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I ran out of space in my "main" (sub)panel (A siemens PN4040B1200C) (my real main panel is the meter-main combo on the exterior of my house), so I'm trying to install another subpanel next to it. I got a Siemens PN panel (PN3048L1200C to be precise -- 30/42 space, 200 amp main lug panel). I also had some extra 4/0 SER lying around as well as a 200A branch breaker (QN2200RH), so I figured I'd just feed the entire 200 amps over even though I realize it's overkill. However, I realized that Siemens doesn't seem to make a main lug kit that fits my 4/0 neutral wire. They make an ECLK3 lug kit, but I don't think that fits onto my neutral bar.

So:

  • Should I just buy a length of 1/0 SER instead and feed it off of a 125A breaker? The neutral would then fit in a ECLK2 lug kit.
  • Also: why is the subfeed lug kit (ECLK2225) so expensive? It costs more than the 200A branch breaker! enter image description here
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  • Something doesn't add up here.. can you post pics of everything you've got? Including the meter-main combo on the exterior of the house? Jun 29, 2022 at 4:49
  • Sorry, my phone camera's busted right now. In lieu of that, hopefully this diagram works for you... the gist of the question is there doesn't seem be a lug kit that fits that 4/0 neutral.
    – atanamir
    Jun 29, 2022 at 5:00
  • Please revise your post title to as a single clear, specific question. If you can't easily do that you may be asking too much in one post.
    – isherwood
    Jun 29, 2022 at 13:11
  • Going with that large of a sub feed takes ganged set of breakers on most panels this is why it is so expensive. Something that is not often done so lack of volume or “specialized “ parts get expensive.
    – Ed Beal
    Jun 29, 2022 at 20:42

2 Answers 2

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Not only should you interconnect the panels with conduit (better than cable)... you should interconnect them with a number of conduits for convenience of pass-thru. You'll thank me later - I guarantee it!

Drill right through the studs. For the large pipe (1-1/2 or 2") I would use RMC the right length, with conduit nuts on the outside only. That way the hole doesn't need to be any bigger than the RMC. This is not good enough to carry ground, so run a ground wire.

Siemens designs their knockouts to a standard pattern, so KOs on any Siemens panel will line up with KOs on any other. Make cross-connections using conduit nipples or RMC conduit.

Make a 2" pipe for the feeder, and as many 3/4" cross-connections as you are willing to do, for future use by branch circuits.

If you are able to use 4/0 hots and 2/0 neutral, then you only need 1-1/2" conduit for the feeder.

Both hots and neutral must go through the same conduit. Ground can go another path, which is how you can make it work in 1-1/2" conduit.

You can run the whole SER through 2" conduit, or if the individual wires inside the SER have markings identifying their insulation type, they can be shucked out of the sheath and used as they are. Or you can use THHN or XHHW individual conductors.

Any branch circuit can be moved to the other panel as simple as moving its hot(s) and neutral via a 3/4" cross connection - the safety ground can stay in the panel the cable enters. Wires can be extended with wire nuts. They're allowed in the feeder cross-connection (space allowing), but I recommend several at least near top and bottom so you have the best chance of the existing wires reaching into the other panel to the new breaker.

As far as getting a 2/0 neutral connection, once we get you out of "fat cable" and into "individual conductors", you can simply use 2/0 copper for the neutral wire. It's only a few feet. Copper is perfectly safe at these large feeder sizes :)

I don't normally go around "spending your money", but in this case it's worth it for a few feet of 4/0AL and 2/0Cu and a much cleaner, pro tier installation that will be easy to manage and maintain (with all those pass-thrus).


Note that 4/0 is only legal for 200A if your entire service is 200A due to the 310.15(B)(7) exception. If this is half a 400A service, the exception does not apply, and 250 kcmil is required. (or #3/0 copper).

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  • Harper could you show me where conduit is specified over cable? It is not even conduit regularly is required to be bonded to the box especially if tko or knockouts are used a wire is still required metallic conduit is not required.
    – Ed Beal
    Jun 30, 2022 at 20:35
  • @Ed Sorry did not mean to suggest cable was not allowed. Jul 1, 2022 at 2:23
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A 4/0 neutral is very unusual. Almost all services are two 4/0 hots and one 2/0 neutral which is probably why you can't find a bus bar with lugs that fit.

That said, since this is a sub-panel, you must isolate the neutral from the ground, in common parlance "float the neutral". Since it's such a short distance you should consider simply connecting the sub-panel and main panel with a short length of conduit and getting the appropriately sized THHN/THWN wires. Because copper is much easier to to work with than AL and you won't need much of it, I'd go that route. If you really wanted to go the full 200 Amps that would be 3/0 and 1/0 in copper. You'll also need a separate ground (#4 copper would work) to complete your true 4 wire service to the sub. Just saying again, you must isolate the neutral from the ground in your sub.

You might consider what loads you are running in the sub-panel and size the breaker and wiring for it. It might save you some money.

Lastly, I bristle at using parts you have "laying around" instead of getting the appropriate parts for the project. But that's just being grumpy.

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  • Copper of the same ampacity as aluminum is actually slightly harder to work. Copper is a stiffer metal than aluminum, and even being +2 wire sizes smaller doesn't make up for it. Jun 29, 2022 at 19:55

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