system voltage. At 600V THHN works fine is cheaper and easier to pull and works with smaller conduit

How is the ground wire wasted? You have to bond your array back to the same EGC as the inverter

Hedges · 2024-07-26T18:32:18-0700

DIY cable plow?

KevinC_63559 · 2024-07-26T18:32:57-0700

Hedges said:
DIY cable plow?

View attachment 231547

Oh... that is sweet!

Trenching suggestions?

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