Avila Solar Drafting handles the electrical and structural engineering behind a San Antonio solar submittal. The detail that defines this market: two separate authorities apply two different PE-seal tests to the same project, with two different voltage breakpoints. Getting that wrong means either an unnecessary seal or a missing one, and both cost a review cycle. We settle which tests apply before drafting.
Key takeaways
- Two PE tests, two breakpoints. The city’s electrical trigger turns on 250 volts. CPS Energy’s turns on 150 volts to ground. Neither one is “the San Antonio threshold.”
- The structural trigger is conjunctive. More than 6 lbs per square foot and a roof slope under 4:12 — both conditions, not either.
- Every commercial building requires Texas PE calculations, unconditionally — no weight or slope threshold applies.
- CPS Energy publishes no distance rule for the AC disconnect. The 10-foot figure people carry in from Dallas or Houston does not belong here.
- San Antonio sits on the 2024 IBC and IRC — a full cycle ahead of Dallas and Houston — with the 2023 NEC.
Two authorities, two PE-seal tests
This is the single most misreported fact about designing solar in San Antonio, and the reason is simple: both tests sound alike until you read the voltage.
The city’s test sits in San Antonio City Code Sec. 10-8(b)(6). Electrical plans must be sealed by a professional engineer licensed or registered with the state where equipment on the customer side of the CPS Energy point of delivery is rated over 600 amps at 250 volts or less, or over 400 amps at greater than 250 volts — plus any system above 600 volts, or wherever the Texas Engineering Practice Act independently requires it.
CPS Energy’s test sits in its Distributed Generation Manual, Ninth Edition, revised May 1, 2024. There, drawings must be signed and sealed by a licensed engineer when the system is over 600 amps at 150 volts to ground or less, and/or 400 amps at 150 volts to ground or greater.
Same amperage numbers, different voltage basis — 250 volts for the city, 150 volts to ground for the utility. A project can clear one test and trip the other. Any sentence that merges them into a single San Antonio threshold is wrong for one authority, so we name the authority every time and check both at intake.
One correction worth putting on the record, because it circulates widely: the 50 kWac line in CPS Energy’s manual is not a PE-seal threshold. It governs certified-equipment eligibility and insurance. Relying on it to skip a seal is how a set gets returned. General background on stamp triggers is in PE stamp triggers.
The structural trigger, read precisely
San Antonio’s structural requirement is one of the clearest published anywhere in Texas, which makes it worth quoting rather than paraphrasing. Under Information Bulletin 153, single family, R-3, duplex and townhome buildings require engineering calculations from a Texas-licensed engineer for roof-mounted arrays where any of the following occur:
- The array weighs more than six pounds per square foot and is installed on a roof with a slope of less than 4:12. Both conditions together — a heavy array on a steep roof does not trigger it, and a light array on a low slope does not either.
- Two or more existing applications of any type of roof covering are encountered. This is why the overlay count belongs in the site survey rather than being discovered on installation day.
- A new structure — trellis, patio cover, canopy, carport or similar — is built to support the PV system and would otherwise be exempt from a building permit under the Chapter 10 city amendments and the Unified Development Code. That qualifier is part of the rule and is frequently dropped when the trigger is quoted second-hand.
And on the commercial side there is no threshold at all: all commercial buildings require engineering calculations from an engineer licensed and registered in the State of Texas. For EPC firms that is the whole answer — scope the seal into every commercial San Antonio project rather than testing for it.
A separate bulletin covers arrays on new supporting structures: Information Bulletin 405, “Solar Pergolas,” dated August 17, 2023, issued after Texas HB 3526. It calls for sealed plans from a Texas-licensed structural engineer for a new pergola carrying PV, or a PE-sealed load letter confirming an existing one can take the added weight, along with a foundation and frame letter and its own inspections — and it states that a solar pergola may not double as a carport, garage or storage structure. Solar structural load calculations covers the analysis behind all of this, and we hold seals in-house through engineering stamps.
The CPS Energy disconnect, and the rule that is not here
CPS Energy’s Distributed Generation Manual requires a visible load-break disconnect switch, installed to CPS Energy’s specification and at the generation owner’s cost, readily accessible to CPS Energy personnel and of a type that can be secured in the open position by a CPS Energy padlock. Elsewhere the manual describes a manual disconnect device with a visual break appropriate to the voltage level — a disconnect switch, draw-out breaker or fuse block — accessible and lockable open.
What is not in any CPS Energy document is a distance. Oncor requires the disconnect within ten feet of its meter across the Metroplex, and CenterPoint applies the same ten-foot rule in Houston. CPS Energy publishes no equivalent footage. A designer who carries the ten-foot rule into San Antonio is applying another utility’s requirement, and a designer who assumes no rule exists because no distance is published is missing the padlock and accessibility requirements that do. We specify a device that satisfies what CPS Energy actually asks for and place it where the meter geometry and the utility’s access needs put it.
On thresholds: CPS Energy allows certified equipment and equipment carrying an approved test label for systems up to 50 kWac, with no insurance certificate required at or below that figure. Above 50 kWac up to 1 MWac a screening study applies; at 1 MWac and above, ERCOT and PUC registration enter the picture. Those bands shape the interconnection scope, not the sealing question.
Sizing to a San Antonio climate
String length is bounded by the cold end — open-circuit voltage rises as temperature falls, and Article 690.7 requires maximum system voltage to be computed from the module’s temperature coefficient against the lowest expected ambient, capped at 600 volts on one- and two-family dwellings. Conductor ampacity is corrected at the other end, against summer conditions.
The published basis we work from is the National Weather Service 1991–2020 normals for San Antonio International Airport: January averages 63.3°F high and 41.0°F low; July 94.9°F and 74.7°F; August 96.0°F and 74.9°F, with an annual mean of 69.6°F. San Antonio’s official record low is 0°F, on January 31, 1949 — and that figure is context, not a design input. Sizing a modern array to a 1949 reading strands capacity on every string for the life of the system. Our worked method, with examples, is on the solar string sizing page.
What manufacturer sizing tools will not do for you: apply the 600-volt dwelling ceiling, choose a design temperature for your address, or run the Article 690.8 and 690.9 conductor and overcurrent checks a reviewer will run. A tool gives a string length; a plan set has to give a defensible calculation.
The 2024 I-codes change the structural reference
San Antonio adopted the 2024 IBC and 2024 IRC alongside the 2023 NEC, effective May 1, 2025, under Ordinance 2025-01-30-0075, with city amendments in Chapter 10. Dallas and Houston both remain on 2021 building and residential codes.
For structural design that gap is not cosmetic. Moving from the 2021 to the 2024 I-codes moves the referenced ASCE 7 edition forward, which is what actually governs how wind and seismic loads are determined. A set drawn for a 2021-IBC city and reused in San Antonio can carry the wrong load basis while looking perfectly complete. We confirm the referenced edition per project and pull site-specific values rather than publishing a citywide wind number that would be wrong for some addresses in Bexar County. The deliverable this produces is described on San Antonio solar plan sets, and the submittal route on San Antonio permit design.
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.
San Antonio Solar Design FAQs
When does a San Antonio solar project need a PE seal?
Two tests apply. The city requires sealed electrical plans over 600 amps at 250 volts or less, or over 400 amps above 250 volts, plus any system above 600 volts. CPS Energy requires sealed drawings over 600 amps at 150 volts to ground or less, and/or 400 amps at 150 volts to ground or greater. Structurally, IB 153 triggers engineering calculations on its own conditions, and all commercial buildings require them unconditionally.
Is the 6 psf structural trigger an “or” or an “and”?
An and. IB 153 triggers engineering calculations where the array weighs more than six pounds per square foot AND is installed on a roof with a slope of less than 4:12. Two or more existing roof coverings, or a new supporting structure that would otherwise be permit-exempt, are separate independent triggers.
Do commercial solar projects in San Antonio always need engineering?
Yes. IB 153 states that all commercial buildings require engineering calculations from an engineer licensed and registered in the State of Texas. There is no weight or slope threshold on the commercial side.
How far from the meter does the AC disconnect have to be in San Antonio?
CPS Energy publishes no distance. Its Distributed Generation Manual requires a visible load-break disconnect installed to CPS Energy’s specification, readily accessible to CPS Energy personnel and capable of being secured open by a CPS Energy padlock. The ten-foot rule belongs to Oncor and CenterPoint, not to CPS Energy.
Does a system under 50 kW skip the PE seal for CPS Energy?
No. The 50 kWac figure in CPS Energy’s manual governs certified equipment eligibility and insurance, not engineer sealing. CPS Energy’s sealing test is amperage-based, and a smaller system can still cross it.
What temperature do you size strings to in San Antonio?
The site’s expected extreme minimum against the module’s temperature coefficient per Article 690.7, capped at 600 volts on one- and two-family dwellings, with ampacity corrected against summer conditions. NWS 1991–2020 normals for San Antonio International put January at 63.3°F high and 41.0°F low, and August at 96.0°F and 74.9°F. The 1949 record low of 0°F is context, not a design basis.
Does San Antonio’s 2024 I-code adoption change my structural design?
It can. Moving from the 2021 to the 2024 IBC and IRC moves the referenced ASCE 7 edition forward, and that reference is what governs how wind and seismic loads are determined. A set drawn for Dallas or Houston, both still on 2021 codes, may carry the wrong load basis for San Antonio.
Scope a San Antonio project with a designer
Engineering scope is quoted rather than ordered from a menu — a low-slope commercial roof under the unconditional commercial rule and a straightforward composition-shingle retrofit are not the same job.
Or start a standard set at my.avilasolar.com. Avila Solar Drafting LLC, 11995 SW Walker Rd, Beaverton, Oregon · 971-410-0655 · info@avilasolar.com.