I have about a 180' run from my house's main panel to my shed. I've installed a SquareD Homeline 70A sub-panel which has no main breaker, and has two breakers within.

I have installed a ground bar in the sub-panel and connected it to a ground rod at the shed. I have wired the circuit (one for now) with the neutral to the neutral bar and the ground to the ground bar (neutral and ground are not bonded).

I'm looking to clarify a few final things before I complete the installation. Sorry for all the words. I've highlighted the important parts.

  1. I've seen conflicting information regarding whether or not I need to run a ground from the main panel to the sub-panel and bond it to the sub-panel's ground bar. Is a ground from the main panel required or is the ground rod at the site enough?
  2. The run is 180' and the sub-panel is rated for 70A. I was going to run 4AWG 3 conductor (plus ground if required). I may go with 1AWG in case I want to upgrade to 100A service at the shed in the future. Using separate THHN wires, not UFB. Sound good / suggestions?
  3. If I run 4AWG, and ground is required, what size ground would I use? What if I run 1AWG?
  4. I am planning on running the wire in schedule 40 conduit. I think I should run 3/4" conduit if I go with 4AWG, or 1" conduit if I go with 1AWG -- probably might as well run 1" regardless. Sound reasonable?
  5. Since the sub-panel has no main breaker (again, it has two beaker slots), do I need a disconnect before the sub-panel?
  6. I will be using GFCI / AFCI breakers for both circuits, so do not need to use any GFCI outlets -- correct?

Anything I'm missing?

Update / TLDR

  1. Run ground from main panel; use 2 ground rods at sub-panel, 10' apart.
  2. For 100A @ 180', use aluminum XHHW-2 1/0 1/0 1/0 2.
  3. Aluminum XHHW-2 2AWG for 100A @ 180'.
  4. Use Schedule 80, 1 1/2" (33% fill) or size up to 2".
  5. No disconnect is needed for a panel with only 2 breakers, however, it would be wise to upgrade the sub-panel to include a main breaker and more breaker slots.
  6. GFCI breakers, no GFCI outlets.
  • 1
    Welcome to StackExchange. Honestly I had to hold myself back from believing you are trolling us, since in this question you've managed to stack up every newbie mistake a person can possibly make with a subpanel, except laying the wrong wire and then covering it up. *What's worrisome about this is apparently the source of your information is really, really, really bad; and it raises questions about what *other mistakes are afoot. I strongly advise asking more questions about every step of the process. – Harper Apr 26 at 13:42
  • @Harper -- please elaborate and help me do it right. I've done a lot of research and honestly thought my assumptions were correct. Not trolling. – Josh M. Apr 26 at 13:52
  • OK thanks for bearing with. Fasten your seat belt :) – Harper Apr 26 at 13:55
  • @Harper -- I'm waiting patiently. :) – Josh M. Apr 26 at 14:16
  • You don't plan to use GFCI protection for receptacles? Better read up NEC 210.8.A.2. Garages and accessory buildings on grade All receptacles require GFCI protection there are no exceptions unless your state has some like mine has for freezers. – Ed Beal Apr 26 at 19:44

There are so many mistakes here that I'm very concerned about the fact-finding process which led to them (or lack thereof). Because "writing a book" is not the SE format here, I'll be lightly touching on each.

But speaking of "books", and going back to that fact-finding process, I'd strongly advise hitting the library for some reasonably current books on electrical, and read them through - the goal being to get a well-rounded primer on the subject. Google gives you swiss-cheese knowledge because it only asks questions, and without a primer you don't know which questions to ask. Home-improvement store clerks know worse than nothing.

Anyway on to it.

Voltage drop - the first question on a 180' run. Here I deviate from stock advice, which is keep rigidly <3% of breaker trip. Actually, 3% isn't in Code anywhere, and it's a very coarse rule of thumb - 5% isn't wrong. And you should be computing voltage drop based on practical loads, i.e. what you expect to be actually pulling on a regular basis.

Aluminum wire - you didn't mention aluminum but you should be using it for large feeder >=4AWG. That means a size bump from copper. I often see people take dangerous shortcuts to save $30 on a project only to spend $800 more than they needed to because they're afraid of aluminum. Aluminum didn't work for small wires like #12 using alloys made for high tension lines. Feeders were always reliable in that alloy, and they've improved the alloy too.

The service panel. Everybody does it the first time. First get a huge panel - when you're buying a panel, spaces are cheap. Regrets, however, are expensive - and believe me when the power is there, you'll want to use it. 240V heaters, on-demand hot water (30A/240V is fine), electric car, prosumer shop tools that are 240V, these things chomp up breaker spaces 2 at a time. A 30-space breaker is only 15 loads. A 42-space is not uncalled for.

Honestly a 70A subpanel that's only 2 spaces makes no sense as a product. It could only serve as a shutoff switch for one single 30-70A machine. It is wholly inappropriate to power a variety of circuits, as it sounds like you want in this shop.

Second, you need a "main breaker" because that's your shutoff switch/disconnect (5). The most economical way to buy a disconnect is simply select a panel with a main breaker. Amp rating? Nobody cares, it's a disconnect. So feel free to get a subpanel with a 150/200A main breaker if that'll give you a sensible number of spaces.

For aesthetic reasons, I strongly prefer panels with an obvious, separate main breaker/disconnect, not one where the main is in the rows of regular breakers and only found with a "main" label. I want a visitor to be able to find the shutoff in a hurry, in half-light, in smoke.

Separate Ground bar - correct. Neutral-ground isolated - correct.

Ground rod (1) - unless you've done the arcane wizard measurement to affirm <25 ohms on the ground rod, you need two rods some distance (10'?) apart, unless your local code says otherwise. Code often has local amendments based on local conditions.

Ground wire - the only conflicting information there is "All the Codes say this is required" conflicting with "I don't want (you) to pay for it" (because I want to quote you a better price than my competitor, who is following the law). You need a wired ground wire back to the house. Period. Dirt doesn't conduct electricity well enough to serve as a substitute, if it did, we would just put THHN insulation jackets on dirt.

Ground size bump vs. voltage-drop size bump (3). When you make wires bigger for voltage drop, you must make the ground wire bigger in proportion to cross-section. That math sounds hard, until you realize wire gauge already works that way. So if you do a +2 AWG size bump for voltage drop, simply do a +2 AWG size bump for the ground also.

THHN wires inside conduit (2) - correct. You use THWN-2 wires inside conduit. (almost all THHN wire is dual-rated THWN-2, so people don't bother distinguishing them).

Don't push the limits of conduit fill. (4) Those limits are intended for pro electricians with experience, special pulling hardware, lube, and a winch on their truck. As a novice doing your own pull, be generous with conduit size, or else you could find yourself boxed into a corner and having to bring out an electrician to finish. In this economy electricians are not hungry, and won't return your calls unless you give them most of the job (and let them bill for that). Also if there are any defects in your work so far, they won't touch the job with a 10 foot pole unless you hire them to fix it all. So pencil in $1000+ for that.

No need for GFCIs downline of GFCIs (6) unless you want to play a "Yo Dawg" joke on yourself. There's no penalty for doing so; it's just wasteful.

  • Thank you. I'm not sure if I was unclear or not (my question wasn't intended to indicate exactly what I planned to do, but what I had read vs, what I thought was correct) but everything you said here matches with my assumptions in my head other than copper vs. aluminum (I didn't know I should use aluminum). I will use a panel with more spaces and a main breaker. I will not (and was not intending to) use GFCIs + AFCI/GFCI breaker, just wanted to confirm! Will add a second ground rod. Will run ground from main panel as I expected. – Josh M. Apr 26 at 16:01
  • Also, to be clear, this is all to get some lighting to my two sheds, some LED yard lighting and a couple aux outlets. Also a small pool filter. But down the road one shed may be replaced with a proper shop, so I wanted to make sure I had enough overhead in the feeders to support that w/out re-running wires. – Josh M. Apr 26 at 16:04
  • (I've added a TLDR to the OP for clarity.) – Josh M. Apr 26 at 16:51
  • 5. You DO need a disconnect with a panel with 2 breakers. You only don't need a disconnect if there's 1 (e.g. 2-pole) breaker, since at that point the breaker and the disconnect become indistinguishable. And 1 2-pole breaker can feed 2 120V branch circuits (except there's no such thing as a 120V/70A branch circuit). However, in that case, how do you expect to attach branch circuits? You cannot put a 20A receptacle on a 70A breaker. I think there's a gigantic, enormous, hole in your knowledge here! Maybe you should explain what circuits or loads you aim to attach. – Harper Apr 26 at 17:07
  • Regarding #5, you say a disconnect is required for my current 2-breaker sub-panel. My understanding of NEC 225.31-33 is that I do not need a separate disconnect since a) my sub-panel is installed on the outside of the she and is the service entrance (I realize i did not mention this prior) and has 6 or less (2) breakers in the same enclosure. However I will be upgrading the sub-panel anyway, as you suggested. – Josh M. Apr 26 at 17:44

1: Lacking a time machine to go back several decades, a grounding wire is required. That requirement was added several decades ago because the lack of one causes real problems.

2: see harper's answer which got finished before I finished this one, though it looks to me like you already chose but did not state aluminum based on your stated sizes. 2 & 6 (or 1 & 4 if you love the under 3% rule - or compare costs.) Having had issues with things like compressors starting at the end of inadequate feeds, if cost is not too great I personally like to bump it up. Do what you like.

3: 6 alu minimum for 61-100 amps. But bump to 4 if bumping reasonably.

4: Use schedule 80, upsize it from the bare minimum. Max fill is a huge pain to pull for very little cost savings. Schedule 80 costs very little more for a significantly tougher conduit, and you probably require schedule 80 at the ends for prevention of damage aboveground anyway. You need 1-1/2 minimum for 3x2AWG + 1x6AWG, I would strongly suggest putting in 2" and considering a spare, capped, smaller conduit for any potential communications need in the future - conduit is cheap, trenches are expensive. Hit up an electrical supply house and get 20 foot chunks of schedule 80 (they probably deliver) - what's in stock at home cheapo is not a good metric, and also isn't all that cheap on this front, as I recall the comparison when I did most of this work. Use long (large radius) sweeps (you may think they are elbows) on the ends where you need to come out of the ground. If you get frost, and perhaps even if you don't an expansion joint at each end is useful so the conduit can move relative to the building (vertically) without breaking.

5: if it can be shut off in 6 motions of the hand, no. If not, yes. If there are more (currently unused) spaces in this panel, how many are there if you used them all? If there are not more spaces, just return it and get a main breaker panel, they can be shockingly inexpensive and are much more useful in general.

6: correct.

  • Thank you. I've combined your and Harper's info into a TLDR added to the OP. for clarity. – Josh M. Apr 26 at 16:51
  • You might be underestimating allowable wire sizes. For <=99A you need to pull out of the 60C column of 310.15b16. – Harper Apr 26 at 18:02
  • @Harper -- I'm planning for 100A @ 180' using 3 conductor 1/0AWG aluminum XHHW-2 and 2AWG ground. – Josh M. Apr 26 at 18:13
  • 1
    @JoshM oh, that's fine, it's just the right amount of overkill to let you solidly pull 100A without any voltage drop worry. I was concerned with this answer's 100A on #2AL, that's been a wobbler in my mind, I'm don't think it's right but I can't say why it's wrong. It's fine for service because of 310.16b7, but I don't think that applies to feeder. – Harper Apr 26 at 18:24

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