Avila Solar Drafting handles the electrical and structural design behind a Dallas solar submittal — conductor and OCPD sizing, cold-temperature string sizing, attachment and load path, and the AC disconnect configuration Oncor will accept. Where the scope triggers a Professional Engineer’s seal, we handle that in-house rather than sending you to find one.
Key takeaways
- Oncor will not accept a molded-case breaker as the visible load-break disconnect — a device selection made at the design stage, not on site.
- String sizing in Dallas is governed by the ASHRAE extreme annual mean minimum temperature for the project site, not a regional rule of thumb.
- Dallas enforces the 2021 IBC and IRC, which reference ASCE 7-16 for wind and snow load determination.
- Manufacturer string-sizing tools do not apply the 690.7 600-volt dwelling limit and do not choose your design temperature.
- PE stamps are handled in-house, so a triggered stamp doesn’t restart your schedule.
The Oncor disconnect decision, made at the drawing stage
Most of the Metroplex is Oncor territory, and Oncor’s disconnect requirements are specific enough that getting them wrong is a design error, not a field fix.
Oncor’s residential and small commercial project requirements, revised May 1, 2025, state that a single separate visible, lockable, labeled AC disconnect must be located between the meter and all sources of distributed generation, and that it “must be located on an ACCESSIBLE, EXTERIOR wall within 10 feet of the Oncor Meter.” The device must have an external handle, be lockable, and remain accessible at all times. Beyond 10 feet or out of the meter’s line of sight, a placard is required.
The requirement that catches people is this one, verbatim: “Molded-case breakers are NOT considered acceptable VLLDs.” A molded-case breaker is a reasonable-looking choice on a single-line diagram and it will not pass. We specify an acceptable device and place it correctly on both the site plan and the single-line diagram, so the question never reaches a field crew.
Cold-temperature string sizing for a Dallas site
Maximum string length is set by the coldest expected cell temperature, because open-circuit voltage rises as temperature falls. Article 690.7 requires the maximum PV system voltage to be calculated using the module’s temperature coefficient against the lowest expected ambient temperature — and for one- and two-family dwellings, that voltage may not exceed 600 volts. That dwelling limit reads the same under the 2020 and 2023 cycles, so it applies whichever edition your Dallas-area reviewer is enforcing — a question worth settling before drafting, and one we cover on the Dallas permit design page.
The right basis is the coldest ambient the site actually sees — not a record low, and not a regional rule of thumb. Two published references frame Dallas. USDA Plant Hardiness Zone 8b puts the average annual extreme minimum at 15°F to 20°F (2023 USDA map), the closest published proxy for a cold design basis. NOAA’s 1991–2020 climate normals for DFW put the January average low at 36.1°F and the winter average low at 38.2°F — useful context, but averages, not the cold a string has to survive. The all-time DFW record is −8°F (February 1899), and that is not the basis either: designing to a 127-year record strands capacity on every string. The usable number sits between those, it varies across the Metroplex and between stations, and we pull it per project rather than carrying one figure across every Dallas job. Our worked walkthrough, with two full examples, is in solar string sizing.
Three things manufacturer sizing tools reliably don’t do: they don’t apply the 690.7 600-volt limit for dwellings, they don’t choose your ASHRAE design temperature for you, and they don’t run the NEC 2023 690.8 and 690.9 conductor sizing and overcurrent protection checks that the plan reviewer will. The tool gives you a string length; the plan set has to give the reviewer a defensible calculation.
Conductor ampacity on the AC side gets the opposite correction — sizing against the summer 2% design dry-bulb condition, with rooftop conduit ambient adders where the run warrants it.
Structural design: what governs a Dallas array
Dallas enforces the 2021 IBC and 2021 IRC with Dallas amendments, effective May 12, 2023. The 2021 IBC references ASCE 7-16 for load determination, so wind and snow values come from that edition — and both are site-specific values pulled for the project’s coordinates, not citywide constants. We run them per project through the ASCE 7 Hazard Tool rather than publishing a metro-wide number, because a number that’s right for one address can be wrong for another.
What we design and document: attachment type and spacing, the load path from module to rafter, and the calculations where the jurisdiction or the roof condition requires them. Where an array sits on a low-slope roof, adds meaningful dead load, or lands on a structure that wasn’t built for it, the analysis has to be explicit rather than assumed. Solar structural load calculations covers the load taxonomy and how the edition mapping works.
When a Dallas project needs a PE stamp
Stamp triggers are jurisdiction-specific, and Dallas-area cities do not publish a single shared threshold the way San Antonio does with its Information Bulletin 153. In practice, the triggers worth scoping at intake are: ground-mount and carport structures, arrays on low-slope roofs, roofs carrying two or more existing covering layers, added dead load beyond what the existing framing was designed for, structures that were never engineered for a rooftop array, and commercial scopes.
We hold stamps in-house through our engineering stamps service, which means a project that turns out to need one doesn’t go back into a queue while you find an engineer. PE stamp triggers are covered in detail separately, and ground mount plan sets covers the structural scope specific to ground arrays.
What you get, and how it fits your workflow
Electrical and structural design delivered as a coordinated set — single-line diagram, sizing calculations, structural details and attachment schedule — in a submittal-ready PDF package plus source files. For the full sheet-by-sheet deliverable and turnaround tiers, see Dallas solar plan sets.
We guarantee accurate solar plan sets, drawn to the electrical and building code requirements of your specific jurisdiction and designed to pass first-time review.
Dallas Solar Design FAQs
What AC disconnect does Oncor require?
A single separate visible, lockable, labeled AC disconnect between the meter and all distributed generation, on an accessible exterior wall within 10 feet of the Oncor meter, with an external handle, lockable, and accessible at all times. A placard is required beyond 10 feet or out of line of sight.
Why won’t a molded-case breaker pass as the disconnect?
Oncor’s residential requirements state directly that molded-case breakers are not considered acceptable visible load-break disconnects. It’s a device-selection decision that belongs in the design, since discovering it at inspection means a change order.
What temperature do you size strings to in Dallas?
The ASHRAE extreme annual mean minimum design dry-bulb temperature for the project’s location, applied against the module’s temperature coefficient per Article 690.7. We pull it per project rather than using one metro-wide figure, and the resulting maximum system voltage must stay at or below 600 volts on one- and two-family dwellings.
What wind and snow values govern a Dallas array?
Dallas enforces the 2021 IBC and IRC, which reference ASCE 7-16 for load determination. Both wind and ground snow values are site-specific for the project coordinates, so we pull them per project through the ASCE 7 Hazard Tool rather than applying a citywide figure.
When does a Dallas project need a PE stamp?
Common triggers are ground mounts and carports, low-slope roofs, roofs with two or more existing covering layers, added dead load beyond the existing framing’s design, un-engineered supporting structures, and commercial scopes. We scope it at intake and stamp in-house when it’s triggered.
Do you handle both the electrical and the structural design?
Yes — conductor and OCPD sizing, string sizing, grounding and interconnection on the electrical side; attachment, load path and calculations on the structural side, with the PE seal where required.
Scope a Dallas project
Engineering scope is quoted, not ordered off a menu — a low-slope commercial roof and a straightforward composition-shingle retrofit are not the same job.
Call 971-410-0655 to scope a Dallas project with a designer.