Guide

Bill of materials for an electrical installation: which items belong on it?

Seven item groups, how they derive from the single-line diagram and the position plan, the items that are routinely forgotten — earthing material, boxes, cable allowance, spare ways — and where the AREI fixes a quantity and where it does not.

Published on 31 August 2026 13 min

Which items belong on the bill of materials for an electrical installation?

Seven groups: distribution board, protective devices, cables, boxes, switches and sockets, earthing, small material. A list is not complete because all seven headings appear on it, but because every item has a traceable origin — a count from the plan, a rule from the AREI, or an explicitly stated assumption of your own business. Without that origin the quantity cannot be checked, and by the next revision of the plan it can no longer be corrected either.

Item group	Typical individual items	Quantity derives from	Regulatory anchor
Distribution board	Enclosure with back panel and door, rows and DIN rails, cover plates, busbars, end caps, feed terminals, labelling	Module count per row, separation by energy tariff	5.3.5.1 points a and c, 3.1.3.1
Protective devices	Main isolating switch, residual current devices 300 mA and 30 mA, circuit breakers, surge protective device where applicable	Number of final circuits and their allocation to the RCD groups	5.3.5.1 point b, 4.2.4.3 point b, 5.2.1.2
Cables	Cable per type, core count and cross-section in metres; conduit, pre-wired conduit, buried cable	Cable route per circuit plus allowance	3.1.2.2 point a, 5.2.1.2
Boxes	Junction and branch boxes, flush or hollow-wall device boxes, ceiling and wall outlet boxes, draw boxes	Number of devices plus number of branch points	3.1.2.2 point a, 5.2.6.1, 5.3.5.2 point a
Switches and sockets	Inserts, rockers and covers, frames per combination, damp-location variants with gasket	Number of control points and sockets from the position plan	3.1.2.3 point a, 5.3.5.2 points a and b
Earthing	Earth loop, earthing conductor, earth disconnecting link, main equipotential bonding conductor, supplementary bonding conductors, terminals	Building perimeter, number of extraneous conductive parts, bathrooms	5.4.2.1, 5.4.2.2, 5.4.3.5, 5.4.4.1, 5.4.4.2
Small material	Fixings and clips, terminals, strain reliefs, box lids, labelling material, gaskets	Ratio per item — company convention	5.2.9.5, 5.2.6.2 point b, 3.1.3.1

The last row is marked differently on purpose: for small material the AREI states no quantities. It states conditions from which the items follow — more on that below.

This article contains no prices. Not out of caution, but because a price range without a named source and date is wrong within a quarter and gets quoted onward regardless. For the cost side see How much does an electrical plan cost? and Cost comparison: drawing it yourself versus hiring an electrician.

Is a bill of materials required by the AREI?

No. The AREI knows the material list only as a permitted annex to the file: schematics, plans and documents "may be supplemented by documents describing the various characteristics of the electrical equipment and/or products in more detail" (sub-section 3.1.2.1 point c). The verb is may, not shall.

Mandatory for a new domestic installation are the single-line diagram and the position plan, drawn up by the person responsible for carrying out the work (sub-section 3.1.2.1 point a). If you attach the material list as an annex, it shares the regime of annexes: it is kept up to date and held on site at the disposal of anyone authorised to supervise, inspect, maintain, repair or modify the installation (sub-section 3.1.2.1 point d).

Practical consequence: the material list is a tool for costing and procurement, not an inspection document. The inspector does not flag its absence. What they do flag is material in the installation that does not belong there — and that is exactly what a clean list prevents, because it fixes the selection up front.

Which data must the plan carry for the quantities to be right?

The single-line diagram supplies almost the entire item list, but not the most important quantity. Sub-section 3.1.2.2 point a requires at minimum: type, cross-section and number of conductors of every cable, the installation method, type and characteristics of the residual current protective devices, type and characteristics of the overcurrent protective devices, the switches, the junction boxes, the branch boxes, the socket outlets, the lighting points, the fixed machines and appliances, and the sources.

That is a remarkably complete enumeration — and it contains no length. The length of the cables is required only for non-domestic installations (sub-section 3.1.2.2 point b). In housing, therefore, the decisive input for the cable quantity appears in no mandatory document at all.

Quantity on the list	Input value	In a mandatory document?
Number of sockets	Socket outlets on the diagram and the position plan	yes (3.1.2.2 a, 3.1.2.3 a)
Number of switches	Switches on the diagram, their location on the plan	yes (3.1.2.2 a, 3.1.2.3 a)
Number of boxes	Junction and branch boxes on the diagram	yes (3.1.2.2 a)
Number of circuit breakers	Number of final circuits	yes (3.1.2.2 a)
Cable type and cross-section	Type, cross-section, core count per cable	yes (3.1.2.2 a)
Cable length in metres	Route along walls, installation zones and storeys	no — only for non-domestic installations
Earthing material	Building perimeter, number of extraneous conductive parts	no — follows from chapter 5.4, not from the diagram
Small material	Installation method, fixing spacing, connection method	no — company convention

The position plan carries the location of that same equipment, not its count or its length (sub-section 3.1.2.3 point a). The cable quantity only emerges once a route has been drawn; the method is set out in Cable routes and cable lengths.

How many protective devices do I need — and where does the number come from?

Not from experience, but from four rules that jointly fix the module count in the board. This is the part of the bill of materials that the AREI drives most directly.

Rule	Reference	Effect on quantity
Main board fitted with a main isolating switch; in domestic installations not below 40 A	5.3.5.1 point b	1 item, rated current not below 40 A
At the origin of the installation at least one RCD of at most 300 mA, providing isolation	4.2.4.3 point b	at least 1 item at 300 mA
Immediately downstream at least one high or very high sensitivity device, to which sockets, lighting, the bathroom, washing machine, tumble dryer and dishwasher are connected	4.2.4.3 point b	at least 1 item at 30 mA
At most eight final circuits per such RCD	4.2.4.3 point b	from the ninth affected circuit onward, a further 30 mA device
At most eight socket outlets per final circuit	5.3.5.2 point b	from the ninth socket onward, another circuit with breaker and cable
At least two separate lighting circuits in dwellings with more than two rooms or areas	5.3.5.2 point b	minimum 2 lighting circuits
A separate circuit per appliance rated 2600 W or more, and for washing machine, dishwasher, tumble dryer, electric cooker, hob and oven	5.2.1.2	1 circuit, 1 protective device and 1 cable per named appliance
RCDs in domestic installations at least type A; at the origin of the installation a rated current of at least 40 A	5.3.5.3 point a	rules out type AC and sets a floor on the frame size
Protective and control devices on different energy tariffs grouped on separate panels at least 10 cm apart, or in separate boards	5.3.5.1 point c	enlarges the enclosure or forces a second one

This chain explains why a bill of materials built from a room count is almost always too short: the number of sockets determines not only the socket items but, through the rule of eight, also the number of circuits, hence the number of breakers, the number of cables, and ultimately the size of the enclosure.

Which appliances need their own circuit is covered in Appliances that require a dedicated circuit; the board layout itself in Distribution board planning.

Which earthing material is routinely forgotten?

Most of it. Earthing appears on the single-line diagram as one symbol, but on the bill of materials as six to ten items with prescribed minimum cross-sections. Those cross-sections are figures from the regulation, not from a catalogue.

Item	Prescribed minimum	Reference
Foundation earth loop	at least 35 mm² geometric cross-section, solid conductor or seven stranded cores, without welds	5.4.2.1 points b.1.3 and b.1.2
Metal of the earth loop	bare annealed electrolytic copper or lead-sheathed copper	5.4.2.1 point b.1.4
Fixing of the earth loop	copper only, or materials that cause no corrosion	5.4.2.1 point b.1.5
Supplementary electrode, horizontally laid	at least 35 mm², buried at least 0.80 m deep, minimum length 15 m	5.4.2.1 point b.3
Supplementary electrode, rod or pin	minimum length 1.50 m, of which at least 1.50 m driven below the −0.60 m level	5.4.2.1 point b.4.1
Earthing conductor	16 mm² copper with corrosion-protective coating, otherwise 25 mm² copper, 50 mm² for aluminium or steel	5.4.2.2
Earth disconnecting link	a disconnecting device removable only with a tool	5.4.3.5
Main equipotential bonding conductor	half the cross-section of the largest protective conductor, minimum 6 mm² copper, may be capped at 25 mm²	5.4.4.1 point a
Supplementary bonding conductors	at least 2.5 mm² if mechanically protected, 4 mm² if not	5.4.4.2 point a

Three points that go missing in estimates:

The earth loop is site material, not electrical material. It is required for every new building whose foundation trench bottom reaches at least 60 cm (5.4.2.1 point b.1.1), and it is laid long before anyone thinks about sockets. Drawing up the electrical bill of materials after the shell is complete structurally puts this item out of view.
The ends remain accessible for inspection (5.4.2.1 point b.1.6). That is an execution requirement with a material consequence: pit, cover, marking.
Main equipotential bonding is not a single terminal, but one conductor per extraneous conductive part — water, gas, heating — with a clamp on the pipe concerned. The quantity follows from the building services, not from the electrical plan.

Which earthing system applies is covered in Earthing TT or TN-S.

Why are junction boxes and device boxes so often missing from the list?

Because mentally they belong to the cable and in the catalogue to the accessories — whereas the AREI names them explicitly as elements in their own right.

Four rules make them unavoidable:

Connections may only be made in specific places: in distribution and switchgear assemblies, in junction or branch boxes, at the terminals of switches or socket outlets, or in sufficiently large ceiling boxes from which luminaires are suspended (sub-section 5.2.6.1). Every branch on the plan is therefore a material item.
Connections inside conduit are prohibited (sub-section 5.2.9.3 point f). A route drawn without a box is a non-compliant execution.
In junction, branch and draw boxes the conductors remain accessible; tees and elbows are prohibited (sub-section 5.2.9.3 point i.2). This rules out the smallest possible box and feeds through to the frame size, hence the price.
Socket outlets built into walls are housed in metal boxes or in boxes of insulating material (sub-section 5.3.5.2 point a). The device box is therefore not optional but mandatory material — one per flush point, and a different type in a hollow wall than in masonry.

On top of that, junction and branch boxes are part of the mandatory content of the single-line diagram (sub-section 3.1.2.2 point a). A diagram without them is incomplete — and so is a bill of materials derived from such a diagram.

How much cable allowance should I include?

On the size of an allowance the AREI says nothing — no percentage, no reserve length, no waste factor. Any figure you use is a convention of your own business and belongs in the calculation sheet as such.

What the regulation does fix are the conditions from which an allowance follows:

Connections at appliances must not be subjected to tensile or torsional forces (sub-section 5.2.6.2 point b).
In vertical runs, tensile forces from the cable's own weight must not act on the connection terminals (sub-section 5.2.9.5).
In conduit it must be possible at all times to draw in or remove conductors or cables (sub-section 5.2.9.3 point e).
In boxes the conductors remain accessible (sub-section 5.2.9.3 point i.2), which does not work without a loop inside the enclosure.

The allowance is therefore not a safety cushion on an uncertain calculation, but a material item with a purpose. If you apply it as a flat percentage, document the percentage, its origin and the revision it applies to. Deriving the base length is covered in Cable routes and cable lengths; which accompanying material each installation method brings with it in Installation methods under the AREI.

How many spare ways belong in the distribution board?

The AREI prescribes no spare ways. A full-text sweep of the nine parts in the Dutch, French and German versions returns no passage naming a number of free modules, a percentage or a minimum reserve. Anyone quoting a figure is quoting a company convention — which is legitimate, as long as it is said that way.

What the regulation does require instead, and what points in practice in the same direction:

Circuits are arranged so that they can later be identified during supervision, inspection, maintenance, repair, modification or extension of the installation (sub-section 3.1.3.1).
Control, protective and isolating devices are individually marked clearly, conspicuously and indelibly (sub-section 3.1.3.1). Labelling material is therefore an item, not a courtesy.
Circuits connected upstream of the board's main switch must be identified as such (sub-section 3.1.3.1).
Every modification or extension is shown on the position plan, which reflects the existing state at any moment (sub-section 3.1.2.1 point a).
Equipment in the board remains easily accessible, in domestic installations without special means (sub-section 5.3.5.1 point c).

And one enclosure rule that is overlooked more often than spare ways: in domestic installations, distribution and switchgear assemblies are class I or II, with a back panel and a door, made of non-combustible and non-hygroscopic material; the back panel must remain non-removable for the entire service life of the equipment (sub-section 5.3.5.1 point a). Door and back panel are therefore not an equipment option.

Where is the boundary between material cost and labour cost?

At the question of whether the quantity follows from the plan or from the execution.

Material cost follows from piece counts and metres and can be derived from the model. Labour cost follows from routes, substrates, accessibility and sequencing — quantities that appear neither on the single-line diagram nor on the position plan. The same socket costs the same material whether it goes into a hollow wall or into concrete; the effort differs by a wide margin.

In practice, for estimating:

A bill of materials is not half a quotation. It is the half that can be checked.
Items that touch both — chases, penetrations, core drilling, scaffolding — belong explicitly on the labour side, otherwise they appear nowhere.
The installation method decides both sides at once: it determines which accompanying material is needed and how labour-intensive the execution becomes.

Figures for both sides are in How much does an electrical plan cost? and Cost comparison: yourself or an electrician. This article deliberately does not repeat them: prices age, the method does not.

Which estimating mistakes make the list unusable?

Counted per room instead of per circuit. The rules of eight — sockets per circuit and final circuits per RCD (5.3.5.2 point b, 4.2.4.3 point b) — generate items that appear in no room-by-room list.
Straight-line distance instead of cable route. Indoors the straight line sits systematically well below the real route; it is not an estimate but a lower bound.
Net lengths used without an allowance. The allowance exists for the four reasons above, not out of caution.
Earthing material forgotten, because it is one symbol on the diagram and a shell-construction topic on the schedule.
Device boxes and branch boxes treated as accessories, although they are mandatory diagram content (3.1.2.2 point a) and compulsory in masonry (5.3.5.2 point a).
Frames and covers not listed separately. A triple combination is one frame and three inserts, not three complete devices.
A circuit with no drawn cable drops out silently and makes the total length too small without any line being missing.
Prices carried over from an older revision without noting date and source. A quantity without a price is incomplete; a price without a date is wrong.

How is the bill of materials produced in PlanElec — and what does it not say?

Through the Export tab. The Material List appears there as a separate document; the Open material overview button shows it in detail, and the PDF comes from the same derivation.

What the overview contains:

Items in seven categories: Consumers, Equipment and inserts, Covers and frames, Installation material, Protection devices, Cables, Distribution.
Two views: By category and By room; items with no room allocation appear separately so they do not vanish quietly.
A header showing the number of consumers, positions, parts and the cable length.

Since the update of 16 July 2026 the overview breaks sockets, switches and selected connections down into manufacturer-neutral individual parts — inserts, covers, frames and installation boxes. Fixed appliances include a connection box, terminal and strain relief; appliance-specific accessories are not included. Enclosures and busbars follow the modelled row and module count.

Six base assumptions are shown explicitly in the overview rather than acting in the background. The one that matters most for estimating: cable lengths are net lengths from the model; waste and installation allowances are not included. The allowance from the section above is therefore not yet in there. Equally explicit: the device box follows an unambiguously linked wall; otherwise hollow-wall boxes are assumed for rooms containing hollow walls, and flush boxes elsewhere.

What the list deliberately does not do:

It quotes no prices and is not an order release. All items are manufacturer-neutral and must be resolved to concrete articles and professionally verified before ordering.
It invents no missing quantities. A circuit without a cable route appears at 0 m with the note "Routing missing" rather than being estimated. A suspiciously lean list usually contains exactly those lines.
It adds no earthing material that is not in the model. Earth loop, earthing conductor and bonding conductors are model content, not an automatic addition.
For PV installations, open DC material data are reported as notices — missing strings, module types or route lengths — instead of being papered over.

What the AREI self-check does not do here

The self-check assesses the planned installation, not the completeness of a bill of materials. Specifically:

It checks no quantities. There is no rule that reports a missing, under-dimensioned or duplicated item.
For earthing it checks only whether main equipotential bonding and the earth electrode are documented and whether the earthing system fits — not the cross-section of the installed conductor or the metres of earth loop required.
It checks no prices, no availability and no article allocation. Manufacturer-neutral items stay manufacturer-neutral.
It calculates voltage drop only when the path is complete; if a partial length is missing it reports a data gap instead of a result. For the bill of materials that means the cable quantity can be incomplete without any rule firing.
It replaces neither measurement nor inspection. The official assessment is made exclusively by a recognised inspection body.