What Is a Single-Line Diagram for Net Metering?
TL;DR
A single-line diagram is a simplified schematic showing how your panels, inverter, breakers, and meter connect, and it must be signed by a licensed professional electrical engineer before your distribution utility will approve net metering.
A single-line diagram (SLD) is a simplified electrical schematic of your solar system, and your distribution utility will not process a net metering application without one signed by a licensed professional electrical engineer (PEE). It’s one of the required technical documents alongside the Certificate of Compliance, and it’s also one of the more common reasons applications get sent back for correction. This guide covers what the SLD is and why it matters, not how to draw one — that’s PEE work.
What does a single-line diagram actually show?
It shows how your system’s components connect electrically, drawn as a single line per circuit instead of every individual wire. A typical residential SLD includes:
- Panel array, grouped into strings
- DC disconnect and combiner points
- Inverter (or inverters, if more than one)
- AC disconnect
- Main breaker panel and where the solar breaker taps in
- The utility meter and point of interconnection
Component ratings — conductor sizes, breaker amperages, inverter output — usually appear as labels next to each element. A reviewer at your distribution utility or the DOE uses this to check the design without needing to inspect the physical install first.
Why does net metering require a PEE-signed SLD?
Because the diagram represents a claim about how your system interacts with the grid, and only a licensed PEE is authorized to make that claim formally. Distribution utilities like Meralco use it to verify the system won’t create unsafe backfeed conditions, that protective devices are sized correctly, and that the interconnection point matches what their engineers expect to see. This is the same logic behind why final electrical sizing needs a PEE — it’s a licensing requirement under the Philippine Electrical Code, not installer preference.
How the SLD fits into your net metering application
The SLD is submitted alongside your other technical documents as part of the net metering application process. It typically needs to reflect the as-built system, meaning it’s finalized after installation, not just at the design stage. Some installers draft a preliminary SLD for permitting, then issue a revised, as-built version once the system is physically wired, since site conditions occasionally force small changes from the original plan.
Why mismatches between the SLD and the actual install cause rejections
Reviewers compare the signed diagram against what’s physically installed, and a mismatch is one of the fastest ways to get bounced back. Typical triggers:
| Mismatch | Why it flags |
|---|---|
| Extra panels added after signing | Changes system capacity beyond what was reviewed |
| Different inverter model installed | Output characteristics and protection settings may differ |
| Breaker size changed on-site | Protection scheme no longer matches the approved design |
| String configuration changed | Voltage and current at the inverter no longer match the diagram |
None of these are necessarily unsafe on their own, but the utility has no way to confirm that from paperwork that no longer reflects reality. If anything changes after your PEE signs off, get the diagram revised and re-signed before you submit, rather than hoping the reviewer doesn’t notice.
Who to talk to if your SLD gets rejected
Go back to your installer first, since they coordinate with the PEE who signed the original document. A rejection usually means either the diagram needs a technical correction or the installed system needs to be brought back in line with what was approved. Either way, this is licensed engineering and electrical work — not something to troubleshoot yourself. Understanding what net metering costs helps you budget for a possible re-submission fee if a correction round becomes necessary.
Frequently asked questions
What is a single-line diagram in solar net metering?
It's a simplified schematic that shows how your solar system's major components connect electrically: panels, combiner or disconnect, inverter, breakers, and the point where the system ties into your house wiring and the utility meter. It's a wiring map, not a full construction drawing.
Who is allowed to sign a single-line diagram?
A licensed professional electrical engineer (PEE) must sign it. Some distribution utilities also accept a registered master electrician (RME) signature on related documents, but the SLD itself is PEE work because it's treated as an electrical engineering document.
Can I draw my own single-line diagram?
You can sketch one to understand your own system, but it won't be accepted for net metering unless a licensed PEE reviews it, corrects it to match Philippine Electrical Code conventions, and signs it. Utilities check for the PEE's license number and seal.
What does an SLD show that a site photo doesn't?
A photo shows what's on the roof. The SLD shows the electrical logic behind it: how many strings feed the inverter, where the DC and AC disconnects sit, breaker and conductor ratings, and how the system ties into the panel board and meter. Reviewers use it to check the design without visiting the site.
Why do SLD mismatches cause net metering rejections?
If the as-built system doesn't match the submitted diagram, the utility can't verify what it's actually connecting to the grid. Common triggers are added panels, a swapped inverter model, or a different breaker size than what's on the signed diagram.
Does the SLD affect how much my net metering costs?
Not directly. The diagram itself doesn't add to your processing fees, but if it's inaccurate and gets bounced, you pay for a corrected version and lose time. See our breakdown of what net metering costs for the fees that do apply.