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I am wiring two new circuits for a geothermal furnace.

For the 6/2 AWG circuit, a standard 60A disconnect switch is fine. There are two line lugs , two load lugs, and two ground lugs.

For the 6/3 AWG circuit, it seems I am two lugs short. I see three pole disconnects that are quite a bit more expensive. Can anyone provide a reference disconnect switch I can utilize? I am unclear if a two pole disconnect could properly do the job.

Electrical details for unit:

Here's the electrical specs (highlighted in yellow for the particular model I am working with).

How I read those details:

  • A 60A circuit for the auxiliary heater. I opted for 6/3 romex. Perhaps I do not need the 3rd conductor?
  • A 50A circuit for the geothermal unit (under electrical data) with 6/2 romex.
Davek804
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    Why does the geothermal furnace need /3 cable? Most furnaces are single voltage (120V *or* 240V). Also you know #6 Romex is only 55A wire, right? The breaker can be 60A but the load (adjusted) must be <=55A. – Harper - Reinstate Monica Feb 16 '23 at 00:26
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    Thanks for reading. I edited the post to include the highlighted electrical specs for my particular unit. Additionally, the full install manual details electrical information on Page 15, here: https://www.waterfurnace.com/literature/7series/im2700anb.pdf. – Davek804 Feb 16 '23 at 00:46
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    I'm confused and we need more details about your installation. All equipment listed in the manual is 230V/60Hz/1P so I'm unclear on why the 6/3 cable is required unless you're serving one piece of equipment from the 6/2 and two additional separate pieces of equipment from the 6/3 configured as a MWBC. – Chris O Feb 16 '23 at 00:56
  • Only one geothermal furnace is being installed. The furnace also utilizes an integrated auxiliary heater. More specifically, a Waterfurnace 7 Series NVV048 (4-ton) is the furnace and the auxiliary heater is the EAL(H)10. In the installation manual, I see the following quote: "All 208/230 units are factory wired for 230 volt operation. For 208 volt operation, the red and blue transformer wires must be switched on terminal strip PS." I hope I am not adding to any confusion. I am happy to answer any specific questions. – Davek804 Feb 16 '23 at 01:02
  • @ChrisO upon further review of the aux heater, it looks like needs only L1, L2, and G. So I believe 6/2 should suffice. Would you agree? It seems like I still need two distinct circuits. – Davek804 Feb 16 '23 at 01:36
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    Did you already buy/install the 6/3 cable @Davek804? – ThreePhaseEel Feb 16 '23 at 02:10
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    Ha. Yeah. I did. And it's mounted. And I'm already pretty sure that I wasted a pile of money by cutting a portion of it. You live and you learn, man. But it's a pricey lesson. I've asked a more detailed circuitry question based on what I've learned from this thread. Link: https://diy.stackexchange.com/questions/267033/required-circuits-for-waterfurnace-geothermal-unit-and-aux-heater – Davek804 Feb 16 '23 at 02:44
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    What you did was simply pre-wired for a small subpanel to be placed there in the future. TBH, any time I'm installing a hydronic system that is going to have a boiler, 1 or 2 pumps, various control electronics, etc., I pull one big feeder and install a small 8 or 12 space subpanel for all the little branch circuits. Saves wire and effort in the long run. – Chris O Feb 16 '23 at 15:58

1 Answers1

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Since you've already purchased and installed the 6/3 even though 6/2 would have done the trick...

Just leave the white wire (since white = neutral in NEC land) disconnected and capped at both ends. Connect the black and red to your 2-pole disconnect and call it good.

FreeMan
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  • Or just connect the neutrals with a wire nut or equivalent? – keshlam Feb 16 '23 at 14:15
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    No reason _currently_ @keshlam, for the neutral to continue on to the equipment. However, it would make sense to do so for any potential future use. By capping both ends in the disconnect, it makes it extra _abundantly_ clear to any future maintainer that it's not in use. Of course, nothing would prevent one from simply splicing them in a safe area of the box for pass through, either. Up to the OP on that one. – FreeMan Feb 16 '23 at 15:49
  • Entirely valid, @freeman. – keshlam Feb 16 '23 at 22:40