Single-Line Diagram vs. Situation Plan: Difference and Coordination

The difference in one sentence

The single-line diagram shows how supply, protective devices, cables and loads are connected electrically; the situation plan, called a position plan in the regulation, shows where that equipment is located in the building. The same circuit letter and sequence number link the electrical path to the real room.

For a new domestic installation and for substantial modifications or extensions, you need both documents (AREI/RGIE Book 1 V06, Subsection 3.1.2.1 a). They do not replace each other: a floor plan does not specify RCDs, breakers or conductor data, and an electrical tree does not locate the socket beside a particular door.

Both documents at a glance

A shared identity and revision

Section 3.1.2 requires an unambiguous number, revision and revision date on all diagrams, plans and records. Domestic diagrams and plans also state the name, capacity and, where applicable, VAT number of the person responsible for the work, plus the installation address (3.1.2.1 a). Voltage and type of current appear on the single-line diagram.

When the approved body establishes conformity at the inspection, it dates and signs the diagram and plan together with the responsible person; with the inspection report, they become part of the installation file. A PDF you export before the inspection is therefore your well-prepared draft; it becomes approved through the approved body's endorsement.

What the single-line diagram contains

Subsection 3.1.2.2 a lists at least:

• cable type, cross-section and number of conductors;
• installation method of the cables;
• type and characteristics of residual-current devices;
• type and characteristics of overcurrent devices;
• switches, junction boxes and branch boxes;
• socket outlets and lighting points;
• fixed machines and appliances;
• sources such as transformer, solar cell, inverter or battery.

It answers structural questions: which RCD is upstream of circuit C, which breaker protects the cable, how many conductors of which cross-section run to the branch box, and which loads follow? Whether the box sits left or right of the door is not shown.

Each elementary circuit receives a capital letter. Lighting points, socket outlets and control units are numbered in order from the upstream overcurrent device. That sequence is an electrical reference, not a walking route through the rooms.

What the situation plan contains

Subsection 3.1.2.3 a requires the location of the items shown on the single-line diagram:

• distribution and switchgear boards;
• junction and branch boxes;
• socket outlets, lighting points and switches;
• fixed machines and appliances;
• sources such as solar cell, inverter, battery or transformer.

The basis is a legible floor plan that distinguishes storeys and rooms. Chapter 2.12 defines a plan as a to-scale representation of where the parts of the installation are; AREI/RGIE does not prescribe a specific ratio such as 1:50. What counts is an unambiguous position: if a socket sits on one wall or worktop, you draw it there and not somewhere in the middle of the room. Concealed junction boxes matter in particular, because later work must be able to find them.

The situation plan is not a complete cable-route plan. Subsection 3.1.2.3 a calls for the locations of the listed items; you do not invent unknown routes. For the location of underground cables, Book 1 sets its own duties (Section 9.1.5).

The shared reference is the bridge

Suppose circuit B supplies three socket outlets and one lighting point. The single-line diagram identifies them B1 to B4 in electrical sequence. The situation plan places each reference at its real location. A switch controlling B4 carries the letter B and the number 4 of the controlled point (3.1.2.1 a).

Inspector and electrician can then move from the protective device to the load and from the room back to the board. If B3 is missing from the floor plan, its location is unknown. If the plan shows a further socket B5 that does not exist on the single-line diagram, the two documents describe different installation states.

Build both from one survey

Drawing the diagram first and the floor plan weeks later from memory creates contradictions. Produce both from the same survey:

1. record storeys, rooms, boards and sources;
2. record the protective chain and final circuits in the board;
3. assign every socket, appliance and box to the correct circuit;
4. create each reference once and reuse it in both views;
5. add cable and equipment properties to the electrical path;
6. verify positions on site;
7. export both documents with the same revision and status date.

A board label helps with assignment but does not prove it. In an existing installation, you identify circuits competently and with the supply isolated. A guessed concealed connection does not belong on the plans as an established fact.

Alterations and document history

For a non-substantial alteration, a short description with the name, capacity and address of the responsible person, dated and signed, is enough instead of a new single-line diagram. You update the situation plan with every alteration or extension so that it always shows the existing layout. A substantial modification or extension, for example adding a circuit to a domestic installation (an example given in Chapter 2.11), requires new or updated diagrams and plans.

Parts whose on-site installation began before 1 October 1981 and which appear on the single-line diagram are marked as an "older part". The label places the existing work; it is neither proof of conformity nor an exemption. The derogations for old installations are assessed separately.

Manage both documents as a pair. A situation plan at revision 4 beside a single-line diagram at revision 2 leaves unclear what belongs together. Keep earlier endorsed revisions in the file rather than erasing the history.

Typical inconsistencies

How the inspection uses both

In the conformity inspection report for a domestic installation, the approved body certifies among other things that the installation was carried out in accordance with the single-line diagrams and situation plans (Subsection 6.4.6.4). The plans therefore have to be right, not merely present. The single-line diagram makes protection and wiring assignments traceable; the situation plan leads to the identified points on site. Visual inspection, tests and measurements complement the document check.

A mutually consistent pair can still contain a technical fault, such as an undersized cross-section. Conversely, technically sound work is poorly documented when the plans contradict each other. Keep three stages separate: the records are complete, the design has been competently checked, and the installed system has been officially inspected. Each stage has its own evidence.

After the inspection, the owner receives the endorsed plans and report for the file; the approved body keeps a copy for five years (3.1.2.1 a). The owner still keeps their own file current and makes it available for later work (9.1.2).

Treat the approved body's copy as a safety net, not version control. A later alteration kept only on a loose sheet makes the set inconsistent again. Attach each change to the correct revision of both documents.

A practical reconciliation before release

Do not just compare two pages side by side; work circuit by circuit. First write down the list of circuit letters. Then follow each circuit from its protective device to the last item and ask both documents the same questions: which points exist, which reference do they carry, where are they located, and what fixed function do they have? Record a mismatch as an open task instead of hiding it under a vague room label.

For circuit H, the list might contain ceiling light H1, wall light H2 and their switches. The single-line diagram shows how these points sit electrically behind protection and cable; the situation plan shows H1 in the hall and H2 outdoors. If H2 is missing from one sheet, the other is not automatically correct: survey and installed work decide, then you correct both documents.

Also run cross-circuit checks:

• Every board and fixed source on the single-line diagram has a findable location.
• Every relevant junction and branch box uses the same identifier throughout.
• Fixed machines are not represented only by room text on the floor plan.
• Continuation references between sheets end at the intended circuit, not at a similarly named group.
• Header, address, page numbering, date and revision visibly form one set.

Example: recording a small extension

When a socket is added in a study, first establish which circuit it is actually connected to. If it is the next point on circuit D, it becomes, for example, D6; you add that code at its electrical position on the single-line diagram and at its physical position on the situation plan. You do not infer cable and protection from the neighbouring socket; you verify them at the real connection. Advance the date and revision of both sheets together.

Whether work is substantial or not is a professional judgement. The short description is not a catch-all for years of small changes kept outside the plans. As soon as assignment or current state is no longer clear, you consolidate the documents into a new revision.

The official FPS Economy page on domestic electrical inspections summarises the content and relationship of the two documents. The current Book 1 remains decisive; the examples there are guidance and do not replace a survey of your installation.

What PlanElec handles

PlanElec brings floor-plan positions and electrical topology together in one project. Every device exists once: as soon as you assign it to a circuit, single-line diagram and situation plan carry the same reference. You export both as PDF from the same saved project state, and the advisory AREI/RGIE self-check shows you errors in the supported rules that can be decided from your data.

The roles are clear: PlanElec keeps plan and diagram consistent; the on-site survey, measured values and confirmation of concealed cables come from the professional. The endorsement of the plans and the official inspection report come from the approved body.

Related guidance

• What is a situation plan?
• AREI symbols for both diagrams
• New-build single-line diagram checklist
• Draw a situation plan step by step

Open PlanElec to prepare and export both diagrams →

Basis: AREI/RGIE Book 1 V06, Chapter 2.12, Section 3.1.2, Subsection 6.4.6.4 and Section 9.1.2. Editorial review: PlanElec team, 5 October 2026.