• 4 min read

What are AC and DC Disconnects and Why Do You Need to Use Them?

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AC and DC disconnects are essential components necessary for placing a solar panel system on your roof and connecting it to your home. 

An AC disconnect separates the inverter from the electrical grid. In a solar PV system it’s usually mounted to the wall between the inverter and utility meter, and can be a standalone switch or a breaker on a service panel. DC disconnects are switches that can interrupt the flow of DC (direct current). 

Installing AC and DC disconnects properly will ensure that your customer’s home  is safe while also allowing incoming power to be quickly shut off if necessary.

The majority of building codes across the United States require these disconnect switches to be in place. This makes it important to understand how AC and DC disconnects work.

What Do AC and DC Disconnects Do?

The primary purpose of these disconnect switches is so that you can shut off the incoming flow of power from your solar panels. Here is what a typical solar panel system looks like and where to find the disconnects:

AC disconnects and DC disconnects for solar panelsPhoto Credit: Upstate Solar Solutions

DC Disconnects: The DC disconnects (sometimes referred to as the PV disconnects) are placed between the solar panels and the inverter or, in many cases,  built into the inverter.

Inverter: The inverter is the piece of equipment that switches incoming power from DC (direct current) to AC (alternating current) so that your home can use the power. An inverter is needed because the power generated by solar panels is DC (direct current), but homes are wired for AC (alternating current).

AC Disconnects: After power goes through the inverter, it comes out as AC (alternating current). To protect the home in case of emergency, like a fire, AC disconnects are installed after the inverter. AC disconnects are typically mounted on the exterior wall of a home near the electric meter.

Why Are AC and DC Disconnects Necessary?

There are 5 main reasons why you should have AC and DC disconnects on a solar panel installation:

  1. AC and DC disconnects are required by local ordinances and building codes. In addition, some jurisdictions using newer editions of the National Electric Code now require rapid shutdown capabilities, which is essentially an electronic DC disconnection that can take place at the modules or within a few feet.
  2. In the event of a fire in or around a customer’s home, using the AC disconnects to stop the inflow of power can lower the spread of fire and prevent the threat of electrocution to those entering the home.
  3. In the event of severe weather, such as tornadoes, hurricanes, or severe electrical storms, a customer will be able to disconnect their system at the DC disconnects to lower the chance of weather causing damage to their inverter and the home’s interior wiring.
  4. In the event of a flood, being able to shut power off is critical. Both AC and DC disconnects should be used at this time.
  5. If electric company crews are doing work in the area, such as replacing electrical lines or installing transformers, being able to disconnect your solar system from the grid is an important safety feature.

Sizing your AC and DC Disconnects

Disconnects come in a number of sizes, from 30amp up to 800amp, so proper planning  is necessary to determine which disconnect sizes you need.

To know which size is necessary, you’ll want to know the size and power output of your PV system. If you’d like to design a system by hand, here are a few variables you’ll need to consider:

  1. Voltage
  2. Circuit load
  3. Amps/breaker size
  4. Wiring and cable sizes

These components come together to determine the overall load size, which determines the disconnect sizes you need. Once you’ve designed the system, you’ll then need to submit your designs for permitting.

If all this sounds intimidating, don’t worry, Aurora can do a lot of this work for you. Using irradiance mapping, shade analysis, and LIDAR, Aurora can design the optimal system and pick out the best disconnects for you.

Standing out to your solar customers

For homeowners, having a professionally designed solar system is about safety and savings. AC disconnects and DC disconnects are a crucial safety feature that can help you sell a homeowner on the solar panel system you’re building for them. Additionally, by sizing your disconnects properly, you can make sure you’re giving the homeowner the best price for their needs.

AC/DC disconnects are just one piece of the BOS (balance of system) components you’ll need for a successful solar installation. You can learn about some of the other components and how you can save customers even more money in this post: The Basic Principles that Guide PV System Costs.