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The air handler for my heat pump has supplemental electrical heating. Currently it seems to be fed by aluminum wire, I think a service line bundle of 1/0 gauge. The breaker is 240V, 125 amps.

If I'm reading the electrical information label on the unit, however, it seems I'd need to size the wire for 85 amps and the breaker should be no more than 90 amps. There's only two hot wires running to the unit, so I assume it is in the "Single" section with just L1/L2. So the aluminum wire is correctly sized, but not the breaker. I'm thinking the 125 amp breaker was just what someone had in their truck on the install day...

Am I reading this label correctly? Are there any other considerations, such as any power the unit needs for the blower or is that already included in the label? There are no other electrical lines from my load center running to the air handler, and no boxes, breakers, fuses, or anything in between.

Electrical info label on air handler

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    Wire size can usually be larger than needed. Do seem to have a problem with the breaker size. Manufacturers instructions/label have to be obey, so the 125 amp breaker is against code/should not pass inspection.
    – crip659
    Commented Jan 12 at 18:05
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    The breaker would be okay if you have 90 amp fuse/breaker protection at the heat pump disconnect.
    – crip659
    Commented Jan 12 at 18:34
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    You said 230V, if that's correct this label is pretty clear.
    – KMJ
    Commented Jan 12 at 18:46
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    It probably changes nothing since wire insulation is rated likely rated for 75°C, but wire size is 125% of minimum circuit ampacity, so 104.25A. #1 AL is only rated for 100A, so really 1/0 is the minimum size. If you have 90A fuses or breaker at the maintenance disconnect then 125A in panel is OK since 1/0 is rated for 120A, 120A is not a standard breaker size, so you can upsize to 125A breaker. If your maintenance disconnect is unfused or larger than 90A then you will need to change the panel breaker to 90A. So the question is what type of wire is feeding this?
    – NoSparksPlease
    Commented Jan 12 at 20:41
  • Can you post a photo of the indoor unit's wiring diagram mean please?
    – ThreePhaseEel
    Commented Jan 13 at 4:11

1 Answer 1

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The breaker is oversized, unless you have a second breaker at the unit. The maximum overcurrent protection required depends on whether you have single or dual heaters. Your assumption that it is single because you have only two hot wires to the unit seems premature, as dual heaters would still have only two hots (L1/L2). The distinction is important, as the breakers need to be sized accordingly. You should be able to find the spec on which one you have, and then replace the 125A breaker with 90A (dual) or 60A (single).

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  • if it were dual, what would the wiring look like? ideally, wouldnt there be two 240v breakers: one with two hots feeding L1/L2 and the other with two hots feeding L3/L4? therefore 4 total hots going to the unit? in case im making a mistake in terminology, by "hots" i mean opposing sides of the split phase (eg, a black and a red wire with a 240v difference between them).
    – tau
    Commented Jan 12 at 21:53
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    What do the terminations in the unit look like? Are there 4 terminations points, or just 2? "UL" often surprises me, but I would expect a single (90A) termination to be to an internal fuse block that breaks out elements to be protected at 48A or smaller loads protected at 60A or less (to comply with NEC 424.22(B)). If you're trying to determine if your electrician installed a single feed to something that requires dual feeds then edit your post with picture of wiring diagram from panel door and picture of terminations.
    – NoSparksPlease
    Commented Jan 13 at 0:35
  • i think your expectations are correct. i am not at the house, but i dont see a wiring diagram for the heat package in my photos. i do see the L1, L2, L3, L4 aluminum lugs, 2 ground lugs, and 4 fuses though. the L1 and L2 fuses are much larger than the L3 and L4 fuses (probably why the label says 58.5a and 25a, respectively). also, i wasnt the one to disassemble the unit (its current state), but i didnt see any sort of single-point adapter kit. 125a breaker in any context doesnt seem to make sense; theres no permit for this and im really starting to think it was a "whatevers in my truck" job.
    – tau
    Commented Jan 13 at 0:54
  • oops, just realized my comment is kind of misleading and i am unable to edit it now. i shouldve said something more like "i think your expectations are how it should work too, but i suspect mine does not work that way and is probably installed incorrectly". if i found a single-point adapter for the fuse block, then i think your expectation wouldve been spot on.
    – tau
    Commented Jan 13 at 1:42
  • The wiring diagram I would be looking for is usually on the inside of the door or on the backside of the removable cover.
    – NoSparksPlease
    Commented Jan 13 at 17:44

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