Electrical Engineering and Design

Most of the electrical engineering on a commercial job is not the part that needs a seal. Load calculations, the one-line, feeder sizing, panel schedules, photometrics and the utility application package are production work, and we do that in-house. What needs a seal gets one, from a licensed Arizona PE we coordinate. This page says where the line falls.

Arizona registers professional engineers through the Board of Technical Registration, and contractor licensing is no substitute for it. We do not hold a PE seal in-house. Where a set has to be signed and sealed we coordinate a registered Arizona PE, hand over the calculations and the model, and let them review, revise and take professional responsibility for it.

Our licenses are listed with their numbers on the credentials page; design and construction under one contract is design-build.

Every deliverable below is produced in-house by our design team and reviewed by a registered Arizona professional engineer where the jurisdiction or the specification requires a seal. The list is long because a commercial electrical set is long; the point of each entry is to say what you get, what we need from you to produce it, and the Phoenix-specific rule that most often turns a set drawn to the national code book into a correction.

Load studies and demand calculations

The Article 220 calculation by panel and by feeder, with the mechanical load taken off the real equipment schedule rather than watts per square foot, and the connected and demand totals that set the service size, the transformer kVA and the number the utility application is built from. On an existing building, NEC 220.87 lets the existing load be established from measured demand — twelve months of utility data, or a 30-day recording — which is how a service upgrade gets sized honestly instead of from empty breaker spaces. Related: panel and service upgrades, transformer sizing calculator.

One-line diagrams

The one-line is a procurement document before it is a drawing. Service size, voltage, bus ampacity and interrupting rating all fall out of it, and all four lock the day the switchgear is ordered. Every APS commercial meter enclosure is submitted to APS for approval before it is manufactured, showing bus bracing, ampacity, dimensions, voltage and phase; SRP service entrance shop drawings go to shopdraw@srpnet.com. Phoenix plans submitted under the Annual Facilities Program must carry the one-line, the load calculations and the fault current calculations together. Related: service and distribution.

Feeder and conductor sizing, and voltage drop

Conductors sized at the 75°C termination column under 110.14(C), with ambient correction from a Phoenix design condition of roughly 110°F dry bulb and the 33°C rooftop adder of NEC 310.15(B)(2) where a raceway sits in direct sun less than 7/8 inch above the roof — a rule that was not deleted in 2017 and is still misquoted. Conduit-fill adjustment, and voltage drop held to the 3 percent branch and 5 percent total recommendations on the long site runs that Valley lots produce. In Phoenix, Glendale and unincorporated Maricopa County a wire-type equipment grounding conductor rides in every raceway under the local amendment to 250.118(4), sized per 250.122 and counted in the fill. Tools we use ourselves: wire ampacity, voltage drop, conduit fill.

Panel schedules

Circuit by circuit, with phase balance, connected and demand totals and a directory that reflects what is actually on each circuit. In Phoenix the schedule is reviewed with the load study and the one-line through SHAPE PHX, and an inconsistent schedule is a correction. Phoenix and Glendale amend NM cable out of commercial buildings under 334.10, so the raceway and conductor count behind each circuit is part of the schedule, not an afterthought. Related: panel schedule generator.

Short-circuit and available fault current

Available fault current at the service and at every downstream board, from the utility's contribution through the transformer and the feeders. Interrupting rating is a price and a lead time, not a checkbox, and it is the number that decides whether the gear on the one-line can actually be bought on the schedule. Series ratings where they are listed and where the AHJ accepts them. This work is part of every design we produce. Related: power studies.

Protective device coordination and arc flash

Separate deliverables from the design, and where they are issued as engineering studies they are sealed by the PE we coordinate rather than published under a contractor's name. A coordination study sets the settings and the curves; an arc flash study produces the incident-energy results and the label set the electrical rooms carry. Tell us at bid time whether the specification calls for a study, a label set, or both, because they price differently. Related: power studies.

Photometrics and outdoor lighting compliance

A point-by-point illuminance model built from the manufacturer's IES files for the exact fixture and optic, at the real mounting height and tilt, with a light loss factor that reflects dust and lumen depreciation rather than a factory-fresh number. Average, minimum and uniformity across the paved area, and the values at the property lines, which is what a zoning reviewer checks first. Outdoor lighting in the Valley is a zoning matter governed city by city — Maricopa County's outdoor light control provisions in Zoning Ordinance Chapter 11, Section 1112 work on shielding and lamp type — so the package flags the local rule it has to satisfy. Related: parking lot and site lighting.

Lighting controls and the energy code

Controls scope is a jurisdiction question. Phoenix deleted three sections of the 2024 IECC outright — C405.12 automatic receptacle control, C405.13 energy monitoring and C405.15, which would have required on-site renewables — and other Valley cities did not follow. A controls design that is right for Phoenix can be short of the requirement three miles away. We design to the adopted edition and the amendments of the city the permit is pulled in. Related: LED lighting retrofits.

Utility application packages for APS and SRP

To open a commercial new-service file APS wants the official street address and legal description, the structure type and square footage, the estimated load, the voltage and phase, and a site plan showing the desired meter location; the utility then engineers its system to your meter from that package. We open it the same week design starts, because neither APS nor SRP publishes a committed lead time and every week the file sits unopened is a week added to the end of the job. The two utilities are genuinely different — APS on an ACC tariff with a codified feasibility test and a five-year refund window, SRP self-governed with a contribution that is generally non-refundable — and the 200-amp threshold matters on both: APS requires EUSERC-approved CT-rated metering above 200 A, and SRP's 400 A Class 320 socket is residential-only, so commercial above 200 A is CT-rated there too. APS also caps a non-residential single-phase 120/240 V service entrance at 800 A. Related: service and distribution.

Permit sets and plan review response

A complete set for the jurisdiction the permit is pulled in — and the Valley is a dozen jurisdictions on three code cycles. Phoenix commercial review runs through SHAPE PHX, which took on commercial work on 27 April 2026; in its July 2026 report major projects averaged 30 calendar days for first review, medium 33 and minor 33 against a 25-day goal, so small tenant improvements are currently the slowest tier. We answer corrections as a single comprehensive response, which is what A.R.S. §9-835 limits a city to asking for in the first place. Related: service area for each city's adopted edition.

EV charging infrastructure

The 2024 Phoenix Building Construction Code adds EV-capable, EV-ready or EVSE requirements for new one- and two-family dwellings and townhouses — residential-scoped, and worth stating precisely because it is misquoted constantly. On townhouses Phoenix also added NEC 215.25: a feeder in one unit may only serve loads within that unit, so a shared house panel feeding chargers down a row does not work here; unit metering or a separately metered common-area service does. On commercial sites the design question is load management against the service the utility will actually give you. Related: commercial EV charging.

Design-assist and existing-building evaluation

When a design consultant is already under contract and the electrical sheets are nearly done, we come in as design-assist for the last engineering cycle: constructability, lead times and price against the set as drawn. On an existing building we start from the panel schedule, a photograph of the panel interior with the dead front off, and enough billing history to run the 220.87 measurement, and we tell you whether the service is genuinely short or only looks short on paper. Related: design-build, tenant improvement electrical.

A schedule that passes in San Diego can fail here on ampacity alone. ASHRAE's cooling design condition for Phoenix is roughly 110°F dry bulb, and the informational note under NEC 310.15(B) points at the ASHRAE Handbook as the source for site ambient — so 110°F is defensible rather than folklore. Table 310.16 assumes 30°C (86°F): at 41–45°C a 90°C conductor keeps 87 percent of its table ampacity, and at 46–50°C it keeps 82. The wire ampacity calculator shows what that does to a feeder.

Rooftop is worse, and the rule gets misquoted constantly. It was not deleted in 2017. NEC 310.15(B)(2) in the 2020 and 2023 editions still adds 33°C (60°F) where a raceway or cable sits in direct sunlight less than 7/8 inch above the roof — with an exception worth real money, since Type XHHW-2 is not subject to it. NEC 310.10(D) separately requires conductors in direct sun to be sunlight resistant.

• A wire-type equipment grounding conductor is required in Phoenix, unincorporated Maricopa County and Glendale, all three amending NEC 250.118(4) so EMT alone does not qualify. This is the fastest way an out-of-state design earns a correction notice.
• NM cable is amended out of commercial buildings in Phoenix and Glendale, which strike the Type III, IV and V language from NEC 334.10.

Open the utility file first, not last. Neither utility publishes a committed lead time for commercial new service — APS says only that timelines vary with complexity and current turnaround — so the only schedule protection available is starting early.

• The utility engineers its system to your meter panel, reviews the service entrance drawings, stakes and inspects trench, conduit and pads, sets the transformer and energizes. APS ESRM 200.1 lists the eight items needed to open the file.
• We obtain the permits, cut the trench to the utility's design, install conduit, pour the transformer pad and set the service entrance section. On an SRP job the pad, ground rod, conduit and backfill are customer-furnished.
• Nobody else energizes anything. Only authorized APS employees may energize an APS service, and SRP will not energize the load side until the AHJ has approved the installation.

Two hundred amps is the number to remember on both systems. APS requires EUSERC-approved CT-rated meter enclosures on every commercial service above 200 A, with test block or bypass provisions at 200 A and below (ESRM 302.9). SRP's accepted meter socket ratings are 100 A, 200 A and 400 A Class 320, and the 400 A socket is residential only — so commercial above 200 A is CT-rated there too. Working clearances belong on the site plan early, not after the civil drawings are approved.

Both standards move. SRP republished its Electric Service Specifications on 30 April 2026 and logged six further changes by 11 August 2026, one of which eliminated Customer-Owned Service after 6 July 2026. Its own sections disagree on the shop-drawing threshold — 225 amps in Section 1, 400 amps in Section 9 — so we submit at the lower number.

A load study can start from surprisingly little, but every item below removes an assumption from the set, and assumptions are what come back as corrections.

• The address and the jurisdiction — city or unincorporated county decides the code edition, the amendments and the review queue; the parcel decides APS or SRP.
• Site plan and floor plan, even preliminary, with the intended meter and gear locations if you have a preference.
• The mechanical equipment schedule — rooftop units, chillers, process equipment, with nameplate data. Mechanical is the load that most often gets guessed.
• Occupancy and use, and the tenant's process loads if it is a tenant improvement.
• For an existing building: the utility account, twelve months of bills, the existing panel schedules and a photograph of each panel interior with the dead front off.
• Specification sections if the job is plan-and-spec, so the set matches what the bidders will be held to.
• A target energization date, so the utility application and the gear lead time can be worked backward from it.
• Any owner-furnished equipment, because a meter enclosure the utility has not pre-approved is a schedule problem no design can fix.

1. Jurisdiction and utility confirmed. Adopted NEC edition and local amendments for the city, and APS or SRP established for the parcel rather than assumed.
2. Load study and one-line. Service size, voltage, bus ampacity and interrupting rating decided, because the gear order depends on all four.
3. Utility application opened — the same week, with the load and voltage from the one-line.
4. Feeders, panel schedules, photometrics and controls developed against the confirmed edition and amendments.
5. Sealed where required. The registered Arizona PE we coordinate reviews the set, revises what needs revising and seals what the jurisdiction or specification demands. We say which parts are ours and which are theirs before the contract is signed.
6. Submitted through SHAPE PHX or the relevant city portal, as one complete set.
7. One correction cycle, answered comprehensively.
8. Utility equipment approval before manufacture — the meter enclosure and service entrance section reviewed by APS or SRP.
9. Issued for construction, and record drawings at the end if we build it.