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I need to bring a 1/0-1/0-1/0-2 AL SE cable from a 2x4 wall into the back of the main service panel (it is a new subpanel feeder).

The main service panel is surface-mounted on the outsde, on the siding. The wall is 2x4, wood T111 siding, drywall inside (garage) and can be exposed/accessed easly from inside.

It seems the 3.5" of space in the wall is rather tight for the 1/0 AL NM cable to bend.

  1. is it possible (to code) for the cable thickness to fulfill minimum band radius (MBR)?

  2. what fittings to use? (do they need to be liquid tight as the connection to the panel is kinda on the outside (well...panel-on-siding wall but there is no waterproofing there)?

  3. any ideas and advices to solve this problem?

I was thinking about using a conduit right angle fitting to ease the bend (strip the outside sheathing from the SER to ease MBR, after it enters the fitting) but not sure if code/inspector/sanity allows it and how to secure the cable to the fitting?

The new cable is labeled: ALUMAFLEX AA8178 TYPE SE STYLE SER TYPE XHHW-2 CDRS 600V

BTW, There is already an existing, in-service sub panel feeder which enters from the rear via a regular NM clamp connector. The old cable is "thinner" so the bend was easier (though still 100A breaker). This must have been inspected as it was installed when new 200A service was installed so a non liquid-tight was ok?

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  • Pictures always help with something like this..... you've been staring at it for awhile but all we have is your description...
    – JACK
    May 1 '21 at 22:33
  • Yes, pictures definitely help, also your cable is a SER cable, NOT a NM cable! May 1 '21 at 23:02
  • I don’t have time right now but if it’s nm cable you have to enter from the back in most states as NM is not allowed outside by the NEC, you can not strip the NM the covering is required to enter the box 1/4” minimum. Providing your location would be helpful as different states are on different code versions.
    – Ed Beal
    May 1 '21 at 23:11
  • Is having a box on the inside of the garage wall an option? P.S. according to the Southwire spec sheet for your cable, it's 1.168" in diameter, nominal. May 1 '21 at 23:55
  • That would require a 5.840" bending radius. May 2 '21 at 1:58
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On a seemingly unrelated topic, I like to see houses have LOTS of spare breaker panel spaces. Spaces are cheap, and in the future stuff always comes up, and nobody has ever posted "Help, I want to add an RV outlet, but my panel has 18 spaces available. How can I squeeze it in?"

Hold that thought.

Now, given the thickness of the cable, I do not see way to make that bend. What I advise doing is installing a LARGE junction box on the inside of the garage wall. Now your SE-R cable can enter that box vertically, transition into individual wires, and go through a conduit nipple from this inside box to the outside box. At that point we're only concerned with radius of individual wires, and that's no problem.

Now let's price that. Splices of large wires require very long, tall boxes. We also need splice connectors for 1/0 wire (four of them)... Hold on a minute. What's a LARGE box that comes with big lug connectors, that's cheap?

Why a subpanel, of course!

So if extra breaker spaces wouldn't be useless, the best answer may be to fit a large subpanel on the interior of the garage. "Large" because you want full width, and enough height to handle the large wire bends.

And that's exactly what I'd do. Select a 200A-bussed, main-lug but convertible subpanel of 20+ actual spaces (not circuits).

I'd arrange the new panel back-to-back with the existing panel, using a "nipple" to connect them that is as large as the knockouts allow.

Downhill from there.

If the SE-R cable's internal conductors have their own markings (as XHHW conductors) then you can enter the new subpanel with a grommet/cable clamp, then pass right through the new sub and into the original panel - at that point you're just using the sub as a giant junction box.

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  • I love that idea. I suppose I can put a smaller subpannel on the opposite side in the garrage. Wire it to a 100A to the main (even use short Cu wires) and than cascade to my new (necessarely more remote) subpannel. And get few spaces for garage utills and 50A EV charger. Briliant.
    – Michal
    May 2 '21 at 6:52
  • One more Q: there are no knockouts on the back of the main pannel. The existing entry seem to have been cut manually?
    – Michal
    May 2 '21 at 7:01
  • Yes, you can drill your own KO. Get as many subpanel spaces as you want, sky's the limit. 125A is the practical limit before it gets hard to get main panel breakers. That is #1 Cu for an honest full 125A. I recommend a 200A bussed panel that is convertible to main breaker. That way if you ever "heavy up" your service to 200A, it would reduce the cost — you just flip it so this panel is the main, and the outside panel becomes the sub. May 2 '21 at 16:52
  • "A 14" wide psubpane gives you" Gives me WHAT???? And what's a "psubpane"??? :D BTW- Your story-telling style of writing answers is really quite effective.
    – FreeMan
    Sep 29 '21 at 12:43
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    The back-to-back subpanel is a rather clever solution to this issue indeed! Sep 30 '21 at 1:16

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