Mini split wiring

[kwired]

If you are required to have a disconnect switch at the air handler, a basic 2 pole wall switch is all you need. You do not need a 3 pole switch. The control line is low voltage and may even be optically coupled further reducing any shock hazard.

My thoughts on this are you don't need a disconnect at the air handler anyway unless it is rated over 1/8 hp or 300VA. It has no hermetic compressor so 440 doesn't apply to it.

Never seen a minisplit with large enough motor/VA rating that would kick in that requirement. If there is one out there, they might want to rethink that "mini" in the name.:happyyes:

 

[MattS87]

The manufacturer of this unit is LG. I just re-read the install instructions (which suck if you ask me), and it mentions #12 for the feed with 20A fuses which i have. Then i found a section that mentioned control cable between the 2 units to be #18. I did find where it said stranded wire is to be used though. Overall, i believe how most of us wire them works perfectly fine I was more curious if any of you knew or had heard of this "must be #14 between indoor/outdoor units" which seems to be a resounding NO. Glad to see I wasn't overlooking something here

 

[sparky1118]

I install and wire mini splits and I know some brands do indeed require stranded over solid wire. I am sure that it would work fine however if there is ever an issue with the unit and they needed someone from the company to come out they may not warranty the product since it wasn’t done to their specifications


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[jumper]

I install and wire mini splits and I know some brands do indeed require stranded over solid wire. I am sure that it would work fine however if there is ever an issue with the unit and they needed someone from the company to come out they may not warranty the product since it wasn’t done to their specifications


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What type of control signal is being sent down these wires?

I can only think of a few things that maybe say stranded could be better.

 

[ritelec]

??? interesting. I've installed a few with solid wire between the two and never any issues.

thanks for bringing it to my attention, research shows sj chord and even this cable ( https://www.southwire.com/oem/ez-in.htm ) being used.

also read about an install, solid went in and no problem for a month, then got a E1 communication error. He changed it to 19 strand conductor and it didn't work then changed it to 40 strand and it worked...

This will have me thinking next time I have to wire one.. thank you..

or I can leave the interconnect to the AC guys as their always into doing it ;- )

 

[SkyNetInc]

The indoor unit is 208/240 volts NOT low voltage. You should be using a Chapter 3 wiring method between the units.

All the spec's I see for Mitsubishi and Fujitsu call for #14 between the units but I don't see why you couldn't use larger wire. Going smaller is definitely not acceptable.

False (at least on the Mitsubishi's I'm currently installing). Panel (15a, 14awg) to outdoor unit = 220v. Outdoor unit ---> Indoor unit = 18vdc via 16awg stranded(?...don't quote me on that...I don't have specs in front of me...running on memory). I'll post the specs after this weekend (manuals are at the house I'm wiring) if you still don't believe me. There is NO AC voltage at the interior "head" unit. Had to explain all this to the inspector, too, who wanted a disco at the inside units. No, no and no.

 

[GoldDigger]

You can use larger wire, I wired plenty of these. Most of them took a 2P/30A disco feed. I used 10/3 for signaling wire and they worked perfect.

If you are required to have a disconnect switch at the air handler, a basic 2 pole wall switch is all you need. You do not need a 3 pole switch. The control line is low voltage and may even be optically coupled further reducing any shock hazard.

At least one brand (Mitsubishi) uses a Line to Line 240 volt connection (no neutral) and the "control" wire is voltage referenced to one of the line conductors (i.e. 120V to ground) and there is no indication that it is power limited. I would definitely use a three pole switch for those units

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[Adamjamma]

What type of control signal is being sent down these wires?

I can only think of a few things that maybe say stranded could be better.

Sounds like they are using radio signals through the wires... different frequencies at same time, separated by filters at the one end... which is why they want stranded as solid mixes the signals more , causes more hash to the signal. Might also explain the call for 18 rather than any other sizes... because they are sending radio signals not voltage...

 

[SkyNetInc]

False (at least on the Mitsubishi's I'm currently installing). Panel (15a, 14awg) to outdoor unit = 220v. Outdoor unit ---> Indoor unit = 18vdc via 16awg stranded(?...don't quote me on that...I don't have specs in front of me...running on memory). I'll post the specs after this weekend (manuals are at the house I'm wiring) if you still don't believe me. There is NO AC voltage at the interior "head" unit. Had to explain all this to the inspector, too, who wanted a disco at the inside units. No, no and no.

Oops...my bad. Just checked out the manual online. Was referring to the control wire (12-24vdc), not the power wire (208/230vac). Power wire is in fact 14/4awg stranded THWN. :ashamed1:

 

[romex jockey]

These units may be effective, but the visual on the installation is just fugly.

Yup

The 'mini split' cabal hits/runs around here a lot, always a mess....

It's frustrating trying to tell a customer just how wrong something that can work perfectly fine may be

~RJ~

 

[hbiss]

Sounds like they are using radio signals through the wires... different frequencies at same time, separated by filters at the one end... which is why they want stranded as solid mixes the signals more , causes more hash to the signal. Might also explain the call for 18 rather than any other sizes... because they are sending radio signals not voltage...

Don't quit your day job.:happysad:

-Hal

 

[Andy Delle]

Sounds like they are using radio signals through the wires... different frequencies at same time, separated by filters at the one end... which is why they want stranded as solid mixes the signals more , causes more hash to the signal. Might also explain the call for 18 rather than any other sizes... because they are sending radio signals not voltage...

It's simple low bandwidth serial communications, again about 1200baud - slow. Doesn't need to be fast which would require a shielded cable or coax. I mean what is it communicating? Compressor off/on and speed control with a variable compressor. Perhaps some error information or outside temp comes back to be displayed on the remote control. Not much information exchange at all.

 

[Andy Delle]

At least one brand (Mitsubishi) uses a Line to Line 240 volt connection (no neutral) and the "control" wire is voltage referenced to one of the line conductors (i.e. 120V to ground) and there is no indication that it is power limited. I would definitely use a three pole switch for those units

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Well even if referenced to the line, just how much current can flow over the control wire? If it's a data signal, it;'s a few volts in the microamp range limited by the control circuitry. Which btw, could be a problem if switched with a 20a switch. Low level signals through high current switches are often lost due to contact resistance and oxidation. That's why many relay vendors specify a minimum current on some products and offer low current versions.

Now if the return is simply line voltage to a relay coil, there could be some danger there. But I think in most of these units it is a data signal. One way to tell is if there is a board inside with with lots of electronic components on it. Remember Minisplits are all about efficiency and many have variable speed compressors running off small VFD's. It's not your old basic 24v relay in the condenser like bigger split units have.