Heat Pump on a Single-Line Diagram: Showing the Circuit and Equipment Correctly

On the single-line diagram, you draw a heat pump the way it is actually connected: every outgoing way with its circuit reference, overcurrent protection, residual current device (RCD), cable and electrical rating – separately for the outdoor unit, indoor unit and backup heater whenever they are supplied separately. A single box saying “8 kW” is not enough. Depending on the system, the installation includes an outdoor unit, indoor module, electric backup heater, circulation pumps, controls or a domestic hot-water cylinder, supplied together or through several circuits. The diagram shows the installed electrical structure, not the simplified hydraulic sketch from the brochure.

AREI Book 1 V06 (the Belgian wiring regulations) sets no brand-specific heat-pump symbol and no universal RCD type. The general rules for circuits, protection, cables and documentation apply together with the electrical data of the exact device. Keeping those two apart cleanly avoids the typical mistakes.

Collect the electrical data first

Start with rating plates, datasheets and the distribution board, not with drawing. For every electrically supplied unit, record:

• exact equipment designation and function;
• single- or three-phase supply and rated voltage;
• rated current or the protection the manufacturer requires;
• inverter or variable-frequency technology, where present;
• required residual-current protection and possible DC fault components;
• cable type, number of conductors, cross-section and route;
• local isolator or maintenance switch, if actually installed;
• separate supply for an electric backup heater, crankcase heater, circulation pump or controls.

A datasheet saying “thermal output 8 kW” answers none of these questions. Thermal output, electrical input power and connection rating are different quantities. On the single-line diagram, the electrical execution is what counts.

One device or several circuits?

A compact monobloc unit often has a single supply to the outdoor unit. A split system frequently supplies the outdoor and indoor units separately. An integrated backup heater runs through the same connection or needs its own, more heavily loaded circuit. Some controls are fed from the indoor unit; others have their own protection.

So do not draw this generic chain by default:

Board → circuit breaker → heat pump

A real installation may look like this:

Main board
├─ circuit HP1 → protective device → cable → outdoor unit/inverter
├─ circuit HP2 → protective device → cable → indoor unit/controls
└─ circuit HP3 → protective device → cable → electric backup heater

HP1, HP2 and HP3 are just a readable example. In the project, you follow the existing circuit logic: AREI 3.1.2.1 a identifies elementary circuits by a capital letter, and the situation plan repeats the letter and sequence number from the single-line diagram.

What belongs on each outgoing way?

The outgoing way is traceable from the board to the load. Document at least:

1. circuit reference;
2. type, number of poles and rated current of the overcurrent protection;
3. upstream RCD with rated residual current and type;
4. cable or conductor type, number of conductors and cross-section;
5. phase assignment for a polyphase supply;
6. an unambiguous equipment name, such as “heat pump outdoor unit”;
7. relevant electrical power or rated current;
8. local isolator, contactor or load-management component, if part of the fixed installation.

For household installations, AREI Table 4.11 (Subsection 4.4.1.4) caps the rated current of the circuit breaker per cross-section, for example 20 A for 2.5 mm² and 25 A for 4 mm². Still, the relationship between cable cross-section and breaker does not follow from appliance power alone: route length, installation method, grouping, ambient temperature, voltage drop, prospective fault current and manufacturer limits are part of the design.

RCD: no universal type for every heat pump

The regulatory classification is clear: a heat pump is a fixed appliance. AREI 4.2.4.3 b requires the high- or very-high-sensitivity group (30 mA) only for certain circuits – sockets not intended for fixed appliances, lighting, bathrooms and showers, and washing machines, tumble dryers and dishwashers. Fixed appliances such as electric heating installations may be connected directly downstream of the RCD at the origin of the installation (no more than 300 mA). If the earth electrode resistance exceeds 30 ohms, at least one RCD of no more than 100 mA per circuit or group of circuits supplements that protection.

The required type is set by the device. A heat pump with a power-electronic compressor can produce fault currents with waveforms that differ from a purely resistive load. That does not mean every heat pump needs Type B, nor that Type A is always sufficient. Check:

• the binding installation manual of the exact model;
• whether the device has integrated DC fault-current detection;
• the protective measure planned for the network and earthing system;
• selectivity and allocation relative to upstream RCDs;
• cumulative leakage currents from other loads.

The guide to RCD Type A versus Type B separates waveform capability, high immunity and time selectivity. The diagram states the protective device actually installed, not an assumption from a generic table.

Use a clear symbol and legend

Table 2.23 of AREI Book 1 V06 is explicitly a non-exhaustive symbol list. Where it has no suitable symbol, 3.1.2.1 a allows any other clearly identifiable symbol defined in the legend. One possible documentation distinguishes, for example:

• HP-O: heat-pump outdoor unit;
• HP-I: heat-pump indoor unit;
• BH: electric backup heater.

Each abbreviation stays the same throughout the dossier and never also means a hydraulic pump or heating circuit. The AREI electrical-symbol overview explains when standard symbols are enough and when a project legend is needed.

Keep the single-line diagram and situation plan in sync

The single-line diagram answers how the heat pump is connected and protected. The situation plan shows where the fixed electrical equipment is. Depending on the project, locate:

• outdoor and indoor units;
• maintenance switch or isolator;
• sub-board or control box;
• fixed backup heater;
• relevant cable routes where they matter for readability or later work.

Every location uses the same circuit reference as the single-line diagram. A hydraulic schematic supplements the dossier but replaces neither of the two electrical plans. See single-line diagram versus situation plan for the division of roles.

Common documentation mistakes

Writing only “heat pump 8 kW”

That entry often confuses thermal and electrical power. Protection, supply and cable stay unclear.

Forgetting the backup heater

A backup heater changes the electrical peak load considerably and often has its own connection. If it is part of the fixed installation, it belongs on the diagram.

Replacing manufacturer requirements with a rule of thumb

A generic RCD or breaker suggestion replaces neither the specific datasheet nor a complete protection design.

Presenting the design as as-built

Cable route, phases or equipment variant can change during installation. Before completion, you compare the diagram, board labels and the installation on site.

Final documentation check

Before handover, check:

• Do the rating plate and equipment name match the diagram?
• Are outdoor, indoor and auxiliary components complete?
• Do poles, rated current and RCD data match the installed devices?
• Are cable data and phases traceable?
• Do circuit references agree on the single-line diagram, situation plan and board?
• Are manufacturer documents and later changes in the installation dossier?

This check covers the documentation. The electrical design is done by the professional, and the required inspection by the approved inspection body.

When the diagram needs updating again

Replacing the whole heat pump is not the only trigger. Review the plan when a backup heater is added, a higher connection rating is unlocked, a single-phase unit is replaced by a three-phase one, or an external controller is permanently connected. The same applies when an installer changes the RCD, protection or cable route.

Do not simply write the new model over the old symbol. Compare:

• old and new electrical connection data;
• the existing cable and the conductors actually available;
• protective devices and manufacturer requirements;
• phase allocation and effects on the board;
• positions on the situation plan;
• revision date and related equipment documents.

If a decommissioned circuit physically remains, the documentation makes its real state clear. A load shown as active on the diagram but disconnected on site misleads just as much as a new backup heater missing from the plan.

Worked example: outdoor unit, indoor unit and backup heater

An installation consists of a three-phase outdoor unit, a separately supplied indoor unit and an electric backup heater. Do not draw a single block too quickly. Check on the delivered model and the actual wiring whether three outgoing ways exist or whether components are supplied internally from the outdoor unit. Only genuinely separate circuits get their own protection chain, cable data and reference.

For every existing way, you record the maximum electrical load from the binding manufacturer documentation, not the thermal heating output from the brochure. Add phases, neutral and protective conductor according to the real cable. A three-phase outdoor unit may sit alongside a single-phase control or indoor module; the shared function name “heat pump” hides that difference. Check the backup heater with particular care, as its connection rating and switching stages can clearly exceed the heat-pump figure.

On the situation plan, the outdoor unit, indoor unit, fixed isolation point and any separately supplied backup heater appear at their actual locations. Control, bus or sensor cables are not shown as power circuits. If they matter for maintenance, describe them clearly in the legend or manufacturer documentation, separate from the mains supply.

Account for commissioning data and operating modes

After commissioning, compare the drawn way with the rating plate, terminals, installer menu and test record. Load limitation, a blocking contact or energy management affect operation, but do not replace the necessary sizing and protection assessment. Document only settings that are actually applied, secured against unintended change and relevant to the design.

Also check operating cases that normal operation easily hides:

• defrosting with simultaneous backup heating;
• emergency or anti-legionella operation with the electric heater;
• start-up and inverter behaviour per the manufacturer;
• separate supply for a drain-pan or trace heater;
• shutdown and safe isolation for maintenance;
• restart after a supply interruption or load shedding.

This list does not set protection or cross-section on its own. It shows which input data the designer clarifies with the exact manual and installation conditions. Measurements and disconnection conditions are checked on site by the professional.

Also record which component can remain live when the main way is switched off. Some controls, communication power supplies or auxiliary devices have a different supply, and a maintenance sketch shows it. Mark isolation points as acting together only when wiring and the manufacturer concept confirm it. That way the documentation prevents a supposedly fully isolated system from still being fed by a second way.

Carry this separation into the board labelling. One collective name for several ways makes maintenance and comparison with the plan harder. Use short, unambiguous function names and the same references on the diagram, situation plan and equipment. After labelling, verify by switching off each way in turn that every label really covers the expected part. The result belongs to the as-built check, not to an unverified design assumption.

Interfaces with PV, battery and load management

A heat pump may respond to self-consumption control without becoming a load “behind the PV inverter” if the real AC topology is different. Draw energy paths as they are electrically connected and explain communication contacts or smart-grid signals separately. With backup power, also establish whether the heat pump is actually supplied from the backup board and which starting and power limits apply; an app setting does not prove it.

The official AREI/RGIE Book 1 publication provides the general diagram and safety framework. Model-specific connection values, required external protection and connection variants come from the current instructions for the exact installed equipment.

Documenting it in PlanElec

In PlanElec, you assign heat-pump components to their actual circuits, record protection and cable details, and export the single-line diagram and situation plan as PDFs. The heat pump is stored there as a permanently connected fixed appliance that may sit downstream of the main RCD. The AREI/RGIE self-check flags, among other things, a Type B-curve circuit breaker supplying a high-inrush load such as a heat pump – explicitly as a practice recommendation, not an AREI requirement. Project-specific symbols still need a clear legend. The roles are clear: the self-check shows you findings within the supported rules, the manufacturer's approval comes from the equipment documentation, and the official inspection is done by the approved inspection body.

Sources and reviewed version

The regulatory basis is the official AREI/RGIE Book 1 publication, particularly Table 2.23, Part 3 on electrical plans (3.1.2.1), Subsection 4.2.4.3 b on RCDs in household installations and Table 4.11, together with the electrical installation manual for the exact heat-pump model. Reviewed against Book 1 V06 on 5 October 2026.