Connecting 6 gauge aluminum wiring to 10 gauge copper with AlumiConn

Question

I am replacing a 20 year old wall oven. When I opened the electrical box I noticed very large gauge aluminum wiring (6 gauge?). I purchased a box of AlumiConns (3 port style) to connect the aluminum wiring to the 10 gauge copper wire in my new oven.

Can I simply untwist a couple aluminum strands from the larger bundle? I plan to insert two aluminum strands into two ports on my AlumiConn and the 3rd port will go to the oven's copper wire.

Note in the 2nd photo below that there was no anti-corrosive paste inside the wire nuts. I was a little surprised how well this 20 year old connection stood the test of time, the wire nuts showed no sign of getting hot and the old copper and aluminum wire looked fresh. I'd still like to update the connection to current code and not have to worry about a future electrical fire decades from now.

While this isn't a dismissal of the risks, I've seen the same thing in joining aluminum and copper without paste and no evidence of corrosion (knock on wood). The real danger of such connections is that if they get warm the wires work loose and can cause an arcing situation. — Machavity, Jan 30 '19 at 03:51
Your right about arcing. I specifically looked to see if this 20 y/o connection showed signs of arcing but after unwrapping the electrical tape and untwisting all 3 nuts, I was surprised how fresh everything looked. I wonder if this was to code back in 1999/2000 (other than the missing nut to hold the armored cable from pulling out). — Julius Seizure, Jan 31 '19 at 19:10

ThreePhaseEel · Accepted Answer · 2019-05-02T03:33:33.713

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Use a mechanical lug connector ("Polaris" or equivalent)

AlumiConns are only rated for a maximum of 10AWG wire. For fatter work, you'll want their bigger brothers, mechanical lug connectors (sometimes called "Polaris connectors" after a common brand name) -- the smallest size of them is generally rated for wires anywhere from 14AWG to 4AWG, and as a rule, they are dual-rated for aluminum and copper wire.

You will also likely need a box extension ring or two, as mechanical lug connectors are quite chunky compared to wirenuts or Alumiconns, and you definitely need an appropriate connector to attach the flexible conduit to the box, as right now, it's violating several Code sections by flapping around in the breeze like that. If the extension rings aren't enough, then you'll have to replace the box with a small (6" by 6" by 4" should be ample) NEMA 1 (indoor) pull box, likely with a flush cover. These are what is used instead of a junction box when splicing large wires, and are available through electrical supply houses.

edited May 02 '19 at 03:33

answered Jan 30 '19 at 00:25

ThreePhaseEel

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Your right that stuffing 3 Polaris connectors won't fit. What type of box would work, assuming no restrictions. The empty space both behind and to the side of the new oven is absolutely huge. – Julius Seizure Jan 31 '19 at 19:15
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@JuliusSeizure -- if you need to replace the box, use a 6x6x4 NEMA 1 pull box -- they're what's typically used when splicing larger wires. – ThreePhaseEel Jan 31 '19 at 23:53
Since this post, you started recommending ILSCO's "Mac Block Connector". That's rated for up to #6, isn't it? – Harper - Reinstate Monica Feb 09 '22 at 20:55
@Harper-ReinstateMonica -- yeah, it sure is :) – ThreePhaseEel Feb 09 '22 at 23:51

Harper - Reinstate Monica · Answer 2 · 2019-11-26T03:54:42.237

Splitting #6 strands to fit on two #10 lugs

No, it's illegal to split wires like that. Aside from failing on 110.12 "neat and workmanlike", it is also paralleling (not allowed without special apparatus) and 110.3b "using a product inconsistent with it labeling/instructions".

You need a lug connector rated for #6. Looks like an Alumiconn but is rated for #6. This is readily available at any proper electrical supply, Home Depot won't have it of course.

Many mistakes in this box.

Whoa! You can't hang both the appliance neutral and ground onto the neutral wire!

You have a 4-wire connection back to the panel, noting the big Al ground wire. You cannot combine neutral and ground anywhere (except for the N-G equipotential bond in the main panel). So that neutral-neutral-ground 3-way splice is for the birds, and must go.

My advice would be to buy a $4 accessory ground bar that takes #6 wire (and is itself aluminum, therefore compatible with both Cu and Al wire). Saw off all but 3 voids and a mounting lug, mount the mounting lug to the #10-32 screw hole there in the junction box, and land the two ground wires on two voids. Solved!

Box is too small

Follow ThreePhaseEel's advice on the 6x6x4 box (144 c.i.) which will actually be comfortable! If you can't remove the old box, stack a 4x4 extension box on top of it - looks like this box but with an open back. I do not use knockout holes on extension boxes.

The FMC conduit needs a proper fitting.

The wires shouldn't be marked with tape those colors, unless your hookup is 3-phase "delta" power. Also you are not allowed to re-mark hots to be neutral. Neutral must be the wire natively colored white. The remaining wires can be red, black or blue; those are all legit hot colors.

That box needs to be bolted down to something

Not flopping around.

Don't use wire nuts here, and never tape wire nuts.

Wire nuts are not reliable with aluminum wire. These should be appropriate lug connectors (i.e. Alumiconns, but sized for #6 wire).

Never tape a wire nut. Refuse to tape them, then give the nuts a "pull test" - holding the nut and pulling each wire in turn. Failing the pull test means a poor connection that will arc-fault. Taping it hides this important warning sign.

Do tape nuts that are holding a single wire; they're not designed for that and don't work well there.

Ironically (per ThreePhase's answer) [Home Depot does sell lug connectors](https://www.homedepot.com/p/Polaris-4-14-AWG-Bagged-Insulated-Tap-Connector-Black-IT-4AB/303579042?MERCH=REC-_-PIPHorizontal1_rr-_-303578935-_-303579042-_-N), just not in-store — Machavity, Jan 30 '19 at 04:00

score 3 · Answer 3 · answered Nov 06 '19 at 03:58

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This was my solution to a very similar issue. I used a Square D 30 Amp Safety Disconnect Switch. The cost factor was about the same as purple twist on things that may or may not catch fire or Polaris connectors that have to be crammed into a 4" box. Its a little bigger than one, but, believing everything is right and safe makes it very appealing.

answered Nov 06 '19 at 03:58

Robert King

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Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably [take our tour](//diy.stackexchange.com/tour) so you'll know how best to contribute here. – Daniel Griscom Nov 06 '19 at 04:14
That's definitely a different way to solve the problem -- I take it this was on a 30A circuit, no? – ThreePhaseEel Nov 06 '19 at 04:32

score 2 · Answer 4 · edited Jun 16 '20 at 10:07

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Alumicons are rated for

Aluminum Wire Range: Min #12 / Max #10

Copper Wire Range: Min #18 / Max #10

So your #6 Al wire is way over, not even close. One way to go would be Al-Cu split bolts, but making these up properly takes some skill. You may need a box extension for that box, too.

The flexible metallic conduit is not connected to the box properly. You need a connector fitting.

edited Jun 16 '20 at 10:07

Community

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answered Jan 29 '19 at 23:42

batsplatsterson

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score 2 · Answer 5 · answered Nov 06 '19 at 16:55

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Use set-screw connectors like Polaris that are UL listed for the size. Also it would be a good idea to research the conductor and color selection, at very least figure out why the equipment ground is being accomplished by a blue neutral wire, the bare ground from the SE cable isn't terminated, and the metal box doesn't appear grounded.

answered Nov 06 '19 at 16:55

NoSparksPlease

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It looks like the hots and neutral in that SE cable were phase-taped, but whoever did the phase-taping had no white tape, oops! – ThreePhaseEel Nov 07 '19 at 01:08