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Understanding Permit Plans for DIY Solar Projects

It is very common for a Do-It-Yourself solar installer to get the permit plans drawn up by the distributor or by a third party company. Doing this definitely makes things go smoother when pulling the permit at the city or county building department and these plans also serve as instructions on how to install your system so it is worthwhile to talk about how to interpret them.

Sample page from a solar permit plan
Sample page from a solar permit plan

First, we have to say that looking at the planset does not substitute for reading installation manuals. It is important that you read the installation manuals for your solar panels, solar panel racking system and inverter (or microinverters). There will be a lot of details in those documents that won’t be covered in the plans so don’t treat the plans like the cliff notes you used to get through English class in high school.

Next, you should look over the plans before you submit them to the city or county. Make sure they show all the correct equipment and correct equipment locations. When the inspector comes out to look at your installation, part of their job is to check that everything matches the plans. Look at what the plans say about your main service panel (especially the busbar rating, main service breaker rating, and main service breaker location). If any of that is incorrect, you want to get the plans changed before submitting. Also make sure that there is room on the wall to install the inverter, AC combiner and AC disconnect where they are shown on the plans. Measure your roof area to ensure the layout on the plans will work and the fire code setbacks shown on the plans are really there. If the inspector calls you out on incorrect setbacks after you have installed the system, you will have to move the panels on the roof which will not be fun.

When installing, make sure you follow the plans. Things like the fuse or breaker size must be installed as shown on the plans. You have to get the wire type exact, THWN-2 has different ratings than THWN so it is important to pay attention. You should also use the conduit type that is on the plans, the NEC code and individual building departments have lots of rules about this so it says RMC, don’t try to substitute EMT.  

You do have a little bit of flexibility to use larger wire or larger conduit than what the plans show but never use smaller. If the plans say 10 AWG and there is a sale on 8 AWG, the inspector typically won’t have a problem as long as you make sure you upsize the conduit appropriately. You can also use larger conduit than the plans show and going up one size on the conduit will often make pulling wires a lot easier so it might be worth it.

Finally, if there is anything on the plans that you don’t understand make sure you ask whoever drew them for you. Asking that question will be easier than failing an inspection because you did something incorrectly. can help you every step of the way with your solar project, including plans, permitting, and interconnection.

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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