Guide

Electrical planning across several floors: does every storey need its own board?

When a sub-distribution board per floor earns its place, how to size and protect the riser, what the AREI/RGIE actually says about selectivity, and how storeys appear on the position plan and the single-line diagram — with the article reference beside every statement.

Published on 31 August 2026 14 min

Does every storey need its own board?

No. The AREI/RGIE knows no rule along the lines of "one board per floor". It requires a main distribution and switching board fitted with a general load-break switch whose rated current, in domestic installations, is not less than 40 A (sub-section 5.3.5.1 point b), and it requires distribution and switching boards in domestic installations to be easily accessible without special means (point c). Whether a second board upstairs belongs to that picture is your decision — not the standard's.

What the standard does impose are quantity limits, and those are exactly what drive the circuit count up in a three- or four-level terraced house: no more than eight single or multiple socket outlets per final circuit, and at least two separate lighting circuits for dwelling units comprising more than two rooms and/or locations (sub-section 5.3.5.2 point b), plus no more than eight final circuits per high-sensitivity residual current device (sub-section 4.2.4.3 point b). A sub-distribution board follows from those limits and from cable runs — not from a floor boundary.

The term the AREI/RGIE uses helps frame the thinking: an elementary circuit is the part of an installation between two successive overcurrent protective devices — as a main circuit or a sub-circuit — or downstream of the last such device, in which case it is a final circuit (section 2.6.1). The riser feeding a sub-distribution board is therefore not a final circuit but a main circuit. Every rule aimed at final circuits — the eight sockets, the eight circuits per RCD — does not apply to it.

When does a sub-board per floor make sense — and when not?

The decision reads off four observable quantities: the number of final circuits, the longest cable run, accessibility, and the extension you already know is coming. The table below summarises what actually turns up in a Belgian dwelling; the standard column names the provision that creates the limit in the first place.

Situation	One board is enough	Sub-board per floor justified	AREI/RGIE reference
Two levels, compact terraced house, under roughly 15 final circuits	✓	—	no prescription; the count follows from 5.3.5.2 b and 4.2.4.3 b
More than 16 final circuits, so more than two high-sensitivity RCDs	—	✓	at most 8 final circuits per high-sensitivity RCD (4.2.4.3 b)
Longest run well beyond 25–30 m from the board	—	✓	voltage drop to be limited according to the rules of good practice (section 5.2.5)
Attic with a heat pump, charge-point provision or a home office planned	—	✓	supply power to be determined with diversity factors (section 3.2.1)
Board in the cellar, upper floor reachable only by ladder	—	✓	easily accessible without special means (5.3.5.1 c)
Separate energy tariffs or a DSO meter of its own per level	—	✓	separate panels at least 10 cm apart, or separate boards (5.3.5.1 c)
A rental flat per floor, each with its own installation	—	✓	every dwelling unit is a domestic installation in its own right (3.1.2.1 a)
Renovation, one storey stays untouched for now	✓	—	the inspection is limited to the added or modified part (6.4.7.3)

Two arguments that regularly speak against a second board: every additional board is one more place that has to stay accessible, operable and maintainable without special means (5.3.5.1 c), and it has to carry an individual identification with the supply voltage clearly and conspicuously indicated (sub-section 3.1.3.3 point a). In a two-bedroom duplex that costs more than it saves in cable.

How do I size the riser to the sub-board?

In three steps, only the last of which carries a number in the AREI/RGIE.

First, the supply power. When determining the supply power of an installation or of part of one, diversity and utilisation factors of the loads may be taken into account (section 3.2.1). The regulation puts no figure on it — which factor is appropriate is a matter of the rules of good practice and of how the floor will actually be used.

Second, the current-carrying capacity. The current-carrying capacity I_Z of an electrical line depends on the conductor cross-section, the insulation, the make-up of the line, the installation method and the surroundings, and on the ambient temperature (sub-section 4.4.1.4). A riser running 6 m vertically inside a closed shaft does not have the same capacity as the same cable laid freely on a cable tray — the installation method is part of the calculation, not cosmetics.

Third, the rating. For domestic installations, table 4.11 (sub-section 4.4.1.4) caps the maximum rated current of the protective device per conductor cross-section:

Conductor cross-section	Maximum rated current of the fuse	Maximum rated current of the circuit breaker
1.5 mm²	10 A	16 A
2.5 mm²	16 A	20 A
4 mm²	20 A	25 A
6 mm²	32 A	40 A
10 mm²	50 A	63 A
16 mm²	63 A	80 A
25 mm²	80 A	100 A
35 mm²	100 A	125 A

That table is a ceiling, not a recommendation. It says what rating a cross-section will tolerate — not which cross-section is right for your riser. The additional condition sits in sub-section 4.4.3.2: the rated current I_n of the overload protective device must be at least the design current I_B of the circuit and lower than the current-carrying capacity I_Z of the line it protects; its conventional operating current I_f does not exceed 1.45 times I_Z.

Trade practice, not regulation: in a Belgian dwelling a floor riser typically lands on 6 mm² with a C32 breaker, or on 10 mm² with a C40, and the sub-board's load-break switch is executed as 40 A — the smallest common size that covers the range and that satisfies the 40 A floor of 5.3.5.1 b anyway. The AREI/RGIE prescribes none of these values; it only caps them.

Does the riser have to be protected in the main board?

In principle yes, and at its origin. A short-circuit protective device is placed at the origin of every circuit made up of electrical lines with equivalent characteristics (sub-section 4.4.2.2 point a). For overload the principle is the same: the device is placed, as a rule, where a change of cross-section, nature, installation method or make-up reduces the current-carrying capacity of the conductors (sub-section 4.4.3.1) — that is, precisely where the main board's busbar continues into a 6 mm² cable.

The regulation provides three derogations that genuinely occur in installations spread over several levels:

Upstream protection suffices. The short-circuit protective device may be omitted at the origin of a circuit, provided it is verified that the device placed upstream can still perform its function (4.4.2.2 a).
Three metres of latitude. The protective device may sit on the line up to 3 m from the origin of the circuit, provided that stretch contains nothing liable to cause particular heating — connections, branches, reductions in cross-section, switchgear — and is not placed close to combustible materials (4.4.2.2 b).
The sum of the branches. Overload protection may be dispensed with for an electrical line supplying several branches that are individually protected against overload, provided the sum of the rated or setting currents of those branch devices is lower than the rated or setting current of the device that would protect the line in question against overload (sub-section 4.4.3.3).

It is the third derogation that gets misread on risers. It does not allow the feeder to be left unprotected — it allows the overload protection to be omitted where the sum of the downstream ratings could never overload the line anyway. Short-circuit protection remains due. In a sub-board holding eight C16 and two C20, the ratings add up to 168 A; a 6 mm² riser does not fall under that exemption.

Do not forget the identification: circuits connected upstream of the main switch of the distribution and switching board must be identified as such (sub-section 3.1.3.1).

Does the AREI/RGIE require selectivity between main and sub-board?

For an ordinary domestic installation: no. The word selectivity appears in the AREI/RGIE only in the context of safety installations and critical installations. There it says that the correct operation of a circuit with safety loads, respectively of a safety circuit, may not be affected by an electrical fault in another circuit, and that "this requires selectivity between the protective devices" (sub-sections 5.5.7.1 point a and 5.5.7.2; identical wording for critical installations in chapter 5.6). For the riser to the bedroom floor of a single-family house there is no equivalent prescription.

What the regulation does govern is the coordination of protective devices placed in series (sub-section 4.4.1.3) — and that is a different thing from selectivity. Where several protective devices are placed in series, they may be coordinated so that, in the event of a downstream short circuit, the upstream device limits the energy passing through the downstream devices to a value that those devices and the lines they protect can withstand. Where the devices in series are circuit breakers, this accompanying protection has a name of its own: back-up protection — the French text calls it filiation, the German one Backup-Schutz. To determine its characteristics you have to request the manufacturers' back-up protection tables, drawn up in accordance with the product standards for circuit breakers (4.4.1.3). In non-domestic installations, the individual identification of the distribution and switching board must even state that the technique is being used (sub-section 3.1.3.3 point b).

The difference in one sentence: back-up protection lets a downstream breaker survive a short circuit it could not clear on its own, and gives it a reinforced ultimate breaking capacity. Selectivity makes sure a fault upstairs does not put the whole house in the dark. The first is a safety matter and is regulated; the second is a comfort and availability matter and, outside safety installations, a design decision.

Trade practice: grading — slower and larger upstream, faster and smaller downstream, and for RCDs additionally through sensitivity and time delay — is common and sensible in multi-storey installations. But it is an application of IEC 60364-5-53 and of manufacturer data, not an AREI/RGIE obligation. Anyone defending it in an inspection report as an "AREI requirement" is citing a provision that does not exist.

May one circuit supply several floors?

Yes. The AREI/RGIE knows no rule limiting a final circuit to one level. A lighting circuit feeding the hall, the stairwell and the upstairs landing together is permitted — and in Belgian terraced houses it is the normal case, because the stairwell belongs geometrically to both levels.

All the quantity and assignment limits nevertheless remain fully applicable, and they count across floors:

Limit	Value	Reference
Single or multiple socket outlets per final circuit	at most 8	5.3.5.2 b
Separate lighting circuits for more than two rooms and/or locations	at least 2	5.3.5.2 b
Final circuits per high or very high sensitivity RCD	at most 8	4.2.4.3 b
RCD placed at the origin of the electrical installation	at most 300 mA	4.2.4.3 b
Fixed appliances with a common operating device in a mixed circuit	count as 1 socket	5.3.5.2 b

The third and fourth rows work together the moment a sub-board enters the picture. Immediately downstream of the protective device placed at the origin of the electrical installation, at least one residual current device of high or very high sensitivity is placed, to which are connected at least the socket outlets not intended for fixed appliances, the lighting, the locations containing a bath and/or a shower, and the washing machines, tumble dryers and dishwashers — with at most eight final circuits per RCD (4.2.4.3 b). A bathroom on the upper floor fed from the board that sits there therefore needs that assignment there too; the 300 mA device at the origin of the installation does not replace it.

Two practical limits follow from the principle rather than from an article: a final circuit spread over three levels becomes long, and voltage drops in electrical lines are to be limited to the values described in the rules of good practice (section 5.2.5 — the regulation itself quotes no percentage there). And a circuit scattered over three levels makes fault-finding awkward, because that part of the installation can no longer be isolated in one place. How to establish the corresponding lengths defensibly is covered in Cable routes and cable lengths.

How do I take the riser through the floor slab?

The penetration itself is regulated. Where electrical lines pass through floors, they are protected at the level of the finished floor against mechanical damage and against liquids that may be spilled on the finished floor. Where the penetration is made with conductors run in conduits, those conduits are watertight and their upper end projects above the floor — at least as high as the skirting boards, if any, and at least 10 cm (sub-section 5.2.1.5). The same provision requires special precautions against water ingress and condensation for penetrations between rooms that may differ appreciably in humidity; unsealed conduits are then inclined towards the damper room.

For the vertical run inside a storey, the installation zones apply: electrical lines embedded without conduit in the walls of rooms follow horizontal and vertical routes only, the vertical runs lying as close as possible to a corner of the room or between 10 and 20 cm from door frames or casings (sub-section 5.2.9.10 point b). Horizontal runs lie between 25 and 35 cm from the floor or the ceiling.

Cable trunking is an installation method named as such by the AREI/RGIE (sub-section 5.2.2.1 point h.1, figure 5.11) — and the right choice as soon as several lines take the same vertical route. Two points to watch:

Where electrical lines of circuits at different voltages are used in a cable tray or in cable trunking, the connections for joints, terminations or branches are made in compartments that separate the lines at different voltages (sub-section 5.2.9.6).
Insulated conductors and cables installed in bunches or in a flat formation have at least characteristic F2, or at least class C_ca — and this applies regardless of the distance over which they are actually bunched (sub-section 5.2.7.3). A riser shaft with six cables is exactly such a bunch.

What is not covered here: the fire-stopping of the shaft between storeys. The AREI/RGIE imposes fire resistance on lines and boards only in the context of safety installations and critical installations (chapters 5.5 and 5.6). Compartmentation of a residential building belongs to construction law — the basic standards on fire prevention and the regional prescriptions — not to the electrical regulation. So do not invent an AREI article for it; where in doubt, refer to the project's fire safety file.

How is equipotential bonding run across several levels?

There are two equipotential bonds, and only one of them travels through the whole building.

Main equipotential bonding is building-wide. The main protective bonding conductor has a cross-section at least equal to half that of the largest protective conductor of the installation, the earthing conductor excluded, with a minimum of 6 mm² in copper; its cross-section may be limited to 25 mm² in copper, or to the electrically equivalent cross-section in another metal (sub-section 5.4.4.1 point a). This conductor carries green-and-yellow insulation and follows the prescriptions applicable to protective conductors (point b).

Supplementary equipotential bonding, by contrast, is expressly local. In a location containing a bath and/or a shower, it locally connects all exposed conductive parts of the electrical equipment and all simultaneously accessible extraneous conductive parts situated in that location (sub-section 7.1.4.4). A bathroom on the upper floor therefore gets its own supplementary bonding; it is not brought up from the ground floor. The cross-sections: at least half that of the protective conductor connected to an exposed conductive part, and in no case less than 2.5 mm² for mechanically protected conductors, 4 mm² for those that are not (sub-section 5.4.4.2 point a).

The practical consequence for the riser: the protective conductor goes up in the same cable; extraneous conductive parts — water and heating pipes, metal structures — are bonded where they enter the building, via the main equipotential bonding, and not a second time per floor. Which earthing arrangement sits behind all of this is covered in Earthing: TT or TN-S.

How must the floors appear on the position plan and the single-line diagram?

The AREI/RGIE separates the two documents cleanly, and that separation decides where a storey becomes visible at all.

The position plan indicates the position of the distribution and switching boards, the connection boxes and junction boxes, the socket outlets, the lighting points, the switches, the fixed machines and appliances, and the sources mentioned on the single-line diagram (sub-section 3.1.2.3 point a). The plural in "distribution and switching boards" is the decisive detail: a sub-board on the upper floor must be located on the position plan. A diagram alone is not enough.

The single-line diagram carries the characteristics of the electrical lines — type, cross-section, number of conductors —, the installation methods, the type and characteristics of the residual current and overcurrent protective devices, the switches, the connection and junction boxes, the socket outlets, the lighting points, the fixed machines and appliances, and the sources (sub-section 3.1.2.2 point a). For a riser that means, concretely: type, cross-section, number of conductors and installation method are mandatory entries, not an extra.

As for identification: on the single-line diagram every elementary circuit is identified by a capital letter; every lighting point, socket outlet and control unit by a number giving the order in which they are met within the elementary circuit, starting from the overcurrent protective device upstream. On the position plan those same elements carry the letter of their circuit and the sequence number assigned on the diagram (sub-section 3.1.2.1 point a, figures 3.1 and 3.2). This identification is floor-independent — a circuit C running over two levels is called C on both levels.

Every distribution and switching board additionally carries a clear, conspicuous and indelible individual identification, with the supply voltage clearly and conspicuously indicated (sub-section 3.1.3.3 point a), and the control, protection and isolation devices of circuits carry individual identifications, unless any possibility of confusion is ruled out (sub-section 3.1.3.1).

What the AREI/RGIE does not prescribe: that a separate sheet exists per floor, or that a separate diagram is drawn per board. Both are drawing practice — a very well-established practice, because a position plan with two levels superimposed becomes unreadable. How the two documents delimit each other is covered in Single-line diagram vs. position plan; the make-up of a position plan is treated in Drawing a situation plan.

Does every floor need a smoke detector?

That is not an AREI question. The AREI/RGIE does not require smoke detectors for domestic installations. The obligation comes from regional housing law: Flanders, Wallonia and Brussels each regulate independently how many detectors go where, and the requirements differ both in the number per level and in their scope for existing dwellings.

For multi-storey planning only the consequence matters: the detector evidence does not belong in the AREI inspection report but in the regional conformity, and where the detectors run on 230 V, their circuit appears on the single-line diagram like any other. The regional rules in detail are in Smoke detector obligations in Belgium — there and not here, so that only one maintained version exists.

What applies if I convert a floor later on?

A converted attic is almost always a significant extension. The AREI/RGIE defines it as a modification or extension of an electrical installation that has an additional impact — not yet covered by a conformity inspection — on the safety of persons or property, and it expressly cites "the addition of a circuit in a domestic installation" as an example (section 2.11.2, definitions). A new sub-board with six circuits meets that several times over.

Three consequences follow:

Inspection before commissioning. Any significant modification or extension undergoes a conformity inspection before that modification or extension is put into use; this inspection is limited to the added or modified parts of the installation (sub-section 6.4.7.3). The old ground-floor installation is therefore not inspected automatically. Modifications or extensions that have an impact on an unmodified part must nevertheless be mentioned in the conformity inspection report.
300 mA for the whole installation. In the case of a significant modification or extension in an old domestic electrical installation, the entire electrical installation is protected by at least one residual current device with a rated residual operating current of at most 300 mA (sub-section 4.2.4.3 point b). That is the prescription which regularly makes an attic conversion more expensive than budgeted.
The position plan travels with it. Any modification or extension made to a domestic electrical installation is shown on the position plan, which gives the existing situation of the installation's components at all times. Any older part whose on-site execution began before 1 October 1981 and which appears on the single-line diagram is marked "older part" (sub-section 3.1.2.1 point a).

For modifications that cannot be qualified as significant, no new single-line diagram is required; a brief description of the modification, stating the name, capacity and address of those responsible for carrying out the work, dated and signed by them, is sufficient (3.1.2.1 a). The position plan must nevertheless be kept current. The full sequence for a new build is set out in the New-build single-line diagram checklist.

Single-family house or apartment building — does that change the answer?

Yes, and on a point that is often overlooked. As long as all the storeys belong to one dwelling unit, the whole thing is a single domestic installation: one single-line diagram, one position plan, one inspection, and the quantity limits of 5.3.5.2 b apply to that one unit.

The moment a dwelling unit of its own appears per floor, several domestic installations appear — each with its own main distribution and switching board with a general load-break switch of at least 40 A (5.3.5.1 b), its own diagram, its own position plan and its own inspection. The eight sockets per final circuit then count per dwelling unit, not per building.

For the common parts — stairwell lighting, bell installation, outdoor lighting, meter room — there is an explicit relaxation: by way of derogation from the prescriptions for non-domestic installations, it is permitted to limit oneself, for the diagrams, plans and documents of the common parts of a residential complex, to the prescriptions applicable to a domestic installation (sub-section 3.1.2.1 point e). The same goes for the identification of the corresponding distribution and switching boards (sub-section 3.1.3.3 point c). In practice: for the stairwell board a single-line diagram in the familiar domestic format is enough — you do not have to document prospective short-circuit currents, impedances or utilisation categories, as 3.1.2.2 b would otherwise require.

How do I align the floors in PlanElec?

In PlanElec, floors are not separate drawings but levels of one shared building model. You create them, order them, and copy the outer contour or the building structure from one level to the next; a shared building origin keeps the plans superimposable, and a reference overlay shows the neighbouring floor at an adjustable opacity.

The alignment itself runs on point pairs: you place the same distinctive point first in the current plan and then in the displayed reference plan. From two point pairs onwards, offset and rotation are derived automatically. PlanElec then reports the mean and the largest deviation in centimetres, as well as the residual deviation per point pair; the arrow keys move by 1 cm, with Shift by 10 cm. The scale stays fixed — the alignment is rigid and never distorts a floor to pull points together.

The vertical connection is an element in its own right, available as staircase, shaft and riser zone. A staircase is drawn on one floor and appears on the neighbouring floor as the same editable element, mirrored — solid up to the cut line, dashed beyond it. Changes made to the projected twin are written back to the source floor. A point pair can be taken straight from a staircase or a shaft.

For the electrical side, more depends on this than it first appears:

Switch chains are project-wide. While drawing, you continue a chain via the floor selector; the display states how many members are on this floor and how many in total, across how many floors.
Circuit assignment works across floors: loads on several floors can be assigned together to an existing circuit breaker, and the selection survives a floor change.
Physical cable routes do run across floors, but in two kinds of leg: floor legs are drawn and edited locally on their own level, while the vertical leg is chosen through a connector instead of being drawn. The vertical length is derived from the storey heights and the horizontal offset as long as it has not been measured — and it feeds into the cable length and therefore into the voltage drop calculation. Storey heights are marked as an assumption or as a confirmed value; the default is 2.50 m clear height and 0.30 m slab thickness.
Sub-distribution boards are created as boards of their own, with a supply line from the upstream board. PlanElec creates the feeder circuit breaker in the supplying board, hangs the sub-board's main switch beneath it, and proposes a rating and cross-section based on the expected load and a diversity factor of 0.7. A board is assigned to a floor by the act of placing its symbol in that floor's plan.

On export, each floor gets its own page of the position plan with its own title block; floors without drawn walls are skipped. The single-line diagram is built as one sheet per board, main board first, and a single board may occupy several A4 pages. Between the sheets, PlanElec places cross-references in both directions: on the main board's sheet, the outgoing way to the sub-board carries that sub-board's sheet number, and on the sub-board's sheet, the incoming supply carries the sheet number of the supplying board.

What the AREI self-check does not do here

The self-check is indicative and only evaluates supported rules on the basis of the data entered. For multi-storey installations that means, concretely:

What it checks:

That a supply line between two boards has a protective device of its own in the upstream board, points to an existing target board, and is consistently assigned on both sides. If one of these is missing, it is an error, not a remark.
The voltage drop using the actual cable length, including the vertical legs of routes that cross floors. If the length is missing, the result is not an error but a non-blocking notice that the entry is absent.
Grading between upstream and downstream residual current devices — explicitly as a practice recommendation under IEC 60364-5-53, not as an AREI rule, and therefore as a warning you can override.
Smoke detector coverage per floor — likewise an overridable warning and explicitly a pointer to regional law, not to the AREI. Where bedrooms or hallways are recorded as a room type, PlanElec reports room by room; only where no such room type is recognisable on a floor does the per-floor rule act as a fallback.

What it does not check:

The cross-section of the riser. The line between two boards is maintained as a circuit with a protective device, but not as a cable segment of its own with a cross-section. The cross-section shown when the board is created is a preview of the calculation, not a stored value — it therefore appears neither in the cross-section check nor in the voltage drop calculation.
The ampere grading between the feeder protection and the sub-board's main switch. That is a deliberate choice: the coordination of protective devices placed in series runs, per 4.4.1.3, on let-through energy and breaking capacity, and therefore on the manufacturer's back-up protection tables, not on the rated current.
Short-circuit selectivity between circuit breakers. No rule addresses it — and under the AREI/RGIE there is no obligation either, outside safety and critical installations.
The riser zone as a concept. It is a type of vertical connector in the plan, serving the cable routing; no check rule evaluates it.
Fire-stopping, compartmentation and shaft closure. That lies outside the AREI/RGIE and outside the self-check.
It replaces neither measurement nor inspection. The official assessment rests exclusively with an approved body.