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My new AC system will include two motor loads:

  • Central AC (Rheem RA1642): 208/230-1-60, 40A MOCP, 25A MCA, 20.2A rated load
  • Minisplit (Fujitsu 12RLFW1): 208/230-1-60, 20A MOCP, 12A MCA, 5.9A rated load

I also intend to provide a 120 VAC 15A GFCI outlet.

I propose to install the GFCI outlet on one pole of the circuit feeding the 20A disconnect. NEC table 201.24 permits a 15A receptacle on a 20A branch circuit (see this question). Based on NEC 210.23(A)(1)&(2) the max permissible receptacle load would be 16A and the max permissible utilization load would be 10A. With a 15A outlet and an AC rated at 5.9A heating (4.4A cooling) I should be within these limits.

Has anyone experienced GFCI nuisance trips hanging such an outlet on one pole of a circuit with a two-pole motor load like this? I wonder whether a transient voltage from the motor turning on/off might cause a trip?

The 40A disconnect will remain on a dedicated 40A circuit.

The wiring would go as follows:

  • Central AC: 60A fusible NEMA 3R disconnect (with 40A RK5 fuses), #8 THWN to internal jbox, 8/2 NM-B to service panel with 40A 2-pole breaker.

    Minisplit + GFCI: 30A fusible NEMA 3R disconnect (with 20A RK5 fuses), #12 THWN to internal jbox, 12/3 NM-B to service panel with 20A 2-pole breaker. GFCI outlet either integrated in disconnect panel or in separate weatherproof box.

I will run #10 Cu ground wire. All THWN to run above ground in shared conduit thru and along outside of brick wall under an eave in Virginia. For ampacity, no temperature correction has been applied but 5 current-carrying wires in conduit calls for an 80% adjustment. For conduit fill we have 2@#8 (0.213), 1@#10 (0.161), 3@#12 (0.128). With 3/4 SCH 40 PVC conduit I estimate less than 30% fill (I am permitted 40%).

Any comments or concerns about this plan?

Thanks for the initial feedback. I've edited to clarify the requirements. Here's a link to my original (and more muddled?) question.

From sub-panel to outside From sub-panel to outside

Along the outside wall Along the outside wall

A rough wiring schematic Two disconnects shown as dashed boxes with GFCI outlet and lugs for fused circuits and ground.

Wiring schematic

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I don't like putting the maintenance receptacle on the same circuit as the equipment, especially when you have capacity to do otherwise.

You only need one ground, sized for 40A, so 2@#8, 1@#10, 4@#12 is less than 30% of PVC sch40 fill.

You might be better off eliminating all #12's except the white, upsizing your feeder one size to 60A #6 CU feed to a single outdoor 6 space NEMA 3R panel and using 3 separate breakers rather than mounting a j-box to split the feed or routing feeds through disconnects. Conduit fill will only be 27%.

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  • What's the specific concern about circuit sharing? Is a GFCI outlet on one pole of a 2-pole motor circuit a concern for nuisance trips? I'm having trouble locating an inexpensive 6 space NEMA 3R panel. Have a PN in mind? – Stanwood Jul 26 at 2:35
  • Fastened in place equipment is limited to 50% of a circuit when shared with receptacles, your previous question said the circuit ampacity of the split was 13A. I would call local wholesale houses looking for a HOM612L100RBCP homedepot.com/p/… – NoSparksPlease Jul 26 at 3:59
  • Shared circuit restriction is NEC 210.23(A)(2) and fujitsugeneral.com/us/resources/pdf/support/downloads/… says MCA 12A. – NoSparksPlease Jul 26 at 4:25
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    Thanks big time for the panel link, NEC reference, and minisplit spec sheet. I've had a heck of a time navigating the Fujitsu website. This link provides MCA, rated current, and max operating current for my exact model. Which I didn't have before. I will update my question accordingly. Please have a look and comment. – Stanwood Jul 26 at 11:43
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Yes. What NoSparksPlease +1 said. Install a subpanel INSTEAD of disconnects.

There's no requirement whatsoever for a disconnect switch. What is required is any one of

  • A. line-of-sight to the circuit breaker that feeds it, or
  • B. a disconnect switch in that line-of-sight, or
  • C. a lock frame for Lockout/Tagout on the non-line-of-sight supply breaker

Since you do not want to do C, you are better off doing A with an appropriately-located subpanel, because that will actually be cheaper all-in-all. The breaker cost will be a wash since they'll be in the subpanel instead of the main. The only added cost is the feed 70A breaker ($17), and the subpanel proper ($15 for a 6-space, but remember what we always say about going big!) Versus the cost of the disconnects and that menagerie of wire. Here you only need 3x #6 or 3x #4 Al) and 1x #8 ground, and get to breaker it at 70A. (65A wire limit @ 75C, rounded up to the next available breaker size).

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  • Just FYI I went with 60A feed based on MCA in his previous question, 25 + 13.4 left plenty of room for a 20A service circuit, keeps the ground @#10, and covers if he has 60°C terminations. – NoSparksPlease Jul 24 at 18:25
  • @NoSparksPlease Oh you're correct. It's just an artifact of how the 75C column in 310.15(B)(16) interacts with 'round up'. You get #8 at 50A or #6 at 70A. – Harper - Reinstate Monica Jul 25 at 3:19
  • HVAC pro has stressed he wants fused disconnects (not breakers). I figure he services the equipment and recommends these for a reason. Have a PN for a $15 6-space panel? – Stanwood Jul 26 at 2:38
  • I worked 10 years as an electrician for HVAC contractor, usually they spec'd fusible disconnects because some equipment specifies fuses, and it allows them to substitute or swap out equipment if you supply fusible disconnects. Also many states HVAC techs can't legally replace defective breakers or change size if needed. You already disclosed the products you already selected can use breakers, and it's likely you can swap a breaker yourself if needed. – NoSparksPlease Jul 26 at 4:21

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