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 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 to 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

Before we take you through the steps on wiring a mini split system, we’re going to clarify some common questions about your mini split wiring.

1. What size wire do I need for a mini split? 

For most ductless mini-splits, the right wire is a 14/4 stranded conductor cable. Mini-split wires are used to connect the outdoor compressor unit with the indoor evaporator unit, delivering electricity and control signals.

A 14/4 stranded cable provides two 14-gauge conductor wires for power, one communication wire and one ground wire. The ground wire is essential for safe operation, preventing damage to the air conditioner and protecting your family, which is why going with 14/4 is always better than 14/3.

2. When do I use a 10/2 or 10/3 for mini splits?

When installing a mini-split air conditioner, it’s vital to choose cable that’s large enough to handle the current your system requires. For ample spaces and significant heating/cooling, some homeowners choose a mini-split with 36,000 BTU capacity. This type of system can require a 30-amp circuit, so you would need 10-guage wire to handle the current. Every unit will list its amp draw and the wire choice will vary based on that.

What do 10/2 and 10/3 wire numbers mean? The first number is the thickness in AWG (American wire gauge). Don’t forget that in AWG, smaller numbers mean thicker wires. So a 14-gauge wire is medium sized, 12-gauge would be a little bigger, and 10-gauge is the biggest wire you’re probably going to need for a mini-split.

The second number is the amount of connectors the wire has. A 10/2 wire has two connectors, the black and white, both hot/lead wires as well as a ground wire. On the other hand, 10/3 wires have three connectors, black, white and red plus a ground wire. 

For additional guidance, check out: Wire Size Guide: What Size Wire Do I Need?

With any electrical project, be sure to check with a licensed electrician and verify the requirements of your local codes.

Now that we have that clarified, 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 volts* 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 some 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

To meet the code, you must have a shut-off 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.