SIA 451 — Documentation of electrical installations in Switzerland

SIA 451: the Swiss standard for electrical installation documentation

The SIA 451 is published by the Swiss Society of Engineers and Architects (SIA, Zurich) in close collaboration with Electrosuisse and theEIT.swiss (Swiss association of electrical installers). Its scope covers the technical documentation of low-voltage electrical installations (≤ 1 000 V AC) in commercial, residential and light-industrial buildings, as well as public works (schools, hospitals, cantonal infrastructure).

The edition in force in Switzerland is the revised version published by the SIA in the « Building services » collection. It complements the NIBT 2020 (which governs the design and safety of the installation) and theOIBT (federal ordinance on low-voltage installations). Where the NIBT prescribes how to build, SIA 451 prescribes how to document.

The standard is built on three pillars: (1) the exhaustive list of deliverables expected at each project phase (preliminary design, design, execution, as-built), (2) the graphic conventions (symbols, layers, title blocks, formats), and (3) the archiving and updating rules of technical files. It is regularly cited in the CCT (technical specifications) of cantonal public tenders (VS, VD, GE, NE, FR, JU, bilingual BE) and in the framework contracts of large private building owners (property management companies, portfolio managers).

The SIA works in mixed technical committees including consulting engineers, installers, Swiss manufacturers and utility representatives (Groupe E, Romande Energie, SIG, Services Industriels lausannois). This shared governance guarantees a standard that is workable in the field and accepted by the entire building chain.

Why SIA 451 exists

Before SIA 451, every Swiss engineering firm delivered dossiers according to its own conventions: heterogeneous formats, symbols partially translated from French or German, incompatible cross-references between sheets, scattered legends. The result was a huge hidden cost at every change of contractor : an installer taking over a site left by a colleague had to mentally redraw half the dossier before continuing the work.

The standard therefore harmonizes the technical documents exchanged between the four major players of the Swiss chain:

• Engineering firms and consulting engineers who size installations and draft the calls for tenders;
• Electrical installers certified by Electrosuisse, who install and connect;
• Independent OIBT inspectors who inspect and issue the safety certificate (CSE) ;
• Local energy distributors who connect to the grid and archive the metering diagrams.

A SIA 451-compliant dossier considerably facilitates the OIBT final inspection : the inspector immediately finds the schematic diagram, the protective devices, the selectivity and the calculation notes. A non-compliant dossier extends the audit by several hours and bills the project owner accordingly.

Finally, the standard guarantees a durable archive over 20 to 30 years — typical service life of a building electrical installation. Documentary traceability is required by professional liability insurers and by judges in the event of a loss (fire of electrical origin, electrocution, business interruption). Several cantonal court rulings have held missing documentation to be an aggravating professional fault.

Mandatory documents according to SIA 451

A complete SIA 451-compliant dossier comprises nine main deliverables. Each can be demanded separately during an inspection, a transfer of ownership or a later conversion.

1. Block diagram (general single-line) — overview of the supply from the utility connection, metering and main overcurrent device down to the main distribution boards. A3 or A2 format depending on complexity. Shows cable cross-sections, upstream protection ratings, and any generator sets or UPS units.
2. Panel schematics (single-line sub-panels) — one sheet per sub-distribution board (T1, T2, kitchen sub-board, workshop sub-board, etc.). Details each outgoing circuit: protection (rating, curve, residual-current sensitivity), cable cross-section, length, designation of the downstream circuit.
3. Control schematics (multi-line if automation) — mandatory as soon as an automation goes beyond the simple two-way switch: scene-based lighting, BMS (building management system), contactors, latching relays, pump or ventilation control interlocks. Multi-wire representation with terminal and conductor identification.
4. Layout plans per floor — one plan per floor on an architectural background at 1:50 or 1:100 scale. Locates every device: luminaires, socket outlets, switches, detectors, sensors, multimedia connection points. Includes each device's circuit number.
5. Site plan / cable trays — for commercial and industrial buildings: vertical and horizontal cable tray routing, service shafts, fire-wall penetrations, outdoor pits.
6. Calculation note — written document or spreadsheet providing the cable sizing (current-carrying capacity, reference method per SN 411011/DIN VDE 0298-4), the cumulative voltage drop per circuit, the selectivity check between upstream and downstream protective devices, and the prospective short-circuit current calculation.
7. Legend of the symbols used — reference page listing all the graphic symbols used in the dossier, compliant with IEC 60617. Essential for a third party to understand the dossier without ambiguity.
8. Bill of installed material — exhaustive list of components (distribution boards, protective devices, luminaires, socket outlets, cables) with commercial designation, supplier, catalogue reference, quantity. Tabular format, ideally linked to the CAN catalogue for cost estimates.
9. Revision index, date and signatory — every document carries a standardized title block stating the revision index (A, B, C or 00, 01, 02), the date of that index, and the name and signature of the author or the office manager. Any subsequent modification increments the index and preserves the history.

Mandatory sections of a SIA 451 dossier

Graphic conventions

SIA 451 imposes precise graphical conventions to guarantee the readability and interoperability of project files. The preferred formats are A4 (calculation notes, schedules, reports) and A3 (panel schematics, block diagrams for small projects). Layout plans and site plans favour A2 or A1, at metric scale 1:50 or 1:100 to remain legible in print. Landscape orientation is the rule for schematics, portrait for text notes.

Each sheet bears a standardised title block placé en bas à droite. Il contient : le logo et la raison sociale du bureau d'études, le nom du maître d'ouvrage, le nom et l'adresse du projet, le titre du folio, le numéro de folio sur N total, l'échelle, le format papier, la date de création, l'indice de révision en cours, la date de cet indice, ainsi que les visas (auteur, vérificateur, approbateur). En cas de marché public, on ajoute le numéro de dossier cantonal.

The standard legend includes only the symbols actually present in the project, grouped by family: protective devices, control devices, socket outlets and connections, luminaires, automation, telecommunications, low-current systems. All graphic symbols must comply with IEC 60617 (2012 edition, multi-part series). The use of ANSI/IEEE 315 (Anglo-American) symbols is excluded for Swiss project files.

The trade layers AutoCAD or DWG are also standardised in Swiss practice. Engineering firms typically adopt the naming convention EB_* (ElectroBlocs): EB_PRO for protective devices, EB_LIG for lines and connections, EB_CON for contacts and controls, EB_TXT for texts, EB_CAR for the title block. This convention makes PDF export easier (freezing construction layers) and simplifies takeover by another office. See our complete guide on electrical trade layers.

SIA 451 vs SIA 144 vs SIA 380/4

Three SIA standards govern electrical installations in Switzerland, and they are frequently confused. Their scopes are nonetheless distinct and complementary:

• SIA 451 — Documentation. Defines the deliverables, their structure, their graphic conventions and their archiving. It is the standard for the technical file. It says nothing about calculation content or component selection.
• SIA 144 — Tendering and planning. Governs procurement procedures: tendering rules for engineering services, the design office's mandate, reference fees. It is the standard for the contractual process, ahead of the works.
• SIA 380/4 — Electrical energy in buildings. Sets the energy performance requirements for lighting and electrical installations: specific installed power (W/m²), luminaire efficacy, maintenance factor. It is the standard behind the energy calculation, complementary to EN 12464-1 (illuminance levels).

On a complete project, the three standards coexist: SIA 144 frames the engineering office's mission, SIA 380/4 sizes power and efficiency, SIA 451 codifies the delivered dossier. An installer complying with only one of the three produces a dossier that is incomplete from the cantonal point of view.

ElectroCAD tools for SIA 451 compliance

ElectroCAD is developed in Switzerland to natively produce SIA 451-compliant files, with no manual rework. The AutoCAD plugin ElectroSchema automatically generates single-line and multi-line diagrams with EN 81346 reference designations, automatic cross-page references, and material schedules auto-calculated as you draw. The symbols used come from the ElectroBlocs library (1187 validated IEC 60617 symbols).

The SIA title blocks are supplied as ready-to-use templates for each Swiss canton (VS, VD, GE, NE, FR, JU), with dynamic fields (project, client, revision index, date, signatory). Therevision index is incremented automatically at each major modification, and the history is kept in the DWG attributes.

The module ECPRESGEN enables thebatch PDF export of a complete document set in a single command: all sheets are assembled, paginated and delivered in SIA 451 format with automatic freezing of construction layers. Material lists are exported as .crbx (IfA18) directly usable by Swiss wholesalers and electrical quoting software.

An installer moving from bare AutoCAD input to ElectroCAD cuts SIA 451 dossier production time by a factor of 3 to 5, and eliminates the title-block, symbol and layer non-conformities that are the main causes of files being sent back to the engineering office.

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Automatic generation of compliant SIA 451 project files, Swiss title blocks included, batch PDF export and integrated CAN bill of quantities.

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