Why the electrical room can cap the project
On a large commercial building the roof area is rarely the limiting factor. A distribution center may have more roof than any sensible array needs, while its main switchboard is full, its bus is rated tightly against its main breaker, and its transformer is owned and controlled by the utility. In that case the system is limited by the point of interconnection, not the number of modules that fit. A survey that records the roof carefully but treats the electrical room as a few photographs delivers half a record.
Start at the utility meter and work inward
The most reliable way to capture an electrical service is to follow the power. Begin at the utility transformer, then the service conductors, the meter and current transformer cabinet, the main service disconnect, the main switchboard or switchgear, and finally the distribution panels that the building actually uses. At each stop, record what it is, who owns it, and what it is rated for.
- Transformer. Pad-mount, vault or pole-mounted, the nameplate kVA and impedance where visible, and the owner. A utility transformer is the utility's equipment and cannot be altered by the project.
- Service voltage and configuration. Commonly 208Y/120 V or 480Y/277 V three-phase on commercial buildings. Record the actual configuration, including any high-leg delta service, which affects equipment choices.
- Meter and CT cabinet. Meter location, meter number, and whether the utility seals the cabinet. Many utilities do not allow anyone but their own staff to open it.
- Main service disconnect. Rating, manufacturer and model, plus the location relative to the meter.
- Switchboard or switchgear. Manufacturer, model, bus rating, main device rating, short-circuit rating and the arrangement of the sections.
- Available fault current. A label, an existing study or a utility letter. New equipment must have an adequate interrupting rating.
Load-side or supply-side: photograph both
A load-side connection lands the PV output on a breaker in the switchboard. It is limited by the busbar rules in NEC 705.12. A supply-side connection taps the service conductors between the meter and the main service disconnect under NEC 705.11 and is not subject to those busbar limits, but it needs physical room, a suitable tap method and utility acceptance. Which option works depends on details that only show up on site.
The survey should therefore capture the evidence for both. For a load-side option, photograph the bus labels, the available breaker spaces and the position of the main relative to any spare positions. For a supply-side option, photograph the service entrance area, the space around the meter and main, the conductor sizes visible, and any wall or ceiling that would constrain a tap. The engineer can then pick the best approach without sending the crew back.
Space, clearance and routing
Inverters, AC combiners, disconnects and sometimes a new transformer all need a home. The electrical code requires working clearances in front of equipment, so the available wall and floor space is smaller than it looks. Measure the proposed equipment location, the clear depth in front, headroom, and the path from the equipment to the point of interconnection.
Then record the conduit route from the array to the equipment. A commercial route may cross a roof edge, run down an exterior wall, pass through a mechanical room and cross a parking lot. Each leg needs a length, a penetration and an owner. Long runs change voltage drop and cost, so the engineer needs actual distances, not approximations from a satellite image.
Rapid shutdown and labeling constraints
Rapid shutdown under NEC 690.12 shapes the layout of conductors on and in buildings. Photograph where the array conductors would enter the building and where the rapid shutdown initiation device could sit. Also capture existing labels and any existing PV or generation equipment, because adding to an existing system brings additional rules.
What to ask the building owner
- The electrical single-line diagram and any recent power studies.
- Whether the service has been upgraded or expanded since the original drawings.
- The utility account details and rate schedule, plus interval data if the utility provides it.
- Planned loads such as EV charging, new equipment or an expansion, which change the right interconnection choice.
- Shutdown windows, because a supply-side tap or switchgear change usually requires an outage.
Questions that change the interconnection plan
Several facts discovered during the electrical walk can change the whole plan, so it is worth asking about them deliberately. Is there an existing generator, battery or PV system on the service? Existing generation changes the busbar calculation and the labeling. Is the building served by more than one meter or service? A campus with several services may allow the system to be split. Is a service upgrade already planned? If so, the solar design may be able to piggyback on it instead of working around the old gear.
Also ask how the utility treats commercial interconnections in that territory. Application timelines, study requirements and technical standards differ between utilities, and the survey is a convenient moment to collect the interconnection contact and any published guidelines. The survey crew does not decide those questions, but a record that lists the utility, the account and the contact lets the engineer start the application promptly.
Finally, note the physical condition of the equipment. Corrosion, heat discoloration, loose or missing covers and outdated gear are worth flagging to the owner, because the engineer may recommend replacing equipment instead of connecting new generation to it.
Handing it to engineering
Electrical engineers read the record in a particular order: service and ratings first, then space, then routing. Organize the deliverable the same way, with legible nameplates, labeled photos and a short note calling out anything unusual. Our companion note on main switchgear photos and documentation goes into what a legible nameplate set looks like, and the survey-to-plan-set handoff note covers how the record becomes drawings.
Solar Survey AI captures the electrical room as part of a commercial on-site survey, alongside the roof and structure in one visit, with the deliverable 48 hours after the survey. C&I design and engineering then works from that record and is PE stamped. If you are scoping a project and are unsure whether the electrical service can support the system you have in mind, the electrical zone is the first place to look.