Can I use exposed UF instead of THHN in conduit to outdoor AC disconnect?

Question

I'm installing a mini-split and need to run power outside to the disconnect box, then an additional line from the disconnect to the compressor unit. In most installs I've seen, power to the the disconnect (in circumstances where the line is not coming through the wall directly into the back of the disconnect--which is not an available option to me) comes through a conduit; in this case, I expect I'd use THHN in the conduit. Then, a whip is used from the disconnect to the compressor.

So, my questions:

1. Since UF cable is OK for use outdoors in exposed conditions, can I run UF (not in conduit) to the disconnect? (FWIW, I'll be using 12/2 UF on a dedicated 20A 240V circuit, although I don't think that detail is necessary for the question.)

2. A secondary question to #1: The lineset for the minisplit will be run in a decorative PVC cover secured to the outside wall. With the lineset inside the decorative cover will be the 14/3 communication wire between the compressor and the indoor air handler. Can I run the UF to the disconnect inside the decorative cover?

3. Instead of a whip (which is essentially a waterproof flexible conduit with THHN or such inside) can I use UF from the disconnect to the compressor unit?

Thanks,

AEP

Answer 1

UF cables can be installed outdoors without being in conduit unless it is somewhere where it could possibly be damaged. So no, it can't just be run plain to a disconnect and tacked to the wall. Any decorative PVC would have to be strong enough to provide protection for the cable. The same goes for the run from the disconnect to the compressor unit as it could definitely be damaged. Since it's hard to run UF in conduit, you'd be better off just installing the conduit and pulling individual conductors.

Answer 2

To answer your questions directly:

1. Typically for the USA, no. It must be protected within a code compliant raceway.

2. Typically for the USA, no. For the same reason given above.

3. Typically for the USA, yes. However, practically speaking and as further expanded on below, doing so is subject to additional rules depending on the specific regulations governing your jurisdiction. Generally, you would run a code compliant branch to a junction box within reach of the whip. It could take an unreasonable amount of effort to make the jump from the structure to the equipment connection point in a code compliant way - if your minisplit is a listed product, which for your sake you will want to make sure it is, then that whip is a tested component of the system. That is, the code will deem it "safe" to make that jump unsupported; the code will not relax the requirements for sufficient support and protection over the same span.

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To go beyond what you are asking to offer some general code context:

You'll need to figure out the regulations that govern your jurisdiction and the impact it has on the specific configuration of the work you are intending.

For example, the general typical building code in the USA permits the installation of an underground feeder to a sub panel to utilize UF cable run without shielding from damage buried an appropriate depth given anticipated loads above (typically 24" min) in proper substrate (typically bedded and backfilled in smooth granular material) transitioning to an allowable shielding where it turns up above ground (and that raceway is subject to additional rules, such as needing to be sealed in accordance with the electrical regulations if so required in effect to prevent moisture from contacting energized live parts).

From that point - whatever the nature of the load center you are pulling from, be it the primary service panel or a sub-panel - you would typically run NMB through the structure "indoors", transitioning to code compliant protective raceway to make the jump between structure and equipment "outdoors". If NMB is not allowable or not feasible for some other reason, you can either run UF cable the whole run, following same rules as you would for running NMB indoors; or, if you are stuck using THHN, then you would have to bear the cost of conduit the whole way both inside and out.

Here's a simple blog post, but ECM will go into more depth into the specific regulations.

Good luck and have fun!

Answer 3

When used above ground it has to be used as required in the NM Section 334, where it says:

334.15 Exposed Work In exposed work, except as provided in 300.11(A), cable shall be installed as specified in 334.15(A) through (C).
(A) To Follow Surface. Cable shall closely follow the surface of the building finish or of running boards.
(B) Protection from Physical Damage. Cable shall be protected from physical damage where necessary by rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC rigid nonmetallic conduit, or other approved means...

"where necessary" and "other approved means" gives the AHJ a lot of room to make your proposal difficult.