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I would like to connect 6 gauge aluminum wire to 12 gauge copper wire. Is an aluminum splicer/reducer suitable for this in the USA? An example is the Morris 90612. It is a rectangular aluminum block with holes on the ends to accept the wires that are then held down by screws. It of course requires antioxidant and insulation, probably rubber and vinyl electrical tape.

There is much discussion about Al to Cu connections here and elsewhere on the web, but the common solutions either don't handle 6 gauge or are in my opinion overpriced for the task. Split bolts are another option, but I wanted to avoid the awkward shape, especially when it comes to insulating.

I think the item I am a referring to has been mentioned here as something like a mechanical lug. It almost seems like a slam-dunk that it is suitable since it is AL9CU dual rated, but there are many things that might not be obvious in the rules. In the Q&A section at one of the big box store websites, a customer service rep said another brand nearly identical and also AL9CU was not rated for this. The only reason I could think of is if the wires are inserted too far and become intermixed. Some versions are said to isolate the two sides.

This is to make a pigtail to connect the 6 gauge aluminum to a 20 amp breaker with an 8 gauge maximum. The splice would be in the breaker panel, which has plenty of open space. The old 40 amp breaker is beyond the required maximum overcurrent protection for a new heat pump.

I could avoid the whole aluminum to copper thing if thinner aluminum wire were readily available for the pigtail. I don't want to go to the effort of trying to replace the wire all the way out to the heat pump.

Sorry so long-winded, but I think of what might be misunderstood and add detail. Thanks for reading and all the past answers I read.

EDIT: Morris tech support told me not to use 90612 for this. Details in comments below.

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    I'm fairly sure that Code requires an outside disconnect for any heat pump. Code doesn't care what kind you use. One option is to leave the 40A breaker in the panel, and use a "2 space subpanel" style of disconnect with a 20A breaker in it. That will also take care of the Cu/Al splicing for you :) May 20, 2023 at 5:53
  • There is already an outside disconnect. The original oversized and inefficient 3 ton condenser is replaced with a 1.5 ton, thus the reduction in breaker amperage. Considered replacing it with fusible type, but too costly. Subpanel is the same thing. Thanks for the additional idea.
    – HHH
    May 20, 2023 at 15:21
  • When I say too costly, it is from the standpoint of being off by just one gauge on the breaker. Your idea made quite a bit of sense if it were not a replacement heat pump.
    – HHH
    May 20, 2023 at 15:50
  • A subpanel and breaker will very likely cost less than suitable connectors, and suits the replacement heat pump perfectly.
    – Ecnerwal
    May 20, 2023 at 16:00
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    @HHH -- that is very strange that an Al/Cu rated multiport connector can't handle a copper wire in one hole and an aluminum wire in a different hole May 26, 2023 at 1:56

1 Answer 1

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You need a disconnect out at the outdoor unit.

NEC isn't particular about what kind you use. If you want to use a pullout disconnect, hunky dory. A big knife switch disconnect, fine. A "2 space subpanel" with a 20A breaker in it, also acceptable.

Did you catch that last one where the disconnect has a 20A breaker in it? :)

Yeah. That's alright.

Leave the 40A breaker in the panel. Bring your 40A #6 aluminum wire out to the (new, I presume) "2 space subpanel" style disconnect. Fit a 20A breaker there.

  • Disconnect, check.
  • <=50A breaker protecting #6 feeder, check.
  • <=20A breaker protecting heat pump, check.
  • Passes inspection without worry, check.
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  • Simple and elegant, though I'd guess there probably IS already a disconnect there. But replacing it with a sub-panel if it's unfused solves this neatly. In the unlikely event that the old wiring has a neutral, you could even use a 4-space and cover the service outlet.
    – Ecnerwal
    May 20, 2023 at 12:55
  • Yes, already have disconnect. See comments under the original question. Amazing that a whole subpanel is less than 2 connectors.
    – HHH
    May 20, 2023 at 16:23

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