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Grid-Tied Solar Interconnection Options

If you are installing solar to save money on your electric bill, it is going to be a “grid-tied” system. When we talk about the “grid” we are talking about the electric company’s network of transmission lines and equipment that bring the electricity from the power plant to your house. The “tied” part of “grid-tied” means exactly what you would think it does, you are going to connect your solar power system to that grid. 

The actual point of interconnection is typically your main service panel. This is the point where the grid ends and your home’s electrical system starts. It can generally be said that anything before your main service breaker belongs to the electric company and we call this part of the system the line side or supply side. Anything after your main service breaker belongs to you and we call this the load side because that is where your loads are. A load is anything that uses electricity like your lights, washing machine, air conditioner, etc.

There are a few different ways to make that interconnection at the main service panel and that is the point of today’s article. The simplest method for the do-it-yourself solar installer is a load side connection made with a circuit breaker in your main service panel. This means you are going to add a circuit breaker in your main service panel next to all the circuit breakers that feed your loads and you will connect your solar inverter output to that circuit breaker.

One thing to note about this type of load side connection are that the inverter circuit breaker will need to be as far as possible from your main breaker so you may have to move a few load breakers to make space for it at the end of the busbar that holds all your breakers.  

Another thing you need to know about a load side connection with an inverter circuit breaker is that you have to follow the 120% rule (2014 NEC 705.12(D)(2)(3)(b) or NEC 2017 705.12(D)(2)(3)) where the main service breaker plus 125% of the maximum solar output must be less than or equal to 120% of the busbar rating. You can see our previous article about evaluating your main service panel for solar to understand the math on this but the bottom line is there are times when you can’t make this type of connection without an expensive main service panel upgrade, so let’s look at the other options that are available. 

So, if you are not going to interconnect your solar power system on the load side of your main service breaker, that means you are going to interconnect on the supply side (a.k.a. line side). This gets a little tricky because you are going to tap the wires between the main service breaker and the utility meter. The main service breaker is no longer in between your solar and the grid so your solar circuit so you are losing a layer of protection on the solar output. To account for this lack of protection from the main service breaker, you will need to install a fused AC disconnect within 10 feet of the point of interconnection.     

Tapping the electric company’s wires to make a supply side interconnection is not always allowed by the electric company, especially on residential projects. If this is the case, your electric company may offer an alternative way to make a supply side interconnection using a “meter adaptor” which are common in Southern California. The meter adaptor takes the place of your existing electric meter and provides a place to tap in with the solar. There are many different types of meter adaptors and most electric companies want to supply you with a specific one and they also may want to install it themselves. There also may be rules about having a fused disconnect within 10 feet of the meter adaptor just like if you were tapping the conductors to interconnect. 

No matter how you are making your interconnection, you have to make sure you are being safe. The only way to truly de-energize your main service panel is to pull out the utility meter. If you just turn off your main service breaker, the busbars or wires feeding the main service breaker are still live. Even if all you are doing is putting in the inverter circuit breaker, it is not safe to have the deadfront off the main service panel with any part of the system still live, so pulling off the electric meter is the only truly safe way to do this work. This often requires a phone call to the electric company to have them unlock the meter ring so that the meter can be removed but it is worth the trouble to stay alive.

If all that safety talk scares you, that doesn’t mean you shouldn’t install your own solar. You can always install the system yourself and hire an electrician to make that final interconnection. 

Finally, we understand that a lot of this information can be confusing and there are so many details to worry about in deciding how to make your interconnection so feel free to call the experts at GoGreenSolar.com for help. We know just the right questions to ask to make the determination and get you on your way to a successful do-it-yourself solar installation.  

Author: Harold Tan

I believe clean, renewable energy is key to the evolution of society as a whole. Solar powers our planet, why not harness it to power humanity? Let's power our homes, our work, and our vehicles with solar energy. It begins with raising awareness and encouraging those around us to go green.

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