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The NEC states that "Underground service-entrance cable (USE) shall not be used under the following conditions or in the following locations:

(1) For interior wiring

(2) For aboveground installations except where USE cable emerges from the ground and is terminated in an enclosure at an outdoor location and the cable is protected in accordance with 300.5(D)

(3) As aerial cable unless it is a multiconductor cable identified for use aboveground and installed as messenger-supported wiring in accordance with 225.10 and Part II of Article 396"

With that being known, would it be safe to run the Dyke cable from outdoor to indoor through conduit? The distance from main breaker to sub panel is 120 feet .

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  • code says the cable must be terminated at an outdoor location (eg exterior junction box) . or used underground. OTOH a basement is indoors, and below grade, but is it underground?
    – Jasen
    Dec 7, 2023 at 2:41
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    Does not matter if it's underground, @Jasen, because interior is forbidden, first.
    – Ecnerwal
    Dec 7, 2023 at 2:43
  • 200A main is irrelevant. 100A is relevant only in that is the maximum. But this type of cable (or more specifically, any 2 AWG aluminum wire) is limited to 90A. So you need to breaker it at 90A or less. Dec 7, 2023 at 2:52

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Points 1 and 2 seem to quite clearly prohibit that.

If you terminated the USE at an exterior junction box, before the run goes interior, and switched to a suitable wiring method (such as THWN or XHHW) that would appear to meet the wording of point 2.

More efficiently, sell off the USE to someone with an appropriate use for it, and buy XHHW or THWN for the whole run, no exterior junction box needed.

To borrow a Harper-ism, avoid the sunk-cost fallacy as you apparently have a lot of unsuitable cable for the job you should be doing with suitable wires.

But Actually

You can't use 2-2-2-4 Aluminum to feed 100A to a sub-panel. You can have a 100A sub-panel, but you can only feed it 90A on 2AWG aluminum. You only get the special exception to allow 100A on it if it's the service entrance, (which is, of course, the job that Underground Service Entrance cable is made for) and that ship sailed when the power company's feeder hit the 200A main breaker outside. Everything after that is a sub-panel.

So really, sell the stuff off and buy suitable wire for the job. If you need more than 90A, that's 1 AWG aluminum.

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  • Ecnerwal I greatly appreciate the time you spent to answer my question, to give some context my father wants to use Dyke cable to the sub panel , I told him that doing so would violate the NEC . I asked because the phrasing in the NEC didn't really make sense to me until you mentioned a junction box being used to another cable (THWN or XHHW) again thanks for the response. And no I don't need more than 100 A .
    – John
    Dec 7, 2023 at 21:13
  • 90A. The feed breaker cannot be larger than 90A, because this is NOT a service entrance, this is a sub-panel. The panel you feed can say 100A or 200A on its breaker (and in many cases a 200A panel make more sense just for having more breaker spaces) but the feed breaker in th main panel supplying it CANNOT be 100A unless you upgrade to 1 AWG Aluminum.
    – Ecnerwal
    Dec 7, 2023 at 23:43

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