Cabin Wiring Plan Revisited

Question

OK, So I’ve update my wiring plan … see images. I have more details now, such a part numbers, specifications and ratings, etc. I’ve consolidated much input from a couple of forums as well as Stack, and tried to achieve a synthesis of everything that sounds right, from people who have good ratings and seem to know what they’re talking about.

So, out of the meter we come into a 200A main breaker load center, Square D part number HOM816M200PFTRB. The neutral is bonded to ground bar ONLY EVER at this panel. From the panels ground bar we ground to the PoCo’s ground wire running down the pole, which is a #6 or #4 AWG bare copper wire using a Burndy split bolt part number KS22BAG1R.

Although the panel had feed thru lugs, I decided to go ahead and get a 100A breaker for the house run, because the actual cables themselves are only rated for 100A @60deg C (assume worst case) and it didn’t seem right to hook them to a 200A bus. However the feed thru lugs are there if I need them. We also have a GFCI breaker with 12/2+G UF running about 25 ft to a standard receptacle in a weatherproof enclosure. This seemed more of a correct “hierarchical” solution that people seemed to suggest was better.

For the lateral run to the house the PoCo has supplied me with 1/0-1/0-2 direct burial Aluminum cable. I also wanted a ground to the house, so I ordered a stretch of Mercer 4 AWG Single Aluminum Conductor 600V URD to serve as the ground wire back to the main panel. I was informed by my trenching contractor that gophers are a huge problem and that I had darned well better use conduit. The PoCo confirms this. So all 4 of these conductors are going into 2” Sch80 PVC, and using sweeps at both ends to smoothly bring the cable up. This all goes in a trench 24 inches deep. I do not plan to glue the PVC.

At the house (very small really, 16x24 feet) we have a 100A main breaker panel, square D part number HOM2040M100PC1AVP, neutral NOT bonded to ground. From here we connect to 2 ground rods buried horizontally 24 inches deep in trenches 6 feet apart. The rocks are terrible and it is almost impossible to get below 24” if that. The local electrician said that is what all the electricians do out there. I’ll try to get them to 30” but I can only do the best I can.

Finally out of the house panel we will run, from a GFCI 20A breaker, 10/2+G UF to the shed which will have a light and a 20A receptacle.

IN THE FUTURE (months): I will be wanting to hook up a Reliance 3006HDK generator transfer switch to a genset with a bonded neutral to the house panel

As before (and always) your guidance, criticism and perfect honesty are greatly appreciated.

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Final Changes

• Swap out the pole panel’s 200A main breaker for a 100A main breaker, Square D part number QOM2100VH. And move the house cables to the feed-thru lugs.
• The ground cable is going inside the conduit, I misdrew that, sorry
• Install a ground rod at the pole .. leave the PoCo’s alone (even though the rep said it was okay)
• Find some way to get those dang rods 36” deep, or hire a doggone drilling rig to get a 8 foot bore hole. and also maybe lay a stretch of bare wire in that trench. I’m not kidding, guys … it’s that bad. I don’t think I can do the concrete ufer thing, concrete out there is gonna be tough, and I really don't have an application for the concrete, at least not yet.
• LOSE THE HOKEY POKEY TRANSFER SWITCH. Thank goodness, I see the light. I’m going to go with the interlock option. Square D part number HOMCRBGK1C, which I have confirmed is correct for my load center which is HOM2040M100PCVP. This should provide a code-compliant physical barrier to goofing it up.
• I have a confession. I jumped the gun a couple weeks ago and have already installed the panel in the house, that’s why it ain’t coming out. I throw myself on the mercy of the forum :-O And I swear there will never be enough load at that place to go over 20 spaces. Seriously. No way. It’s just a weekend getaway.
• I’m going to go ahead and glue the PVC but I’m going to skinny the pipe onto the cables before I glue it up.

Thanks for any further comments and your patience with me so far. You guys have been really terrific.

Answer 1

That generator interlock

Don't even think of getting one of those hokey generator interlocks with the 6-10 switches. No reputable electrical switching vendor will make them (ever see an Eaton, Square D, GE or Siemens version? Nope!) At best they're designed for when you can't design the interlock into the system because you did it as an afterthought.

Since this is a blank-sheet design, there are much, much better, simpler ways to do generator interlocks at 1/3 the price, and that let you put any circuit on generator.

The panel size is deceptive, that's 20-space not 40. The "40" claim requires cheater breakers which are illegal on most circuits, as they require full-size AFCI or GFCI.

We'll solve all these problems in a single lick.

The crux is this OEM interlock ($23). It lets us put two Siemens breakers back-to-back ($40 and $10). One is your utility 100A breaker and the other is your generator 60A(?) breaker. These go in the top 4 spaces in a main lug or no-lug panel. Since this steals 4 spaces, we'll bump to this 30-space panel ($66) so we have 26 spaces remaining.

Other vendors make a similar setup, so if you want to shop around, have at.

But this one is Siemens PL, commercial grade -- it even has 2 neutral and 2 ground bars, you don't need to buy them. It doesn't have the bonus breakers so you'll have to replace those. All in all it's about $100 more than your panel choice but it includes a gen interlock that lets you put any circuit on generator instead of just 5. Far easier to wire and there's no question of quality.

Once these 2 top breakers are put in, nothing further need be done with any circuit to make it work on gen - just wire every circuit normally. Even the AFCIs and GFCIs will work properly. When you shut off utility and turn on gen, any circuit you then turn on will feed off gen. Couldn't be easier.

Also, this panel is 125A-ready in case you want to max out your feeder wires.

Other stuff

You didn't mention upsizing the pole breaker to 200A. Feeder lugs there are pointless unless you also upsize the cable to 200A capacity or Aluminum 4/0. "Didn't seem right" - A 200A breaker can't even begin to protect a 1/0 cable let alone a #2. These things can't be left to Providence, that's why we have a Code.

The 1/0 - 1/0 - 2 cable will work fine. #2 is sufficient for 100A under table 310.15(B)(7), and the 1/0 is a bonus hedge against voltage drop. I've been looking for a code cite that allows reducing neutral size, haven't found it, but if it ever turns up, you can kick up to 125A. It's not a service lateral, it's a feeder, and I did find a clause at paragraph 310.15(B)(7) that says you can use the service lateral ratings for feeder that serves the purpose of a lateral.

Conduit

The conduit is a good idea - you'll thank yourself later. Now, you need 18" of earth above the top of the PVC conduit. So if you have to fight for every inch of depth, stop at 21", the pipe is no taller than 3".

Given that you are running in conduit, using cable is wasted and THWN-2 single-conductor is the preferred choice. Cable is legal, it'll just be rather stiff to pull.

I wouldn't glue the PVC either, I assume all outdoor conduit is 100% full of water always, and let the wire's outdoor/wet rating do its job. However watch out for this: Pulling cable will involve a lot of energy, and you could pull the conduit apart in the process. I would leave the ends of the trench unburied so you can quickly fix any pull-aparts. You don't want a pull-apart inaccessible, that will rip up the cable. Ouch.

So here's what we got.

Notice how the utility & gen breakers fit up, easypeasy. After that, I liked your original GFCI MWBC out to the shed, so I put it back in, you don't have to do it obviously. I also show neutral wiring on breakers. I don't show grounds in shed, you know what to do.

Updated with TPeel's main lug feed. If you want the old version hit "edited" just below and look at past edits.

Answer 2

Put your own ground in at the pole

Tapping the PoCo's ground conductor like that is probably a good way to get on bad terms with the power company, who sound like pretty swell folks so far. Instead, I'd use a 6AWG copper wire of my own to my own ground rod driven 8' into the ground at the pole (or some other sort of ground electrode, depending on what soil conditions around the pole are like).

Busbar ampacity does not matter, but your setup doesn't fix what was wrong with the original outside panel

The idea behind the outside panel I recommended was that you fit it with a 100A main breaker (QOM2100) and then use the subfeed lugs for the feeder conductor. Provided the correct main breaker is installed, the busbar ampacity simply needs to be sufficient to carry the current -- putting a panel with fatter busbars in is no different than having 10AWG run 75' to carry 20A to a shed due to voltage drop.

Furthermore, your insistence on a 100A panel for the house is penny-wise and utterly pound foolish -- you can't get 100A panels with more than 20-24 slots, as you probably observed, while a good 200A panel will have three times as many slots (yes, 60 slot 200A panels exist). Having to replace a panel because you didn't provision enough slots for expansion originally is an all-too-common story on this Stack, so that's why we recommend going big on this front.

Use an Ufer ground

If you can pour a bunch of footed concrete with no vapor barrier under it (say for your house's foundation, or for a porch or stoop with a footing even), use an Ufer (concrete-encased) ground in your rocky environment by tying a ground wire to the rebar in the footings and tailing it out before the concrete is poured.

Don't worry about the ampacity of the inside main breaker

The inside panel's main breaker can be any size 100A or greater, really, as it is simply serving as a disconnecting means (shutoff switch).

Get a better transfer setup

Since you have the feeder coming in already, what you can do is get an isolated neutral, single circuit, 100A manual transfer switch and use that to switch the whole inside panel between feeder and generator. This is a more flexible and easier-to-wire approach than the "select circuit" piece of junk you are proposing.

If a 100A transfer switch is too costly or not available enough, the other option would be to use a generator interlock kit on your indoor panel -- this makes it so you can't turn the main breaker on as the same time as another breaker, usually the one in the top left slot or slots on the panel, that you then connect the generator inlet to. This is much less costly than a full transfer switch, yet still Code-compliant with the proper kit fitted.