Solar Interconnection Diagram: Template and Examples

Every grid-tied solar installation needs an interconnection single-line diagram before the utility will turn it on. The drawing tells the utility's plan reviewer that your install is safe, code-compliant, and won't backfeed dangerous current onto a de-energized line. Get it wrong and your application bounces; get it right and approval is usually a formality.

This article covers what every interconnection SLD must show, the NEC code clauses behind those requirements, and three worked examples: a residential string-inverter system, a commercial microinverter system, and a hybrid PV + BESS install. Free templates linked at the end.

What utilities require in the SLD

Specific requirements vary by utility (your AHJ may add more), but every utility expects to see the following on the diagram:

1. Utility service entrance. Voltage, phase, amperage. For residential this is typically 120/240 V split-phase 200 A.
2. Main service disconnect. Rated breaker or fused disconnect with amperage and AIC rating.
3. Utility-accessible AC disconnect for the PV system. Visible, lockable, labeled. Some utilities require this even if NEC doesn't (NEC 690.13 only requires a PV disconnect, not necessarily utility-accessible).
4. Inverter(s). Make, model, AC and DC ratings. UL 1741 SA / IEEE 1547 listing called out.
5. PV array. Number of modules, module make/model, total DC kW.
6. DC disconnect. Required between modules and inverter (NEC 690.15).
7. OCPD (overcurrent protective device). The breaker on the AC side, sized per NEC 705.12 (120% rule for backfeed at the bus, or supply-side connection per 705.11).
8. Grounding electrode conductor (GEC). Show the bond between the inverter and the grounding system. NEC 690.47.
9. Rapid shutdown initiator (for rooftop systems). NEC 690.12. Usually a labeled switch at the service entrance.
10. Labels. Each labeled element should match field labels installed at the equipment. NEC 690.13(B), 690.56.

Example 1: Residential string-inverter PV (8 kW)

The most common configuration: roof-mounted PV array → DC combiner → string inverter → AC disconnect → main service panel backfeed breaker.

• Array: 20× 400 W modules in 2 strings of 10 (8 kWp DC)
• Inverter: 7.6 kW string inverter (e.g. SolarEdge, Enphase IQ8 combiner, SMA)
• DC disconnect: integrated in the inverter
• AC disconnect: 30 A fused disconnect, utility-accessible, on the exterior wall next to the service meter
• Backfeed breaker: 40 A in the main panel (sized for inverter continuous output × 1.25 per NEC 705.60)
• Main panel bus rating: 200 A — works under the 120 % rule because (200 × 1.20) − 200 = 40 A allowable backfeed
• Rapid shutdown: required, labeled at the service entrance per NEC 690.12

Backfeed breaker sizing (NEC 705.60 + 705.12)

Two calculations matter:

1. OCPD continuous current sizing: I_OCPD ≥ 1.25 × I_inverter_continuous

For a 7.6 kW inverter at 240 V: I = 7600 / 240 = 31.7 A, so I_OCPD ≥ 39.6 A → 40 A breaker.

2. 120 % rule for backfeed location: (Bus rating × 1.20) − Main breaker ≥ Backfeed breaker

For a 200 A bus with 200 A main: (200 × 1.20) − 200 = 40 A — exactly at the limit. A 40 A backfeed is the maximum allowed at this bus.

If the math doesn't work (e.g. larger PV system on a 200 A bus), you have three options:

• Use a supply-side connection (line-side tap before the main breaker) per NEC 705.11
• Use a derated main breaker (replace the 200 A main with a 175 A or 150 A main)
• Upgrade the panel to a higher-rated bus

Example 2: Commercial microinverter PV (60 kW)

Microinverter systems replace one big string inverter with many small ones, one per module. The SLD is similar but with these differences:

• No DC disconnect (each microinverter has integrated DC isolation — NEC 690.15 satisfied at the module)
• Multiple AC trunk cables, each landed in a sub-feed combiner
• Each combiner has its own OCPD before tying back to the main panel

The interconnection SLD shows one representative microinverter and notes "qty 150 typical" rather than drawing every one. The combiners are explicit. The utility-accessible AC disconnect is between the combiner output and the service.

Example 3: Hybrid PV + BESS (480 V three-phase, 100 kW PV + 250 kWh battery)

Battery-tied systems are increasingly common (utility rate arbitrage, demand-charge mitigation, backup power). The interconnection SLD adds:

• BESS DC bus + battery rack: kWh capacity, battery chemistry, voltage range
• Bidirectional inverter / PCS: kW rating, modes (grid-tie, islanding, self-consumption)
• BESS AC disconnect: between PCS and main bus, often co-located with utility disconnect
• Automatic transfer switch (ATS), if the BESS provides backup during outages
• Critical-load sub-panel, if backup is partial (only essentials)
• NEC 706 references for energy storage systems
• Anti-islanding listing: PCS must be UL 1741 SA certified for grid-interactive operation

This is the same topology shown on the SmartSLD homepage demo — utility service → main → meter → 480 V switchgear, with a PV inverter on one branch and BESS on another via a bidirectional converter. Open the demo to see it live.

NEC clauses to cite on your drawing

The plan reviewer wants to know you've thought about the code. Putting these annotations on the diagram itself reduces back-and-forth:

• NEC 690.12 — Rapid shutdown
• NEC 690.13 — Building PV disconnects
• NEC 690.15 — Disconnect requirements for DC PV circuits
• NEC 690.47 — Grounding
• NEC 690.56 — Identification of PV systems
• NEC 705.11 — Supply-side connection
• NEC 705.12 — Load-side source connections (120 % rule)
• NEC 705.60 — Circuit sizing and current
• NEC 706 — Energy storage systems (if BESS)
• NEC 480 — Battery bank installation (if BESS)
• NEC 250.166 — Grounding electrode conductor sizing
• UL 1741 SA / IEEE 1547 — Inverter grid-interactive listing

Common reasons utilities reject interconnection SLDs

• No utility-accessible AC disconnect shown
• Backfeed breaker location violates 120 % rule and no supply-side connection proposed
• Missing make and model of inverter (utilities check the UL 1741 SA listing themselves)
• Rapid shutdown not shown or not labeled
• Grounding electrode conductor not clear
• Wire sizes / OCPD sizes not annotated
• System voltage doesn't match the panel rating

Templates

Open any of these in the editor and modify for your specific install:

• Residential 8 kW PV — string inverter, 200 A service, line-side connection
• Commercial 60 kW PV — microinverters, 400 A service, load-side connection
• Hybrid PV + BESS — 100 kW PV + 250 kWh battery, 480 V three-phase service

The homepage demo at smartsld.com is the hybrid template. Use the AI prompt feature to generate a variation tailored to your system size.

FAQ

Do utilities accept SLDs drawn in any software?

Most accept any clean, readable format — PDF, PNG, or DXF. A few large utilities have specific format requirements (PG&E, ConEd). Check your utility's interconnection application portal first.

Do I need a PE stamp on my interconnection SLD?

Depends on the utility, system size, and state. Most residential systems under 25 kW don't require PE stamping. Larger or commercial systems often do.

What about microgrid interconnection?

Microgrid interconnection adds an ATS, critical-load distribution, and possibly islanding controls. The SLD becomes more complex but the same component rules apply.

Can AI generate an interconnection SLD for my specific system?

SmartSLD's AI agent can. Prompt example: "8 kW residential PV with single-phase string inverter, 30 A AC disconnect, 40 A backfeed breaker, 200 A main service" generates the full SLD with NEC-compliant labeling. Cross-check the output against your utility's checklist before submitting.

Related

• How to Draw a Single-Line Diagram (Complete Guide)
• 200 A Service Single-Line Diagram Template
• SLD Symbols Cheat Sheet

Got a utility rejection because of something we didn't cover? Send it to [email protected] — we'll update the article.