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I am renovating the 2nd floor of my 1970's home. I decided to change from 1 switched outlet with a lamp in each room to the switch controlling 4-6 LEDs.

Breaker Box: Dual Pole 15 Amp Breaker

Supply Wire: Black Aluminum 12/2

Splice: White Copper Romex 14/2

Wing Connectors: Purple Al/Cu

I was able to find the power leading into the switch from my attic and cut it. The supply to the switch was 12/2 even though the breaker is 15 amp. In the picture you'll see almost all 12/2 out of the breaker box even with various 15 amp breakers. I believe the reason 12/2 was used is because it is a significantly long run. My breaker box is in the garage and the room I'm working on is the farthest room on the 2nd floor. So probably a good 50-60 foot run. I added a junction box in the attic and spliced the 12/2 with 14/2 using al/cu connections and ran the 14/2 to the outlet for constant power and from the switch to the 4 LEDs.

I have attached a picture of my breaker showing 12/2, 2 examples of junction boxes in my attic using 12/2 and 14/2 splices, and the 4 LED's in which I have already installed. Willing to redo if recommended.

I want to continue doing this to all the other rooms but looking for validation that what I'm doing is safe for the long term. Can I continue my project or would I be better served to head to the store and grab some 12/2?

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isherwood
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TL DIY
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    See [this answer](https://diy.stackexchange.com/a/242612/65210) to a similar question. What you are doing is ok in principle. It's a good idea to put labels/notes in the breaker panel to help future maintainers understand the breakers cannot be upgraded to 20A for both reasons, cable length and your changes. – jay613 Feb 01 '22 at 15:53
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    @FreeMan didn't he write that the original wiring for this 15 A circuit was 12/2 aluminum? So no one should think "20 A circuit". Splicing with 14/2 copper is fine and best use of material. However, using the purple wing nuts for an aluminum to copper connection is not recommended by experts. Use AlumiConns at least for line and neutral. Ground wire can be wire nut with antioxidant compound. Burndy Penetrox is reommended. – Jim Stewart Feb 01 '22 at 17:22
  • @JimStewart is 12/2 AL required for a 15A circuit? I wasn't aware of that. However, the advice is still important because many DIYers probably aren't aware of that. – FreeMan Feb 01 '22 at 17:34
  • I assume this must be code. My 1970 tract development has 10 AWG aluminum for 20 A circuits and 12 AWG for 15 A circuits. – Jim Stewart Feb 01 '22 at 17:42
  • I would NOT fasten all these boxes to the tops of the ceiling joists. If you would later want to increase the insulation you want to keep the boxes out of the insulation. If you must fasten the boxes to comply with code, attach by screws an 18" piece of 2x4 to the joist and attach the box to the top of that. Nailing anything onto ceiling joists could damage the drywall ceiling. – Jim Stewart Feb 01 '22 at 18:20
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    @FreeMan yes, the AWG sizes only indicate *physical diameter*. Aluminum being a *very* lightweight metal compared to copper, needs a larger wire diameter of -2 wire sizes. E.G. that's why a 90A feeder is #4Cu / #2AL or 200A service is 4/0AL vs 2/0Cu. (not to suggest anyone should use copper for feeders LOL, someone in pursuit of safety has far more effective ways to spend that money). – Harper - Reinstate Monica Feb 01 '22 at 20:14

2 Answers2

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12/2 aluminum is rated for 15 A only. In houses wired in aluminum 10/2 is used for 20 A circuits.

So in pigtailing or extending aluminum wired circuits 14 AWG copper can be connected to 12 AWG aluminum and 12 AWG copper to 10 AWG aluminum.

Purple wire nuts are not recommended by experts. The experts recommend AlumiConns. AFIK three port AlumiConns only allow up to three wires, one wire in each port. I usually use two port AlumiConns when I have only two wires, but sometimes use three port AlumiConns and leave one port open for future splicing.

If I have four or more wires to connect, I have used a good quality gray wire nut (Scotchlok is what I have used preferentially) preloaded with Penetrox. I use emery cloth with Penetrox on the cloth to abrade each aluminum wire before inserting the set of wires into the wire nut.

When I pigtailed our 1970 house in 1980 I generally followed the procedures of electrical engineer Jesse Aronstein formulated in collaboration with CPSC.gov for pigtailing aluminum house wiring. The one thing I did not do was to strip the wires long and pretwist the set of wires to be connected, then cut off the twisted bundle to the correct length for the wire nut. I did not have enough wire. I have not had any failures of the splices I made over 40 years ago.

EDIT

I would NOT fasten all these boxes to the tops of the ceiling joists. If you would later want to increase the insulation you want to keep the boxes out of the insulation. If you must fasten the boxes to comply with code, attach (with screws) an 18" piece of 2x4 to the joist (oriented vertically) and attach the box near the top. Nailing anything onto ceiling joists could damage the drywall ceiling.

Jim Stewart
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    Aluminum wire nuts have not stood the test of time. For four or more wires, try ILSCO's "Mac Block Connector". It is a lug block connector with 2 voids, and each is listed for up to 4 wires of the same kind. So 2AL to 3Cu, etc. – Harper - Reinstate Monica Feb 01 '22 at 19:10
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TLDR: #12 aluminum for 15A is correct. Use lug connectors, not purple wire-nuts. Favor metal boxes.

Wire sizes

The wire sizes are a physical diameter and do not reflect current capacity. #12 aluminum is correct for a 15A circuit. Aluminum is 1/4 the weight of copper, and being so light it needs more volume of wire to carry the same current. By -2 wire sizes as a rule. You have to get used to this.

The thing about aluminum

Look inside your service panel. See the main lugs where power comes in? See the neutral bars and ground bars if present? Notice how they are silver colored. Tin-plated brass, right? No. Tin-plated aluminum.

Aluminum has different thermal expansion than copper. This works in aluminum's favor when it's a lug - making aluminum lugs the "universal donor", working well with both. Copper lugs, on the other hand, do not play nice. This was not well understood when in the 1960s, the copper shortage came on fast, and UL was pressured by government to quickly approve receptacles and switches for aluminum wire. Manufacturers did minor tweaks and UL rubber-stamped it. Mistake.

Since then, this has been fixed (over-fixed?) with the "CO-ALR" rating for switches and receptacles. Check one out sometime: it's not even aluminum, it's a rare-earth metal. You can attach aluminum directly to those and do not need to pigtail.

However, copper wire connections were failing on copper and aluminum lugs. Why? Research in the 2000s turned up that screw torque really matters, even on the little stuff. (Electricians had always torqued the big stuff, note aluminum heavy feeder never had a problem). Testing at trade shows showed electricians couldn't hand-torque any more accurately than their business manger, spouse or lover! So in 2014 NEC was amended to require torque screwdrivers on darn near everything. Mind you, all this is copper, but in the 70s and 80s, nobody was torquing small aluminum connections either. Hmmmm!

All together, this gives us a pretty good road-map for handling aluminum smartly:

  • Use lug connectors whose bodies are made of aluminum (universal donor)
  • Set the torques correctly with an inch-pound wrench.

Purple wire-nuts are not reliable. Use lug connectors.

You need go no farther than Google image search.

But based on the above, that's not really a surprise. The purple twisters are just a minor tweak on regular wire nuts (the very thing that did not work in the 1960s with receptacles). It doesn't manage aluminum's thermal expansion differences, and certainly doesn't leverage it to advantage. There is no way to set its torque properly.

But lug connectors (like Alumiconns) leverage what works: they are lugs made of aluminum (basically your panel's neutral bar, just adding a plastic insulation box). You can torque them to the correct value for more confidence still.

Alumiconns work for 2-3 wires. For 4 or more, use another product: ILSCO's "Mac Block Connector". This has 2 larger holes, but each hole can take 1-4 copper wires, or 1-3 aluminum wires.

The largest such "lug connector" is Polaris, but not useful here (it only takes 1 wire per hole and very costly. Generally used for 4 AWG or larger panel feeder but only in unusual cases.)

By the way, local stores cheaply sell "accessory ground bars" for retrofitting into service panels, which are more of the same - and are rated for typically 2 wires per hole. I'm not saying you should buy long ones and cut them up to make "bare Alumiconns", but see below.

Metal boxes vs. plastic

I gather from the rust on those nails that you're just using old boxes you had lying around. They're not fit for the job, since you don't want to be nailing to a joist with a finished ceiling below it.

If you're going to buy new boxes for that job, buy metal. Why? We use junction boxes for specific reasons. Metal boxes are better at every one of those reasons. It contains arc fires better, it won't burn itself even if heat is applied to it, it contains arcing, and if a hot wire contacts it, it will assure the breaker gets tripped like it's supposed to.

For cable clamps, I just buy the cheapie boxes with knockouts, and use Romex cable clamps designed to go into those knockout holes. They're cheap. If you want built-in Romex clamps without high cost or wacky mounting flanges, you have to shop a little, especially since big-box stores do not carry good selection even on a good year. But my mainstay box is a basic 99 cent 4x4x1-1/2" drawn steel box with no flanges. It has a number of mounting holes fit for short drywall screws, but you can drill your own, anywhere but a knockout! Can't do that on a plastic box, they're too flimsy.

One or two of the holes is tapped specifically for a #10-32 ground screw. (-32 fine thread mandatory for electrical contact). They sell green screws that are ideal, but remember those panel ground bars I mentioned? They do not look out-of-place in a metal box. Aluminum grounds - solved!

Harper - Reinstate Monica
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    Tin not zinc, usually, but yes -- bog-standard N/G bars are plated Al, even on panels that otherwise use Cu buswork (like a QO) – ThreePhaseEel Feb 02 '22 at 01:12
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    Note that only the "swiss cheese" style of bar mounts with a 10-32 -- more typical 4-14 bars tend to mount using a #12 screw instead (same size as the setscrews) – ThreePhaseEel Feb 02 '22 at 01:13
  • The MacBlock connectors look like a quality product and more versatile than AlumiConns in the the former allow multiple wires in each port and accept larger size wires (up to #6). Do the MacBlock purple come with the antioxidant grease loaded, like AlumiConns do, or does the installer supply that? The AlumiConns are half the price of the Macblocks. – Jim Stewart Feb 02 '22 at 12:23
  • The MacBlocks come in two geometries, "straight" and "180 deg bend" which are functionally identical. Where would you want to use one vs the other? The straight one is referred to as "splice" and the other as "tap". The "tap" designation confused me. I expected the "tap" to have three ports so an original continuous wire would go straight through (or appear to do so) and another wire would be connected through a side port. Ref MAC-618-S-P MAC-618-T-P. – Jim Stewart Feb 02 '22 at 12:38
  • If the OP already has the connections in place in the boxes with the nails in the box but not driven, couldn't he just pull the nails out and substitute suitable long screws say with a self drilling tip? – Jim Stewart Feb 02 '22 at 13:05
  • Thank you everyone for your knowledge! The box with the rusted nails that was noted is not new. A licensed electrician put that in a few years ago when adding an attic fan and light. He spliced in a plastic box, with 14/2 cu and used the purple wire nuts. I simply followed his work for my lights. My work is the 2nd box without the rust on the nails leading to the LEDs. Considering everything is very accessible Im going to take these recommendations and switch those boxes to metal, grab some cable clamps, and replace the wire nuts with lugs. – TL DIY Feb 02 '22 at 15:38
  • To reiterate Jim Stewart's question above, does the MacBlock require antioxidant grease? If so, does Penetrox suffice? – TL DIY Feb 02 '22 at 15:39
  • @JimStewart Well the inline one is for when you are legally cutting an inline wire to tap it. (meaning you have >6" of length meaning the box is at least 12" across). I think most Al-Cu applications would find the other one to be more compact. I don't know if the Mac Blocks include no-alox, if not included it's not strictly legally required, but doesn't hurt. – Harper - Reinstate Monica Feb 02 '22 at 18:58
  • The problem is that plastic boxes aren't tough enough to mount any other way than designed. Running screws through those nail passages will just crack them. – Harper - Reinstate Monica Feb 02 '22 at 19:00
  • @TLDIY If it requires antioxidant, it will include it. There's never any harm in using it, especially since that area does have corrosion. – Harper - Reinstate Monica Feb 02 '22 at 19:01
  • There are long, small diameter screws that might fit in those nail passages, but of course any substitution could cause unforeseen problems and mght be a code violation. "No-Al-Ox" is a brand of antioxidant that goes back a long way and Jesse Aronstein does not recommend it. He recommended "Burndy Penetrox A". When I did my original pigtailing in 1980 of our aluminum wiring, I was unaware of Aronstein's recommendations and used No-Al-Ox, but later changed to Penetrox. My No-Al-Ox splices seem to have held up. – Jim Stewart Feb 02 '22 at 20:04
  • You could drill holes only a little smaller than the nails so you could gently drive the nails. – Jim Stewart Feb 02 '22 at 20:13