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I need to install a 240V 40A circuit into my garage. The end goal is to plug in a level 2 EVSE. (maybe it can be a 50A circuit? not sure).

I have an existing 50A GFCI breaker hooked up to 6 gauge 3 wire aluminum (labeled as 6 AL on the romex). The aluminum romex extends from the breaker through my basement outside underneath the deck. There is no conduit, just the romex stapled underneath the deck. The original intent of this circuit was to power a hottub (that no longer exists). The date on the romex is 1994.

My idea is to res-use as much of this setup as possible but extend it into my attached garage. The circuit would need to be extended from the deck to my garage and then through the siding above the foundation.

1) Can you run romex outside your house and then back in? I would think you would want conduit on the outside. I am not sure this setup is code at this point. 2) Should I be worried about aluminum wiring and the heat stress issues?

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  • Is this actual NM that's stapled under the deck, or UF? – ThreePhaseEel Jan 3 '18 at 3:34
  • Standard romex or nm is not listed for outside use but if UF it would be ok if the splice is in a junction box. Just a note UF is usually gray or black but it will have a label that identifies what it is. – Ed Beal Jan 3 '18 at 9:56
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    The full wire labelling is: "ALCAN S STABILOY (R) AA-8000 AL type SE cable style U XHHW 500 U 3 CDRS 6 AL (UL) 1994" – cshimer Jan 3 '18 at 10:35
  • Are there 3 conductors in the cable and then the concentric "shield" wrapped around the outside, or does that 3 number mean there are only 3 conducting paths through the cable? – ThreePhaseEel Jan 3 '18 at 23:18
  • I am pretty sure this is UF. I haven't actually taken a look at the inside conductors. I should also note that I am primarily doing this as a costing exercise. I am planning to hire a licensed electrician. – cshimer Jan 4 '18 at 2:36
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This is fine for 40A, as long as your EV charger does not require a neutral connection

A 6AWG aluminum wire is rated for 40A on 60°C terminations and 50A on 75°C (really 60°C/75°C) terminations. Your SE style U cable supplies two of these conductors, one for each hot, plus an uninsulated concentric sheath under the jacket that is in all likelihood the equipment grounding conductor (as your average hot tub has no use for a neutral), as permitted by NEC 338.10(B)(2):

(2) Use of Uninsulated Conductor. Type SE service-entrance cable shall be permitted for use where the insulated conductors are used for circuit wiring and the uninsulated conductor is used only for equipment grounding purposes.

Given that SE cable is fine for indoor and outdoor usage as per NEC 338.10(B)(4):

(4) Installation Methods for Branch Circuits and Feeders.

(a) Interior Installations. In addition to the provisions of this article, Type SE service-entrance cable used for interior wiring shall comply with the installation requirements of Part II of Article 334, excluding 334.80.

For Type SE cable with ungrounded conductor sizes 10 AWG and smaller, where installed in thermal insulation, the ampacity shall be in accordance with 60°C (140°F) conductor temperature rating. The maximum conductor temperature rating shall be permitted to be used for ampacity adjustment and correction purposes, if the final derated ampacity does not exceed that for a 60°C (140°F) rated conductor.

Informational Note No. 1: See 310.15(A)(3) for temperature limitation of conductors.

Informational Note No. 2: For the installation of main power feeder conductors in dwelling units refer to 310.15(B)(7).

(b) Exterior Installations. In addition to the provisions of this article, service-entrance cable used for feeders or branch circuits, where installed as exterior wiring, shall be installed in accordance with Part I of Article 225. The cable shall be supported in accordance with 334.30. Type USE cable installed as underground feeder and branch circuit cable shall comply with Part II of Article 340.

, your plan to reuse this for a 32A continuous/40A maximum EVSE seems sound provided the EVSE does not require a neutral (which this cable does not provide), and there is nothing in Code I can find that prohibits an outside branch circuit or feeder from re-entering the structure it originates in. Of course, you will need to use a 40A breaker for this (unless your EVSE has 75°C rated terminations, which will let you keep the existing 50A breaker and run the cable at 50A instead of 40A).

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In answer to your first question. You shouldn't be running type NM under decks without other protection. I refer you to NEC 2014 Article 334.12 Uses not permitted (B)(4) In wet or damp locations. And from the AHJ I have worked with under the deck is a wet or damp location.

The conductor size is fine but I don't like using Aluminum conductors if there is the slightest suggestion that it may be subjected to heavy loads and cause the conductors to overheat like with a motor type load. I am not sure about type 2 EVSE but I would check with the manufacturer to see what they recommend.

I am not sure what you are asking about with your last question. First we have NM cannot be allowed exposed on the exterior of the house, but any approved conductor or cable methods can exit and reenter walls if the proper code requirements are met. These methods are covered in the NEC chapter 300 under the proper Article for each method.

Good luck

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  • This is SE not NM (see the comments under the OP) – ThreePhaseEel May 12 at 1:14
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You can't use #6 aluminum on 50A no matter what scenario ... I'm terrified here that you're not grasping the basic concepts of electricity and you need to hire a professional that is licensed and insured to do this work properly.

You absolutely positively 100% cannot "extend this to the garage" because it's a detached structure and this requires the entire wiring setup to be changed to meet codes. You must install a sub panel in the detached garage and you can't simply re-use the "romex" hot tub wiring for this.

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  • >The full wire labelling is: "ALCAN S STABILOY (R) AA-8000 AL type SE cable style U XHHW 500 U 3 CDRS 6 AL (UL) 1994" That's service entrance cable, you can't use this for anything else and they were violating codes when they installed this hot tub with it. That was likely a horribly dangerous setup with no GFCI and using service entrance called in an unapproved usage. – Bob the builder May 12 at 0:59
  • SE style U with 2 hots and the outer metal braid as a ground is A-OK for a 240V only appliance (no neutral) -- see NEC 338.10(B)(2) – ThreePhaseEel May 12 at 1:16
  • Also, 338.10(B)(4) permits SE cable for feeders and branch circuits – ThreePhaseEel May 12 at 1:29
  • Not sure where you got "horribly dangerous setup with no GFCI" from. OP said existing 50A GFCI breaker. – manassehkatz May 12 at 3:02

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