How to build a rocket workshop (part 7: the burial)

Step #2,352: dig a trench.

In order to run electrical wire and conduit from the main electrical panel in the house out to the shed, the electrical code requires (more on this later) that the conduit be buried a minimum of 18 inches underground.

digging completed – view from above

This requirement is totally understandable, given the nature of electricity and the danger of someone accidentally digging into it. It is also burdensome. It fact, is much more burdensome than it seems. This is partly because 18 inches is deeper than it initially sounds, and the difficulty increases exponentially as you get further down. If you’ve ever done any digging in your yard, even just to replant a small plant or bush, I’m sure this will resonate with you.

The minimum depth applies to the top of the PVC conduit, and you need to err on the side of too deep rather than too shallow if you want to make sure it’s up to code and will pass an inspection, so the trench really needs to be about 20 inches deep.

But the most difficult problem you immediately run into – if you’re me – is the soil quality. This is soil that nobody has touched in many decades. It’s dense and compressed, like clay, and also rocky. I mean extraordinarily rocky. There were points during which I achieved maximum rock, i.e., there was no soil at all and just pure rock.

pile of large rocks and stones, with a Starbucks cup for scale
sample of large rocks I dug up, with cup for scale

I had nothing other than a simple garden shovel. I went out on a limb and halfway through the project bought something that is specifically made for digging trenches, which looks just like the shovel except it’s somewhat narrower. This was helpful, but the digging was still brutal.

I’d estimate digging this trench by hand took about 50 percent of the total time for this electrical project, with the other half being everything from drilling and cutting and bending conduit to actually running the copper wire inside it and installing outlets and light fixtures (for which, as mentioned in the last post, my friend Darrin was invaluable and did all the heavy lifting, literally and figuratively). In retrospect, maybe I should have brought in some kind of heavy machinery to dig this trench.

Did I mention the sheer quantity of rock?

another large pile of rocks
maximum rock

Anyway, the trench was simple enough, conceptually. And from the main electrical panel in the house to the shed, only about half had to be underground. The other half is above ground and runs along the outside of the house.

Below is a picture of the trench mid-project, when I was busy naively underestimating the 20 inch depth requirement. It’s getting there, but by no means complete yet. You can see where the conduit comes up out of the trench, above ground, in between the door and the gutter downspout. We also installed a new junction box with electrical outlets and weatherproof cover there, just because we could.

View of L-shaped trench dug in ground, surrounded by piles of dirt and stones
a straightforward trench

Below is the view underneath the front of the shed, where the 1″ diameter conduit goes up inside the shed to a sub-panel. The smaller 1/2″ conduit on the left here contains copper wire, running from the shed’s sub-panel to the copper ground rod that you can see here.

As an interesting aside: with any electrical panel, you need to have at least one copper ground rod, and this comes in a standard length of 8 feet. The metal rod must be buried underground and attached via copper wire to the panel. In other words, you have to drive the rod straight down into the ground.

If the soil quality is good and its resistance is low enough, you may be able to get away with just a single 8′ ground rod. In our case, the soil was abysmal, and we needed to drive two separate 8′ copper rods into the ground. You’ll never be required to use more than two rods.

Outside shed, close up view of pvc conduit in trench and copper grounding rod
pvc conduit and copper grounding rod

Here are two final pictures of the trench once it was dug further down to the required minimum depth, and we laid the conduit inside.

view of trench from house, with PVC pipe laid in trench
trench from house

As this project went on, we needed to leap across increasingly wide and deep trenches, countless times. Particularly awkward was the trench needed to pass directly in front of the shed door, which required Olympic-level gymnastics to vault across the ditch but also simultaneously duck your head to avoid hitting the top of the door frame.

Eventually we realized it would just be easier to throw together a few wooden bridges made from lumber (2x4s or 2x6s). This prevented more injuries and also was a good idea for the inspector who still needed to come on-site after all the work was complete.

view of trench continuing to shed, with PVC pipe
trench continues to shed

If you look closely (and maybe squint), you can also see in a few of these pictures that we came across some unexpected pipes and drain tiles. We called 811 before digging – required by law – and the various utility companies came out to ensure there was nothing buried underground in this area.

But there were drain tiles, which are not part of any utility but are just part of the property. These were loosely connected and immersed entirely in tons of rock, to facilitate water drainage from the house, and we hit them in two separate locations as they cut across the trench. We also encountered some other pipe (about the same size as the drain tiles, roughly 4 inches in diameter) whose origin and purpose were unclear. We just dug around and beneath it, without disturbing it, and continued on our way. That pipe remains shrouded in mystery.

The conclusion here is simple and painfully obvious: digging sucks. But it was a necessary step to bury the copper wire and conduit in order to comply with the electrical code. This was the most backbreaking part of the project but also allowed for the more fun electrical wiring to be completed in the shed (covered in the last post).