Part VII: Solar ElectricityChapter 11. Grid-Tied and Off-Grid PV
PV Wiring, Grounding, and Code Basics (When to Hire an Electrician)
The ideas behind a safe PV circuit, and the work that belongs to a licensed electrician.
- Difficulty
- Advanced
- Cost
- Free
Photovoltaic modules are a power source you cannot switch off by killing the house. Light on the glass is enough. The wires between modules can sit at a high direct-current voltage on a cold morning even when the inverter is dark. Grounding, rapid shutdown, connectors, and the bright line between learning the ideas and landing a conductor all follow from that.
This page stays on the learning side of that line. It does not give string lengths, wire gauges, torque values, or a diagram you could build from. Those are a licensed electrician's design, on a permit, for the code edition your inspector uses. Array size is still the bill page. Which box goes on the roof is the layout page. How the rails stay on is the mount page.
Difficulty
- Level
- Advanced
- Time
- Long enough to know what you will not do yourself
- Skills
- Leaving the service panel closed
Cost estimate
Free
The reading is free. The electrician, the permit, and the utility interconnection are the cost of a legal system. They are cheaper than a fire or a lineworker hurt by a backfeed.
Materials
| Item | Qty | Notes |
|---|---|---|
| A licensed electrician who will sign the work | 1 | Some places allow a homeowner to pull a permit on their own house and still expect the same inspection. Ask. Do not guess that a blog post is the allowance. |
| The interconnection rules from your utility | 1 | A system that can run in parallel with the grid needs their agreement. Selling or banking energy takes a contract with them. |
| Listed equipment | Modules, inverter, racking, breakers | The inspector is looking for listings and a design, not for ingenuity. |
The ideas, without the recipe
Series connections add voltage. Parallel connections add current. Too many modules in series, especially when the cells are cold and the open-circuit voltage rises, can exceed what the inverter and the code allow. Too much current can exceed a wire and a connector. The design uses the cold-weather voltage and the hot-weather current, not the pretty number on a warm brochure. You do not need to perform that design to understand why a "it fit on the roof" string is not a design.
Metal frames and rails are bonded so a fault has a path that trips protection instead of waiting in the frame for a hand. Equipment grounding, and the ground-fault protection in the inverter, are that path. They are not a rod you drive and then ignore. Rapid shutdown, required on many rooftop systems, is there so a firefighter can make the array stop presenting a dangerous voltage. Whatever method your system uses has to be listed and has to be the one the permit shows. You do not invent a shutdown.
Connectors that snap together are polarized and they are not all the same inside. Mixing two brands that look alike is a known way to heat a joint until it burns. Disconnecting them while current is flowing draws an arc. Direct-current arcs do not always quit when you wish they would. Cover the modules, follow the inverter's shutdown, and let someone qualified separate connectors. Do not do it under load because you are in a hurry.
The work you hand over
Anything that touches the service panel, a new breaker, a line-side connection, or a conductor that can energize the utility's wires is the electrician's work and the utility's permission. The deadly shortcut is a cord with plugs on both ends, or any jumper into a dryer outlet or a generator inlet, used to "backfeed" a panel. It can energize the lines outside. It can kill a person who thought the neighborhood was dark. There is no careful version of that shortcut. A legal generator or a legal array uses an interlock or a transfer switch that makes it impossible to feed the grid and the backup at once, installed under a permit.
A small off-grid shed that never meets the house wiring is a different circuit and still not a toy. Fuses, a charge controller, and a battery have their own page. The moment a wire from that shed can reach the house panel, you are back in interconnection rules.
If your town allows an owner-builder to pull the permit, the inspection is the same inspection. Listings, clearances, rapid shutdown, and grounding do not relax because you did the labor. If you cannot explain the design to the inspector, you are not ready to install it.
Stop at the service panel
Learn the ideas here, but do not open the panel. Hire the person who will sign the permit.
Ask the utility what interconnection requires
Agreement, a disconnect they can see, and their timeline. Do not energize in parallel as a surprise.
Keep connectors matched and covered until they are ready
One brand, the maker's mates, modules covered before anyone separates them. No live unplugging.
Refuse every homemade tie to the house
No double-ended cord. No dryer outlet. No quiet backfeed. Interlock or transfer equipment, permitted, or the array stays off the building.
Further reading
These links go to outside sources. This book cites them by link and does not copy their words or pictures.
- https://www.builditsolar.com/Projects/PV/pv.htm
- https://www.builditsolar.com/Projects/PV/EnphasePV/ComponentSelection.htm
- https://www.builditsolar.com/Projects/PV/EnphasePV/Mounts.htm
- https://www.builditsolar.com/Projects/PV/EnphasePV/Wiring.htm
- https://www.builditsolar.com/Projects/PV/EnphasePV/Economics.htm
- https://www.builditsolar.com/Projects/PV/EnphasePV2019/Main.htm
- https://www.builditsolar.com/References/pvwiring.htm
- https://www.builditsolar.com/Experimental/PVShading/
General education, not a permit or a stamped design. Follow the safety note in the guide, read the safety disclaimer, and hire a licensed trade when the work requires one.