What a BTI plan gives you
A BTI plan is a measured drawing of existing premises, produced for inventory and registration. It is authoritative about walls and areas and almost silent about everything electrical.
| Content | Usually present | Useful for electrical design |
|---|---|---|
| Wall positions and thicknesses | Yes | Room boundaries, route planning |
| Room names and areas | Yes | Load assumptions, device counts |
| Door and window openings | Usually | Device placement, switching logic |
| Dimensions and scale | Often partial | Calibration, checking traced geometry |
| Existing electrical points | Rarely, and usually not current | Reference only — verify on site |
| Structural detail (beam depths, shafts) | No | Route conflicts, drilling restrictions |
| Heights, sections, elevations | No | Mounting heights, riser design |
The last three rows explain why an import is a starting point: the drawing says where the walls are, not where you may drill or how thick the slab is.
Step 1: read the plan before importing it
Two minutes here saves twenty later.
- Check the date and revision. Renovation plans are often older than the alterations already built.
- Find the scale. Look for 1:100, 1:200 or a scale bar. If both are missing, calibrate from a known dimension.
- Check orientation and mirroring. Scans get flipped. Compare window positions with a photograph of the facade.
- Note what is missing. Merged rooms, loggias counted as living area, single-line walls — all of it changes the design.
If the plan is a photograph of a printout, straighten and crop first. A 3° skew is invisible to the eye but displaces the far end of a 10 m room by about 0.5 m (10 m × tan 3°), which is enough to put a traced wall on the wrong side of a partition while the drawing still looks right.
Step 2: calibrate the scale
This is the step people skip, and the one that ruins the project quietly. Everything downstream — cable lengths, voltage drop, bill of materials — inherits the scale error.
Pick two points with a known distance, enter the real value, and verify on a second dimension. If the second check lands within about 1%, the calibration is good. If it lands at 4%, you picked the wrong reference or the scan is not uniformly scaled.
Common sources, in order of reliability: a dimension printed on the plan, the stated room area, a measured wall, the facade dimension.
Do not calibrate from furniture. Furniture is drawn to look right, not to be measured.
Step 3: trace walls and rooms
Recognition handles the bulk of it. Vector PDFs — exported from CAD rather than scanned — come through almost cleanly, because the lines are real geometry with coordinates. Scans need more help: contrast, deskew, then a pass to merge broken segments.
What to check after recognition:
- Room count. Count them against the plan. A missed room is invisible in the model and obvious in the design.
- Closed contours. An open contour does not become a room, so its area is zero and its lighting calculation is meaningless.
- Wall thickness. Thin interior partitions and structural walls behave differently for routing and for drilling.
- Door swings. They decide where a switch goes and which side of a wall a socket belongs on.
Where recognition fails, trace manually. It is still faster than starting from an empty canvas, and the result is a model you can dimension, not a picture.
Step 4: place points and group circuits
Now the design work starts. Place sockets, switches, luminaires and equipment against the plan, then group them into circuits.
Rules of thumb that survive contact with reality:
- Group by room and function, not by convenience. One circuit per room is a starting point; kitchen and bathroom get their own protection regardless.
- Keep wet areas on dedicated residual-current protection. Socket outlets in bathrooms and near sinks are the classic finding in a design review.
- Count the load before you count the points. Twenty sockets on one 16 A circuit is a plan for a tripped breaker.
- Leave spares in the panel. Ten to twenty percent spare ways is cheaper than a second panel later.
If the existing panel is reused, record its ratings and free ways as you go — retrofitting a schedule from photographs is slower and less accurate.
Step 5: panel, single-line diagram, calculations
With circuits defined, the rest is derivation rather than drawing.The panel schedule fills from the circuit list: breaker ratings, cable sizes, loads, spare ways. The single-line diagram builds from the same data, so the outgoing ways on the diagram match the schedule by construction rather than by proofreading. Calculations follow: load per circuit and panel, voltage drop over the traced route, conductor sizing against the protective device.
This is where a plan-based tool separates itself from a drawing tool. When schedule and diagram read from one model, "the plan shows 14 groups, the schedule has 12" cannot occur. To see that chain end to end, run a small flat through the demo.
For the numbers behind the checks, the load calculation and voltage drop guides walk through the methods.
Step 6: documents and export
The deliverable is rarely a single file. A typical package:
- Floor plan with devices, circuits and legends (PDF, and DXF if the contractor uses CAD)
- Single-line diagram (PDF)
- Panel schedule (PDF, XLSX for the electrician on site)
- Cable and materials specification, ready for pricing
Export early and often. A plan that looks right on screen can produce a DXF with exploded text or a PDF with unreadable line weights at A3. Check one sheet at print scale before sending. Export formats and limits are in the documentation; project limits are on pricing.
Quality checklist before you send it
| Check | Why it matters |
|---|---|
| Scale verified on two dimensions | Every length and load depends on it |
| Room count matches the source plan | A missing room is a missing circuit |
| Every room has lighting and switching | The most common omission in fast drafts |
| Wet areas have dedicated RCD/GFCI protection | Safety and the first thing a reviewer looks for |
| Circuit loads within breaker ratings | Prevents nuisance tripping and cable overload |
| Panel has spare ways and a labelled schedule | Installation and future maintenance |
| SLD, schedule and plan agree on circuit count | The classic three-document contradiction |
| Export checked at print scale | What you see is not always what prints |
Honest limits
- A BTI plan is not a survey. It records what was registered, not necessarily what was built. Verify openings, wall positions and heights on site.
- Recognition is not infallible. Skewed scans, handwriting, layered PDFs and low contrast degrade results. Budget a correction pass on every import.
- The plan has no electrical truth. Existing points, cable routes and panel locations must be verified physically.
- Constraints live outside the model. Load-bearing walls, risers, metering rules and landlord requirements are project-specific and often verbal. Write them down.
- The tool does not sign. Design responsibility stays with the qualified person who issues the drawing.
Fifteen minutes is realistic for the drafting chain: import, calibrate, trace, place, schedule, export. It is not realistic for the survey, the client conversation or the review — and those decide whether the design is right.
If you have a plan you already know well, that is the best test: import it, build the circuits, compare the result with the design you delivered. The demo needs no installation and no card.
Sources
- NFPA 70, National Electrical Code — device locations and protection requirements: nfpa.org/70
- IEC 60364 series, Low-voltage electrical installations: IEC Webstore
- Rosreestr — technical inventory and cadastral records in the Russian Federation: rosreestr.gov.ru
- Schneider Electric, Electrical Installation Guide: electrical-installation.org
Requirements for existing-building documentation vary by country. Confirm what your authority accepts before relying on an inventory plan as a design basis.
A measured plan of existing premises issued by a technical inventory bureau, used for registration and property records. It shows walls, rooms and areas; it rarely shows current electrical installations and usually arrives as a PDF or scan, not a CAD file.
You can trace it into vector geometry, which is what a CAD import does. The result is a drawing derived from the PDF, not a recovery of the original CAD file. Accuracy depends on scan quality and scale calibration.
On clean vector PDFs it needs only light correction. On skewed scans with handwriting and merged lines, expect to fix contours manually. Always compare the detected room count against the source plan.
No, but you need a calibrated plan and a site check. The DWG saves tracing time; it does not replace verification of what is installed.
The drafting chain — import to exported PDF — takes minutes on a typical apartment. Survey, client decisions and review are separate and dominate the calendar, not the software.
Yes, with more attention to diversity, three-phase balance and dedicated supplies for equipment. Import and tracing are identical; the engineering after them is not.
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