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

Electrically, a heat pump is often more than one appliance. An outdoor unit, indoor module, backup resistance heater, circulation pump, controller and hot-water cylinder may use separate supplies. Other systems combine several functions behind one connection. The single-line diagram must show the electrical installation as actually built, not the simplified hydraulic drawing in a sales brochure.

AREI Book 1 V06 does not assign one universal heat-pump symbol, breaker or RCD type to every make and model. General requirements for circuits, protection, conductors and documentation apply together with the electrical instructions for the exact equipment. A dependable drawing starts by distinguishing those sources.

Collect the electrical evidence first

Before drawing, inspect the distribution board, nameplates and installation manuals. Record for every electrically supplied component:

• exact equipment reference and function;
• voltage and single- or three-phase supply;
• rated current and the maximum protective device specified by the manufacturer;
• inverter or variable-speed drive technology;
• RCD instructions and information about possible smooth-DC residual currents;
• cable type, conductor count, cross-section and actual route;
• local isolator or maintenance switch where installed;
• separate supplies for backup heat, controls, pumps or the cylinder.

A label stating “8 kW heating output” does not give the electrical input or connection rating. Thermal output and electrical demand are different values. Only the relevant electrical value belongs beside the circuit.

Decide how many circuits really exist

A monobloc unit may have one supply. A split system may feed outdoor and indoor units separately. A built-in resistance heater may share a terminal block or require a distinct, higher-current branch. Controls may be powered from the indoor unit or from their own protected supply.

Do not automatically draw this simplified chain:

Distribution board → breaker → heat pump

An installed arrangement could instead be:

Main distribution board
├─ circuit HP1 → protection → cable → outdoor unit/inverter
├─ circuit HP2 → protection → cable → indoor unit/controller
└─ circuit HP3 → protection → cable → electric backup heater

HP1, HP2 and HP3 are examples only. Follow the project’s circuit lettering and repeat exactly the same references on the situation plan.

What to show on each branch

The path from board to load should be understandable without assumptions. Include at least:

1. circuit reference;
2. overcurrent-device type, pole count and rating;
3. upstream RCD rating and type where present;
4. cable or conductor type, conductor count and cross-section;
5. phase allocation for a multiphase supply;
6. an unambiguous label such as “heat pump outdoor unit”;
7. relevant electrical power or rated current;
8. a fixed isolator, contactor or load-control device when it is part of the installation.

The relationship between cable cross-section and breaker cannot be derived from appliance power alone. Route length, installation method, grouping, ambient temperature, voltage drop, prospective fault current and manufacturer limits remain part of the full design.

RCD selection is model-specific

Power electronics driving a compressor can produce residual-current waveforms unlike those of a purely resistive load. That does not make Type B mandatory for every heat pump, nor does it mean Type A is always sufficient. Check together:

• the binding instructions for the exact model and installed options;
• any integrated smooth-DC residual-current detection;
• the earthing arrangement and planned disconnection conditions;
• selectivity and division between upstream RCDs;
• cumulative leakage from other connected equipment.

The guide to RCD Type A versus Type B separates waveform capability, high immunity and time selectivity. The diagram must state what is installed, rather than repeating a generic table.

Use a clear symbol and legend

Table 2.23 of AREI Book 1 V06 is non-exhaustive. If no standard symbol clearly describes the installed heat-pump arrangement, an unambiguous project symbol may be used when its meaning is defined in the legend. For example:

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

Keep each abbreviation consistent throughout the dossier. Do not reuse HP for a hydraulic pump elsewhere. The AREI electrical-symbol overview explains when a project legend is appropriate.

Keep the situation plan aligned

The single-line diagram explains how the heat pump is supplied and protected. The situation plan identifies where fixed electrical equipment is located. Depending on the installation, place:

• outdoor and indoor units;
• a maintenance switch or local isolator;
• a control cabinet or sub-board;
• the fixed electric backup heater;
• important fixed cable routes when needed for safe future work.

Every location must use the same circuit reference as the single-line diagram. A hydraulic schematic can supplement the dossier but cannot replace the electrical plans. See single-line diagram versus situation plan for the division of roles.

Common documentation failures

Showing only “8 kW heat pump”

That figure is commonly thermal output. It leaves the electrical supply, protection and wiring unknown.

Omitting backup heat

A resistance heater can materially increase peak demand and may have its own connection. Show it whenever it forms part of the fixed electrical installation.

Copying another model’s protection

Similar thermal ratings do not imply identical supply, RCD or breaker requirements. Use the actual manual and design calculations.

Treating design intent as as-built information

Phases, options and routes can change during installation. Reconcile the drawing, board labels and equipment on site before completing the dossier.

Final document review

Before handover, confirm that:

• equipment labels match the nameplates;
• outdoor, indoor and auxiliary supplies are all represented;
• pole counts, ratings and RCD details match installed devices;
• conductor and phase information is traceable;
• circuit references agree across board, single-line diagram and situation plan;
• manufacturer instructions and later changes remain in the installation dossier.

This is a documentation review. It does not replace electrical design, competent installation or the required inspection by a recognised inspection body.

When the diagram needs another revision

Review the documents not only after replacing the complete heat pump, but also when enabling a backup heater, changing available electrical power, moving from single- to three-phase equipment or adding a permanently wired controller. A changed RCD, breaker, cable route or phase allocation must also reach the as-built version.

Compare old and new connection data, available conductors, protection, manufacturer requirements, situation-plan locations and supporting manuals. If a disconnected circuit remains physically present, show its real status clearly. A drawing that still presents an isolated appliance as active is as misleading as one that omits a newly connected resistance heater.

Worked example: outdoor unit, indoor module and backup heater

Assume an installation has a three-phase outdoor unit, a separately supplied indoor module and electrical backup heat. Do not immediately reduce it to one block. Check the delivered model and site wiring to determine whether there are three final circuits or whether some components are supplied internally by the outdoor unit. Only genuinely separate circuits receive their own protective chain, wiring data and reference.

For each real branch, record maximum electrical input from the authoritative manufacturer documentation, not thermal output from a sales sheet. Show phases, neutral and protective conductor according to the installed cable. A three-phase outdoor unit may sit beside a single-phase controller or indoor module; the common function “heat pump” does not make those differences disappear. Review the backup heater especially carefully because its connected load and stages can exceed the compressor input by a wide margin.

Locate the outdoor unit, indoor module, fixed means of isolation and any separately supplied heater at their actual positions on the position plan. Do not present control, bus or sensor wiring as a power circuit. Where it matters for maintenance, explain it in the legend or technical documentation without mixing it with the mains supply.

Account for commissioning settings and operating modes

After commissioning, compare the drawn branch with nameplates, terminals, installer settings and test records. Load limiting, inhibit contacts and energy management may affect operation, but they do not automatically replace competent sizing and protective-device assessment. Record only settings that were actually applied, protected against unintended change and relevant to the design basis.

Review operating cases that a normal heating cycle can hide:

• defrost with simultaneous backup heat;
• emergency or hygiene cycle using the electric heater;
• starting and inverter behaviour stated by the manufacturer;
• separate supply for tray or trace heating;
• safe isolation for maintenance;
• restart following a supply interruption or load-shedding event.

This list does not prescribe one breaker, RCD or cable size. It identifies inputs the electrical designer must settle against the exact instructions and installation conditions. Measurements and disconnection performance remain on-site verification matters.

Interfaces with PV, storage and load management

A heat pump may respond to self-consumption control, but that does not place it electrically “behind the PV inverter” when the AC topology says otherwise. Draw energy paths according to the real connections and explain communications or smart-grid contacts separately. For backup power, establish whether the heat pump is actually supplied by the backup board and whether starting and power limits permit that mode. A setting visible in an app is not evidence of the wiring arrangement.

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

Documenting the system in PlanElec

In PlanElec, you can assign heat-pump components to the circuits actually installed, record protection and conductor details, and export the single-line diagram and situation plan as PDFs. Project-specific symbols still require a clear legend. The indicative self-check can flag supported data, but it does not certify AREI compliance, approve the manufacturer design or create an official inspection report.

Sources and reviewed version

The regulatory basis is the official AREI/RGIE Book 1 publication, particularly Table 2.23 and Part 3 on electrical plans, together with the electrical installation manual for the exact heat-pump model. Reviewed against Book 1 V06 on 29 August 2026.