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Bogdan is the Sr. Content Marketing Manager at Aurora Solar.

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

Bogdan ZlatkovBogdan Zlatkov

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

Installing AC and DC disconnects properly will ensure that the home of your customer is kept 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, so it’s important to understand how they work and why they’re needed. 

What Do AC and DC Disconnects Do?

As the name implies, 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 the disconnects are located:

AC and DC disconnectsPhoto 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, are 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, AC disconnects are installed after the inverter. AC disconnects are typically mounted on the exterior wall of the customer’s home near the electric meter. 

Why Are Disconnects Necessary?

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

  1. They 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 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 variety of sizes, from 30amp all the way up to 800amp, so proper planning of your system is necessary to determine which disconnect sizes you need.

In order 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

All of these components come together to determine the overall load size, which will determine 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 actually do a lot of this work for you. Using irradiance mapping, shade analysis, and LIDAR, Aurora can actually design the optimal system and pick out the best disconnects for your needs.  

Standing out to your solar customers

For homeowners, having a professionally designed solar system is about safety and savings. AC/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.

Bogdan is the Sr. Content Marketing Manager at Aurora Solar.

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