Circuitry & Wiring Specifications for Installing Ductless Mini-Splits & HVAC Units

LG Ductless Mini-Split
LG LS120HEV2 12000 BTU Mega Series Single Zone System with Heat Pump

Ductless mini splits are one of the most popular AC choices for homeowners and businesses alike. We sell tons of mini split air conditioners each day on our website, and, on our blog, have previously written about all the benefits of and features to consider when purchasing a mini-split AC of your own.

Installing ductless mini splits requires a high level of electrical knowledge in order for the job to be done safely and without harm to yourself or the unit. For that reason, we do not recommend homeowners try to install the unit themselves. Unless you are an advanced DIYer with extensive experience in electrical work, we strongly advise you hire a professional to get the job done.

But even professionals have to learn the ropes, and so if you are an electrician who simply has not undertaken a mini split installation project before, this post is for you. Here, we offer a step-by-step guide to everything you need to know about the electrical specifications for installing ductless mini splits.

NOTE: These instructions are in regards to electrical specifications only, and do not include line set installation or refrigerant set-up.

 

How to Wire a Mini Split System

Follow these steps to wire up your ductless mini split system

Step 1 – Mini-Split Shut-off box:

Run a 230/208 volt or 115 volt* dedicated line from the main break box to the area where the shut-off box will be installed next to the unit.

* Voltage depends on the system. The vast majority of mini-split units are 230/208V, but there are some that are 115V.
 

Step 2 – Mini-Split Wiring:

Mount the shut off box on the outside wall and connect the wires from the break box.

Electrical Shut off box

electrical shutoff box detail
208/230 Volt Shut Off Box

In order to meet code, you must have a shutoff box at the location of the unit. This makes system repairs safer and easier. Wire the two hot leads to the fused connections in the box and the ground to the provided connection. Then, reattach the faceplate and insert the on/off switch. It should be kept in the off position while you continue to work on the unit.
 

Step 3 – Electrical Wire Whip:

Attach an electrical whip to the shut-off box and run it to the unit.

Electrical Whip
An electrical whip is a premade, outdoor grade wire set that is intended to run from a shutoff box to the unit being installed. Using this ensures that you will have no issues with meeting code and keeps the process simple for you. The whip must be wired into the shutoff box and then to the unit as we will talk about next.
Alternatively, run your own wire through an outdoor grade conduit so that is protected from the elements. (an electrical whip is simply a pre-done version of this.)

 

Step 4 – Mini-Split Wire Connection to Base:

Connect the wires to the unit based on the instruction manual.

IMG_7004
While it might be difficult to see through the other wiring in the unit, here we have included a picture of the main power connections to a Friedrich Mini Split Unit. You can see the green, black, and red wires connect the terminal blocks on the bottom right. The exact details of a connection like this are specific to your unit. Always reference the instruction manual before attempting any electrical connections.

LG Wiring Diagram
 

Step 5 – Mini-Split Wiring Connecting Inside to Outside Unit:

Connect the wire for the indoor unit to the outdoor unit.

Mini Split Wiring
Depending on whether you are installing a single zone or a multi-zone unit, you will have a different number of connections. This Friedrich multi-zone unit has connections for 4 units, all of which are numbered for easy cross-referencing to the indoor unit. Make sure to write down which wire color is connected to which number. It is also critical to make sure that each indoor unit on a multi-zone system is wired to the same input that its line set is connected to. Otherwise, the system will not operate correctly.
It is recommended to use 14 gauge stranded wire for installation. Pictured is 14 gauge solid wire which will work, but should only be used if stranded wire is unavailable. Total Home Supply offer Honeywell 14/4 Mini Split wire in 50 ft and 250 ft rolls.
 

Step 6 – Mini-Split Installation Complete:

Run the wire inside.

Indoor Mini Split Electrical
Just like the outdoor unit, the indoor connections must be made in the correct order. Connect the 3 main wires along with the ground to their respective terminals. Some manufacturers recommend using round crimp style terminals for a more secure connection.

After this, the electrical portion of the installation is done! Congratulations!
2015-07-28_2006

If you have any further questions regarding the electrical specifications of installing ductless mini splits, please do not hesitate to contact us at 1-877-847-0050 and speak to one of our qualified representatives.

Ready for the next step? Check out our multi zone mini split buying guide!

Kristen Turner

Featured blogger for Total Home Supply.

52 comments

  • Great information but I have a question. I’m installing 2 multi split system in my house. The condenser requires a 30 amp breaker. It also calls for 12-3 cables from the outdoor condenser to each unit. But my question is, what wire do I need to run from the main panel to the outdoor box since I’m installing 2 multi split systems?

  • Our electrician says he will install 220v for our 230v/208v mini split. He says 220 and 230 are the same. Is this accurate?

  • If my split system is 220 v how do I connect it to my 110 V supply?

    is there a transformer in the unit?
    Do I need to buy a transformer?

  • Please help anyone who might know. I need a dual zone mini split unit the is only 115 volts. This is for a disaster relief trailer we are building for Tyson foods. We are limited to 115 volt power supply. Any suggestions are welcome.

    • Unfortunately, none of the major manufacturers make a multi-zone unit that is 115 volts. You could use two single zones instead.

  • I am planning on using dedicated 6-3 UF wire w/ 50amp breaker to exterior 30amp-rated condenser a a 4-zone system with disconnect then 12-2 from condenser to each indoor handler.

    Question is, would i have to pass all 4 12-2 wires through conduit into soffit and then unto rest of the house?

    • Unless your unit calls for it, 12/2 it is overkill for going from the outdoor unit to the indoor units. Most brands require 14/4. Depending on code in your area, you should not need to run the wire through conduit unless this is a commercial installation.

  • The out side unit specifies , max breaker size at 20 amps. My questions is that 20 amp circuit gtoing to power both inside and outside unit or do I have to have two different circuits, one for inside unit and one for outside unit? The system i have is 18000 btu heat and AC.

    • It depends on your specific unit. Most mini splits only require power to the outdoor unit. Then, wiring is run from the outdoor unit to the indoor unit.

          • This is what I got to install my system from LG. I got 1 20 amp circuit in the main panel. I got a a romex 10-3 wire between the main panel and a outside fuseless break box. I got a a whip between the outside box and the compressor unit. From the compressor to each of the airhandlers I installed a 14-4 soft cable (make sure it’s not solid wire). It was difficult to find and get the required 14-3 cable.

  • Great electric advice, THANKS! Planning a system into a ‘50s house, with 4 indoor air handlers and one condenser. Questions: 1. Recommend / must use a GFCI at the main breaker? 2. Do most installs of 4 indoor units draw their power off the outside unit (vs. making a separate electric run to the main breaker box. )? 3. Are the indoor units just basically low current devices – small fans & condensate pumps (no electrical heating elements, etc.), OK to run 4 on a single run of 14/2 wire ? 4. Most indoor units, if wired separate from the outside unit, call for a 15 amp breaker. If the external unit calls for 40 amps and you run 14/2 wire from that outdoor unit to power the 4 indoor units, does the outdoor unit have its own internal breaker or current limiter built in, so in the event any of the 4 internal units start to fail, power to them is rapidly cut off as the draw on that line approaches 15 amps (vs the much more beefy 40 fed to outdoor unit)? 5. Can the typical indoor cassette mount flush within a 16” (and/or 20”) OC joist hard ceiling? 6. When mounting into a hard ceiling do you typically mount to the joists or suspend from the roof rafters? 7. Are cassettes sufficiently sealed / fire rated such that you can pile 32” of blown in fiberglass insulation directly on top of them without heat or fire issues? Thanks!

  • How far can you run the condensing lines from the outside unit to the inside unit ? Is 20′ to much ?

  • Is it ok to run 12/3 solid core wire with a double pole 15 amp from the breaker box to the disconnect, then run 14/3 stranded from the disconnect to outside and inside unit. 14/3 stranded is hard to fine and expensive. I have a 75 ft run from breaker to disconnect and only 30 ft from outside to inside unit.

    • Exact wire specifications depends on your units needs. I would not recommend using 14/3 from the disconnect to the unit. You should use an electrical whip designed to go from the disconnect to the unit. These are usually a heavier gauge and weather sealed. For the outside unit to the inside unit you should use 14/4 mini split wire.

  • Hi, I’m not an electrician so what to make sure I don’t cause an issue

    We have two Mitsubishi Mr. Slim units; one upstairs apartment and one downstairs. My unit upstairs has been working fine and then the next day it wouldn’t turn on. I noticed at the shut off/disconnect box, the downstairs unit on/off switch setting was different from my unit. Although, not sure what signifies on or off.

    In any case, I pulled my switch out and turned it upside down and my unit works now and my switch now looks like the downstairs switch. Since I’m not an electrician, if my unit didn’t work when the switch was in and by turning it upside down and now it works, would this cause an electrical issue? Meaning, even though my unit was working before I flipped the switch (turned it 180 degrees) is it possible the switch had nothing to do with it failing? The reason I’m confused is the neighbors nor I changed (flip) the switch.
    Its possible someone snuck in the backyard and flipped the switch. So would that be the only way the unit didn’t turn on…someone had to have flipped the breaker? Or can the unit work no matter if the switch is flipped on or off? Or it can only work if its on and never works when off? Just want to make sure I don’t cause an issue by flipping the switch

      • Thanks Mickey! Since it was not working and by flipping the switch and it works now, only way for it to not work someone had to have flipped it?

  • Hi, I am installing a Split Duct unit in my house can I install the outdoor unit on the exterior wall “above” the height of the indoor unit ?

  • I want to install a mini-split system for cooling in my house to supplement the existing central AC which doesn’t work well on the top floor due to a lot of glass and a lot of sunshine. Getting 240V to the location is not easy and looks like it is going to be expensive due to the existing wiring. The area I need to cool is around 500 sqft and I’m wondering if I should just go with a low voltage system given the small area. Thoughts? Any negatives of going this route vs 240? Thanks

  • Very good information, I have one question: I am planning to install an 18,000 BTU Mitsubishi ductless air condition. The distance from the panel to the outside disconnect box is approximately 70 ft the specs for the unit says 20 Amps max , 220 Volts. Should I use a 12/3 or 12/2 romex wire from the panel to the disconnect box? (If understood correctly 12/2 is the one because you do not use the neutral wire) -thanks

  • I have 10-2 w/gnd wired to outdoor disconnect box, which means I would wire the whip’s ground and neutral to the supply ground wire in the disconnect box.

    Is this code-acceptable, or will I need to have 10-3 w/gnd from house breaker box to outdoor disconnect?

  • My upstairs unit cannot he a straight run back to the compressor/controller. I had an electrician come in and make the run to code which required the wiring to be spliced because of the run. Now the unit will power on and shut down in under a minute. Is there a specific type of splice that needs to be done or does the splice need to be soldered? Thanks

  • Is it okay to use a mini-split ceiling cassette with a 115V condenser? If not can the blower motor be switched with a 115V blower motor?

  • Can you run the wires from the outdoor unit to the indoor unit in the same conduit on a commercial job without causing any problems as long as all the wires are rated the same voltage

  • Hello. My Mini Split calls for 20 amps, 220 volts. If I run one line to my mini split that is 12-3 gauge from a 20 amp double pole breaker, is there room for me to add an identical mini split to a separate disconnect box in the future? Everything would be identical, same unit, same location, separate disconnect.

  • I am installing a 30k btu lg air mini split with an 18k cieling cassette and a 12k wall unit. I am going to wire a 10/2 from panel to disconnect to outside unit, do I need another wire to supply power to the indoor units or will it recieve all the power from the outside? So all the power I need for these units is whay goes to outside unit?

    • The indoor units receive power from the outdoor unit. You need to run 14/4 from each indoor unit back to the outdoor unit.

  • I am installing an 18000 BTU Mitsubishi mini split in the room above my garage. I asked the builder of the house to prewire for the minisplit. Now that the house and the bonus room are complete I checked and the builder only ran a 12-2 wire (2 insulated wires and a bare ground). Can I use this wire to run the required 230V circuit with a 20 Amp breaker. I thought that I needed 3 insulated wires and a ground??? Many thanks for your answer.

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