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I'm thinking of using an un-conduit-ed SER cable to feed a 100A sub-panel to avoid running 3 separate THHN cables through an EMT conduit (+ maybe a redundant ground).

The panels are 3ft away from each other and the total cable will be 12ft long. I'll be using 3-3-3-5 CU SER cable and running it through the 2 studs in between the panels.

Other specs: The max use load won't exceed 80A. The sub-panel is 225A rated (value pack from a local big store, cheaper then the 12ft SER cable). All of the breakers should be properly rated at the 75deg requirements.

Thx for your input.

Right, perhaps I should better rephrase the question: will I pass inspection if I run a SER cable in between panels without being enclosed in a metal conduit?

I should have mentioned that my current “main” electric panel is actually a sub-panel itself: the proper neutral-ground bonded main panel is outside next to the meter. It has only one 200A breaker feeding the panel in my basement with a SER cable that is not conduit protected.

That’s how I got the idea that I could feed the new sub-panel with a SER without conduit in between. As you can see from the picture my current panel is fed through the ceiling, around the top plate of the unfinished wall and into the first sub-panel without any conduit protection. Then my electrician mentioned that we should add a conduit between the old and the new sub-panel.

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So now I’m wondering if the old SER cable coming from the ceiling should be in a conduit, or If I should add a conduit now.

Alternatively, could I use flexible conduit instead of ridged EMT and pass inspection? Using three #4 insulated AWG THHN cables plus one bare ground cable inside?

Per Manassehkatz’s question: a 2-2-2-4 aluminum SER would be MUCH cheaper but I heard that aluminum SER is more prone to overheating so for $40 more I would rather be playing it safe.

Which contradicts my original question because if I do want to be safer I should enclose everything in a conduit ;)

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  • I presume "un-conduit-ed" means you're not planning on using conduit. That's an... awkward way of saying it.
    – FreeMan
    Mar 1, 2022 at 14:48
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    Any reason you can't use aluminum and save some money?
    – manassehkatz-Moving 2 Codidact
    Mar 1, 2022 at 15:36
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    @FreeMan I think they're talking about the main running inside the wall between the meter and the main panel. That would certainly not pass inspection, since there would be no way to cut the power off of that line. For a subpanel, SER in-wall should be fine
    – Machavity
    Mar 1, 2022 at 16:21
  • As far as Aluminum being more prone to overheating, not if it is sized correctly. Generally speaking (there are tables available with all the details), Aluminum is one size up from Copper for the same amount of power. Yes, heating matters, but the larger size compensates for that.
    – manassehkatz-Moving 2 Codidact
    Mar 1, 2022 at 20:46
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    Yes, you'd use #2Al for 90A or #1Al for 100A. You won't save all that much money going 3 feet, but the lugs are aluminum so I'd prefer it for that reason. @Freeman yes, they are talking about unfused service entrance wire, which is problematic because there is no short-circuit protection at all on it.
    – Harper - Reinstate Monica
    Mar 2, 2022 at 4:45

2 Answers 2

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You can do what you want if you have a 100 amp or smaller feeder breaker in the main. The sub panel will require a 4 wire connection and the non insulated conductor can only be used as a ground. The neutral requires insulation as do the hot conductors, in the sub the neutral needs to be isolated from ground. I make these last statements because you used the term redundant ground.

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  • That seems to be the consensus from different sources. And yes, it will be a non bonded panel. The redundant ground comment: was referring to the fact that if you use metal conduit in-between panels that would count as a ground, making the bare cable ground redundant. THX
    – Marco
    Mar 1, 2022 at 20:43
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Final verdict: After speaking directly with the city inspector, as long as it is not a commercial dwelling, I can use an insulated and jacketed service entrance cable (like the gray coming out of my ceiling in the picture) without protecting it with any conduit inside or outside a wall.

And yes I got a hold of aluminum 2-2-2-4 SER much cheaper and actually available. All of the copper are 3-4 months out. THX for everyone input.

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  • You'll want 1-1-1-3 instead of 2-2-2-4 for a full 100A subpanel -- 2-2-2-4 is only good for 90A unless its feeding an entire dwelling unit
    – ThreePhaseEel
    Mar 10, 2022 at 5:02

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