Simple question and I am obviously missing something, but the manual calls for 14/4 to be used as the communication/power cable. That is 1 wire for communication, 2 hot wires and lastly one for ground. Could I simply use 14/3 w/g - that is your typical romex? The only difference seems to be with the romex the ground is a bare wire.

Thanks in advance!

  • 14/4 is not the same as 14/3. If they wanted you to use 14/3 they would say so. May 11 '20 at 5:57
  • @Harper-ReinstateMonica -- the mini split makers are not accounting for the quirky way North American mains cables are spec'ed May 11 '20 at 11:48

This is because most mini splits are meant for a global audience

One of the quirky things about mini-split air conditioners is that they are basically the air conditioner of choice if you want central air conditioning outside of North American and the existing installed base in places like Europe and Australia. North American-style split systems simply aren't used in the rest of the world, for a variety of reasons that have largely to do with space and efficiency, and as thus, mini-split manuals are written for a global audience, not a US one, even when written in English by major global manufacturers who are used to selling to North America (such as Mitsubishi).

One artefact of this is that they often specify cables in a way that's only crudely translated to US nomenclature. Most of the time in the rest of the world, something akin to a tray cable is used, and in tray cable nomenclature, the green wire is counted among the wires of the cable, as it may or may not be necessary as an equipment grounding conductor, depending on the application of the tray cable. However, Exposed Rating/Joist Pull rated tray cables (designated TC-ER-JP), the only ones that can legally be used without conduit in a dwelling unit application under the NEC (as per NEC 336.10 point 9), are thin on the ground from what I can tell; many HVAC sellers will try to sell you tray cable as "mini-split cable", but it's not appropriate for the application.

So, I'd run individual 14AWG THHNs (black, black, red) up the flex whip to the disconnect box, then tie them into 14/3 W/G NM at the AC disconnect with black and a remarked white for the hot wires in the NM cable, red for the comms wire, and the ground of course tied to the disconnect's ground terminal. Then, this 14/3 W/G NM can be run to the indoor unit, just like you would run any other mains circuit. (Of course, if you're under codes that prohibit NM, you can substitute a MC or AC cable instead, or individual 14AWG THHN wires in metal conduit for that matter.)

  • Thanks for the thorough explanation! And the idea of tying up the romex and THHN in the disconnect.
    – ecco88
    May 11 '20 at 12:18
  • Also, the manual appears to call for a fused disconnect - the place I bought it from did spec out a nonfused disconnect. I thought might double check because not sure why the fused disconnect when it is on a dedicated circuit. That coupled with finding a 45Amp disconnect is very difficult.
    – ecco88
    May 11 '20 at 12:24
  • @ecco88 -- do you have the unit in front of you (so you can look at its nameplate), or has it yet to arrive/be ordered? (And if you did need a fused disconnect, those only come in two sizes, 30A and 60A, corresponding to the two smallest case sizes available for ordinary (Class RK5) mains fuses May 11 '20 at 12:33
  • Yes delivered - lg lmu420hhv
    – ecco88
    May 11 '20 at 12:34
  • @ecco88 -- does the outdoor unit's nameplate say "maximum fuse size", or does it say "maximum OCPD size" or something like that that doesn't explicitly state "fuse" by itself? May 11 '20 at 12:36

I just finished wiring a Fujitsu mini-split system for my son's new house build (3 indoor units and one outdoor unit). The wiring was very simple: 14/3 with ground between the indoor units and outdoor unit. 10/2 with ground to the outdoor unit from the panel.

As others have said: these are international units and the English versions of the manual use odd terms. For instance a GFCI is an "Earth Leakage Breaker", a ground wire is an "Earthing wire".

Regarding the fused disconnect, yes, the installer wanted a disconnect with actual fuses, not a circuit breaker and certainly not a simple switch.

Last year I also wired up a Mitsubishi mini-split for a home my mother owns. If I remember right there was a very convenient color coded cable (4 conductor, I think), that made it super simple to connect. I believe it was all low voltage. If the OP wants, I could research again, but the install manuals should clearly show what the cabling requirements are.

What brand mini-split is being installed?

  • LG - LMU420HHV is the model of the condenser.
    – ecco88
    May 11 '20 at 17:07
  • I just spent a few minutes in the installation manual for your unit and the English is terrible. One of the worst I've seen, IE: quote from manual: "Also when handling storage, pipe must be careful to prevent a fracture, deformity and wound" The specs for the wiring are unclear. The OP will probably have to contact an experienced installer to sort this out. May 11 '20 at 17:27
  • SMH, how do these manuals get past the UL Listing process or other competent NRTL? Is this some GATT thing we have to do, accept their foreign certification as they accept ours? At least ours are any good. May 11 '20 at 20:59
  • Fully agree Harp. While I've run across a few odd terms here and there like "earth leakage breaker", at least it's just a different name for something and we just have to sort out the terminology. But the LG manual for the condenser had terrible English throughout it. If you want a good laugh and be disgusted at the same time, see if you can run down a copy of it. It's bad. And the "warnings" and "cautions" are like "don't let it fall on you", etc. May 11 '20 at 22:13
  • OK, I know we aren't supposed to chit chat here, but begging some tolerance from the moderators during this frustrating lockdown time. Here is one of the "best" cautions I read in the manual: "Do not use an appliance for special purposes such as preserving animals vegetables, precision machine, or art articles. - Otherwise, it may damage your properties." Let's just say it never would have occurred to me to use a mini-split system condenser to preserve animals vegetables,..etc. LOL May 11 '20 at 22:37

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