I currently had an irrigation pump and small shed 125' away from my main panel. This pump and shed electric is fed underground in 1" pvc pipe with #10 THHN 220v (neutral/ground/2 hots). I removed the shed and am building a larger workshop with a cement floor slab. The slab will contain the two wells, one for irrigation and the other is house well water supply. here's a pic of what it looks like now. enter image description here As you can see i have the irr pump wired up temporarily for now until the slab is poured.

I plan to leave the existing 4 #10 wires and pull an additional 4 conductors in the 1" pvc pipe for a new 60 amp feed. 2 #6 Black&Red Hots, 1 white #8 neutral & 1 green #10 ground. I went with the minimal sizing on the neutral and ground wires because of the possibly difficulty in getting these pulled through the 125' of pipe.

The pvc pipe will terminate into a square D DU323rb shut off box Text

This shut off box will be mounted 5' off the ground with the new conductors (2 hots & neutral) going to the 3 phases of the shut off box and the existing 4 conductors dropping down out of the shutoff in pvc to a disconnect box like this.


The irrigation pump will be wired directly from this disconnect box.

An 8' ground rod will be driven next to the slab under the shut off box and connected to the ground in the shut off box with #6 bare.

The new 60 amp feed will run from the shut off box to an interior load center, something like this Text

Which I will break into 20 amp circuits for lights, house well pump, shop equipment, Mini Split AC.

Just looking for comments and suggestions if anything stands out as incorrect?

Should I just remove the existing #10 wires and go with 4 #4 wires for everything and nix the disconnect box, could I even fit 4 #4 in 1" pvc? The southwire conduit calculator says it can be done with a 38.2% fill but I'm skeptical with my situation.

  • 3
    Get an Ufer ground (concrete encased electrode) in that slab before the concrete truck comes!
    – Ecnerwal
    Oct 7, 2020 at 0:44
  • 1
    Is the existing feeder in pipe (white) or conduit (grey)? That's going to be critical here... Oct 7, 2020 at 1:28
  • I think the grounding plan for this structure is incomplete. You'll want to search for the rules on grounding a separate structure. Additionally, NEC §225.30 forbids you from having two sets of feeders to the shed. You need to consolidate the two feeders into a single set. Oct 7, 2020 at 1:55

2 Answers 2


One circuit or feeder to an outbuilding

If you install a 120/240V split-phase #6 feeder, you have to get rid of the #10 circuit. Then you would feed the well from the subpanel you plan.

The only exception is if a circuit is a different voltage (no luck here), or a different usage - classically, a circuit switched from the source for yard lights, well, etc. If you wanted to do things as you plan, you could always change it so the #10 well line is a switched circuit operated by a pressure switch back at the house.

No elbows -- assemble the conduit then pull the wire

Notice how you couldn't find any PVC conduit elbows and had to steal a plumbing elbow to make that 90? That's because elbows don't exist in conduit. Code requires you assemble the conduit complete empty of wires - and then pull the wires. Can't pull around an elbow. To make turns, either use a sweep, or a conduit body.

Outside disconnect not required

I see you spending some coin to provide an outside disconnect. That's not required.

A disconnect is required for an outbuilding, but it can be indoors. In fact what most people do is choose a "main breaker" subpanel, and use the main breaker as the disconnect. When this is done, the size of the main breaker does not matter. The panel bus+breaker need only be >= the supply breaker.

"But I'm using a main-lug panel that is too small to really have a main breaker!" Um, yeah... about that...

Panel spaces: "Go Big or Go Home" as ThreePhaseEel says.

Nobody ever asked "I need to add a breaker to my panel, but it has lots of extra spaces available. What can I do?" They always ask the other thing.

Painted into a corner because somebody scrimped on a panel, and what was their big savings? At most, a pizza. Spaces are cheap.

For instance in your case, I count 2 wells, a mini-split, and a presumptive need for a 240V circuit for larger tools - that's 4 240V circuits - 8 spaces so far, plus lights and at least 2 more circuits for saw and dust collector. A blink of an eye, and we're up to 11 spaces already - and you picked a 6-space panel which just goes to show how easy it is to short yourself on spaces. So don't make that mistake - select 24-30 spaces and you won't have a worry.

Panels this size also have a distinct, separate main breaker, which creates a better aesthetic than a backfed "main".

Many panels claim "12 spaces 24 circuits" - beware of that claim. The 24 circuits requires use of double-stuff breakers, which precludes use of GFCI or AFCI breakers, which are widely required now. Get 24 actual spaces. They're cheap.

Use a breaker lock instead of well pump disconnects

You don't need a disconnect box for your wells, either.

What you need is a disconnecting means that is either a) in line-of-sight, or b) lockable for lockout-tagout. (NEC 430.102). That way a repairman can be assured that someone thinking about turning on well power will either a) see them, or b) be unable because of a lockout-tagout. The supply circuit breaker is a perfectly acceptable disconnecting means, and that can be a breaker. So the breaker panel could be in line-of-sight (i.e. outside)... or the breaker could be fitted with a locking kit.

Local grounding rods

You need a ground wire for human-made current. But you also need a ground rod for natural current. Code requires the ground rod pass an expensive test, or use 2 ground rods at least 6' apart.

However, since you are making a foundation pour, and surely including some steel re-rod, seize the opportunity to provide yourself one or more Ufer grounds. Turns out, a concrete slab is an absolutely fantastic "grounding rod", and is automatically approved with no testing. You just need to tie into the re-rod at the time of pour. So make sure your concrete guys do that - they should know the drill.

  • I’ll remove the existing and pull a new 4-4-4-8 feed. And I’ll go with a 200amp service panel and nix the outside shutoff. And I’ll also get an 8’ bare copper ground rod in the slab before the pour.
    – D A
    Oct 7, 2020 at 10:25
  • 1
    @DA If there will be any steel re-rod in the pour, then by all means have them provide you an Ufer ground. That is the best ground rod in the world. Never do a pour without Ufers! Oct 7, 2020 at 16:29
  • 1
    And if there isn't add some. Concrete is expensive, steel is cheap, and steel makes concrete so much stronger... An 8 foot rod is not sufficient - you need 20 feet for a concrete encased electrode. So one hunk of full-length rebar is "adequate" but having your rebar properly tied to the rest will involve more than that one hunk of rebar in the system.
    – Ecnerwal
    Oct 7, 2020 at 16:40
  • 1
    @Ecnerwal I think OP was just thinking of a normal copper ground rod set into the ground, installed before pour... yes an Ufer will engage the entire re-rod network. Oct 7, 2020 at 17:08
  • 1
    Pretty much bothering to connect a cable to your rebar, and ideally connect your rebar to the rest of your rebar (which you want to do for structural reasons anyway.) Your concrete and/or rebar suppliers should be familiar with what's needed - I think it's 4AWG cable and a connector suited to the job. Which is why it's something you should always do when pouring concrete - so little extra investment, for the best grounding electrode.
    – Ecnerwal
    Oct 7, 2020 at 23:43

Remove the existing, under the condition you describe you are only allowed a single feeder set to a detached building.

And give yourself a bit of a break on fill and pull a #8 ground, it's good up to 100A.

  • As far as I can tell it’s schedule 80 grey in the ground. I added the white pvc because that’s what I had on hand when I decided to make the temporary setup.
    – D A
    Oct 7, 2020 at 1:44
  • After hearing your comments and giving it a little more thought I think it does make sense to go 3-3-3-6, is pulling 3-3-3-6 difficult through 1”?
    – D A
    Oct 7, 2020 at 1:46
  • 2
    No, I use a fishtape to pull a rope. Then on the wires I strip back 5" of insulation, cut off a little more than 1/2 the strands, then fold remaining strands through the loop on rope folding the ends of the wire to almost meet the trimmed stands, then crimp the fold. After all the wires are through the loop I wrap the from the insulation up to the rope with electrical tape. Oct 10, 2020 at 17:05
  • 2
    If you don''t have a fishtape you can use a shop-vac to suck in kite string or smaller string, with strip(s) of plastic grocery bag tied to the end of the string. Then use string to pull in rope. Oct 10, 2020 at 17:11
  • 1
    I have a steel fishtape and I inserted it at the house panel end. I was only able to get about 75'. So I tried inserting from the pump end. I was only able to get 25' feet. The total length is around 125'. Turns out after a long arduous day of measuring and digging that the previous homeowner or sub didnt glue a connector. And on the 75' block I found an irrigation expander repair coupling mating to another irrigation coupling. I chopped these out and added conduit to replace these blocks and now have a good pull rope sliding smoothly. Just thought I would add this comment for some relief.
    – D A
    Oct 11, 2020 at 14:11

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