All, I need some thoughts on how to hookup my new generator. I am going to use a interlock on my main eaton 200amp panel and back feed through a outside plugin wired to a breaker for the interloc. I have a new 7000 watt running generator can peak to 8500. It is also 240v and i just need it to supply a full 30 amps. I have a 30amp breaker and a 30amp power inlet box already. This is how my house is wired now.

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The pipe is 2" PVC sch 80 and the wires in it are thhn 2-2-2-4 copper to the shed feed by 60amp breaker. Also about 130 cable feet.

Here is where the questions start.

  1. Easiest option is to come out of mail panel to power inlet box up cloae to the house. 10ft from panel. Connect 50-100 foot generator cord and be done. Only questions here are i need to unbond the generator since it is a bonded one. Should be floating netural to connect to house this way right? Also not sure about the 100 foot cord only being 10gauge.

  2. The same as above but varies on where the wire comes out of the main panel. I have one pre punched hole left but is is 2in one but works with adapters but is messy on the extierior of the house. The best way is if i could punch a whole through the back of panel but not sure the rules on that something about bus bars being close.

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  1. Last one would be to run new wires in the same pipe that goes to shed to hookup power inlet at shed. Not sure the wire size for distance yet, the fill capacity on the pipe, code about having in same pipe, or the grounding issues. Would you just connect the ground in the existing one since it already has the ground rods installed there or isolated all the way to main panel like if was on extension cord. This way would be nice and clean no extension cords and could run inside shed. That's a different discussion.

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  • What make/model is said generator? Can you post photos of the panels involved please? – ThreePhaseEel Feb 1 at 2:39
  • Also, a portable generator inside a shed is going to be rather problematic from the perspective of getting CO-laden exhaust out of the shed in anything of a timely fashion. – ThreePhaseEel Feb 1 at 2:53
  • Two more questions so far: I take it you want the generator by the shed to prevent CO from getting into the house, or are you OK with having the generator near the house? Also, are those THHNs in the conduit between the two buildings in a cable or just loose wires in the conduit? – ThreePhaseEel Feb 1 at 3:16
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    Are you sure it's 2-2-2-4 copper? Aside from being hella expensive, you can breaker that at 125A, why is it at 60A? I would tend to expect 2-2-2-4 aluminum, which is fine. – Harper - Reinstate Monica Feb 1 at 3:30
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    The wires are loose THHN 135 feet long. LOL iam sure thats what they are. When i built my large house addition needed 100 feet 100 amp so got a good deal on a 500 foot spool THHN #2 for 400 dollars. Used left over for shed. That way can get a large hot tub with no issues. Had the 60 amp breaker figured why buy larger until needed. There is a 100 amp sub panel in shed. – Rob Feb 1 at 4:15

I would use your plan 3 with some adjustments

Your plan to use the existing 2" PVC conduit to the shed is the soundest plan out of the three you've put forth. Running extension cords long distances is just asking for them to get damaged by things, so plan 1 is out. Furthermore, plan 2 would require you to either field-punch a KO somewhat below where you're describing or use the existing 2" KO, but neither of these are particularly practical places for a conduit to exit based on the outdoor picture shown, with the existing KO being a worse option as it'd force you to route the new conduit over the top of the utility's service duct to get to the shed.

However, there are a few things we need to take into account here. First off is the factor of conduit fill. Fortunately, your 2" schedule 80 PVC supplies 742mm² of fill, and you're only using 74.71*3 + 53.16 = 277.29mm² of that so far, which leaves you with ample space for a set of 3 10AWG THHNs for the generator inlet wiring.

With matters of physical space addressed, we then can move onto the next issue, namely ampacity adjustment, as we now have 4 current-carrying conductors in the conduit versus the 3-conductor case Code ampacity tables are based on. This means that we have to limit the 2AWG THHNs to 80% of the ampacity rating they would otherwise have. However, NEC 310.15(B) lets us base that adjustment on the 90°C rating of THWN-2 wire, vs. having to start with the 75°C rating that we're limited to by the terminating equipment here. As a result, we can use the 130A 90°C rating of 2AWG THWN-2 as our basis here, taking 80% of that to get us 104A. Since your shed subpanel is 100A anyway, and 15-30A circuits aren't affected by ampacity adjustment until you get up to 9 current-carrying conductors due to the way ampacity adjustment interacts with the 240.4(D) small conductor rules, we're all good on this front.

The good news is that since we're dealing with a sub-15kW portable generator here, NEC 702.12(B)(2) exempts us from having to provide a disconnect for the generator feeder at the shed:

(B) Portable Generators 15 kW or Less. Where a portable generator, rated 15 kW or less, is installed using a flanged inlet or other cord- and plug-type connection, a disconnecting means shall not be required where ungrounded conductors serve or pass through a building or structure.

So, you can simply run a 10/3 cable out the back of the generator inlet box and into the shed subpanel, where it connects with the aforementioned 10AWG THHN feeder wires in the house-to-shed conduit.

Once you get the feeder back to the house, though...

The more significant divergence, though, comes when your generator feeder makes it back to the house. Since your generator was designed to be suitable for portable usage, it bonds its neutral wire to the generator frame. This is fine and dandy provided it's being used as a standalone source of power; however, it means you can't use it with a normal breaker interlock, as doing so would cause a case of Two Neutral-to-Ground-Bonds Bickering, with potentially deleterious results.

Instead, you need to use a transfer means that switches the neutral, and that limits your options severely. If you wish to stay in Eaton CH, Eaton thankfully makes switching neutral transfer panels (CH10GEN5030SN), but those are limited to 10 spaces for branch breakers, and are relatively pricey/scarce on the ground. The alternative would be to use a Reliance Controls Panel/Link X series transfer panel; these are available in 10-space models as well (XRK0503C/D), and support a variety of 1" breakers (QP, MP, HOM, BR) in addition to being a bit less pricey than the Eaton panels, but are also in limited supply due to a recent model/design change. With either solution, though, you can use the transfer panel to feed a downstream main lug subpanel using either a subfeed block or the transfer panel's own main lugs; this also opens you up to using a panel with fewer spaces of its own, such as the XRH0503D, which might be less expensive than getting the spaces in the transfer panel.

If you want to kit something together yourself instead of buying a premade panel, your options are even more limited: Square-D discontinued most of their switching neutral breakers, BR switching neutrals are too double-stuff-ish to work with interlock kits, Siemens doesn't make 30A switching neutral breakers for their loadcenters to begin with, and GE doesn't make branch-breaker to branch-breaker interlocks for their panels. While Eaton does make CH switching neutral breakers and an interlock (CHML) that fits them, they don't make a suitable retainer for such a setup as the CHPHD can only be used with the uppermost breaker positions. You might be able to use a CHPMIKCH cover-mount interlock kit, but I'm not sure how the retainers for those work, either.

  • Thanks for the through answer. A few things please. I was tracking with you on all the first part up to the end. Two questions on that part. Are the 10awg feeder wires ok that size over 130ft lenghth in the 2 in pipe and still carry 30amp rating? Also there is no ground wire? So just HOT-HOT-NET. Do you hook up the fourth wire ground from the generator to the ground rods at the shed? – Rob Feb 3 at 1:30
  • The generator i got i was going to unbond the netural from the ground. Its in the manual how to do that. Wont that solve this issue? – Rob Feb 3 at 1:31
  • Again thanks for the help. – Rob Feb 3 at 1:31
  • @Rob -- the equipment ground is already taken care of by the existing 4AWG so there's no need to pull another ground for the second feeder. The generator grounding wire does get hooked up to the panel ground bars and thus to the shed ground rods as well as the feeder grounding wire, though – ThreePhaseEel Feb 3 at 1:52
  • @Rob -- you could unbond the neutral from the ground, yes, but you'd have to relabel the generator at that point, and you'd have to undo the mod to use it as a portable – ThreePhaseEel Feb 3 at 1:52

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