Electrical Connection in Heat Pump Installation
An electrical connection in heat pump installation is the essential link between the heat pump, the building’s power supply, and its control systems. It allows the unit to receive the correct voltage, operate the compressor and auxiliary components safely, communicate with sensors or smart energy systems, and meet electrical standards in Austria, Germany, Switzerland, and the wider EU. Because heat pumps are high-load appliances, this connection must be planned by a qualified electrician with proper cable sizing, protective devices, earthing, control wiring, and grid operator approval. A correct electrical connection improves safety, prevents system faults, protects warranty coverage, supports SG Ready or PV integration, and ensures the heat pump can run reliably, efficiently, and legally from the first commissioning.
What Is Electrical Connection in Heat Pump Installation?
Electrical connection in heat pump installation is the process of linking a heat pump unit to a building’s power supply system. This includes sizing and routing power cables, installing protective devices, wiring control circuits, and establishing a compliant, safe connection to the electrical grid. The electrical connection enables the heat pump to draw power, run its compressor and auxiliary components, and communicate with building control systems.
Every heat pump installation depends on a correct electrical connection. Without it, the system cannot start, cannot operate safely, and cannot comply with national and European electrical standards.
Core Purpose
The electrical connection serves three primary functions:
- Power delivery — Supplies the heat pump with the voltage and current it needs to operate the compressor, pumps, fans, and controls.
- System protection — Provides overcurrent, residual current, and short-circuit protection for both the unit and the building.
- Control integration — Enables communication between the heat pump controller, energy management systems, smart-grid interfaces, and external sensors.
Why Electrical Connection Is Needed
Heat pumps are high-load electrical appliances. A standard air-to-water heat pump for residential use draws between 2 kW and 10 kW of electrical power. Brine-to-water and water-to-water systems can draw more.
Incorrect wiring causes compressor failure, nuisance tripping, grid instability, and fire risk. Regulatory bodies across Austria (ÖVE/ÖNORM), Germany (VDE/DIN VDE), and Switzerland (SEV/NIV) mandate certified electrical work before a heat pump can be commissioned. Grid operators require notification or approval before connection, especially for systems above 3.68 kW single-phase draw.
The need for correct electrical connection is driven by:
- High starting currents (inrush) during compressor startup
- Continuous high-load operation over long runtime periods
- Sensitivity of electronic control boards to voltage fluctuations
- Legal liability and insurance requirements
- Warranty conditions set by the manufacturer (e.g., iDM Energiesysteme GmbH)
Key Features of the Electrical Connection System
Power Supply Configuration
Definition: The power supply configuration defines whether the heat pump operates on single-phase (230 V, 50 Hz) or three-phase (400 V, 3~/N/PE, 50 Hz) power.
Purpose: Matches the electrical demand of the compressor and auxiliaries to available grid capacity.
Benefits:
- Three-phase connection reduces starting current per phase
- Balances load across all three phases of the grid
- Required for heat pumps above approximately 3.5 kW electrical input
Practical application: Most iDM heat pumps with a heating capacity above 8 kW require a three-phase 400 V connection. Compact residential units may operate on single-phase 230 V, but this must be confirmed in the technical datasheet before installation.
Cable Sizing and Routing
Definition: Cable sizing is the process of selecting the correct cross-sectional area of supply cable based on the heat pump’s rated current, cable length, installation method, and ambient temperature.
Purpose: Prevents resistive heating in cables, voltage drop, and protection device miscoordination.
Benefits:
- Ensures full voltage at the heat pump terminals
- Prevents premature aging of cable insulation
- Enables protection devices to operate correctly under fault conditions
How to determine cable size:
| Heat Pump Electrical Input | Typical Rated Current | Minimum Cable CSA (Cu, B2) |
|---|---|---|
| Up to 3.5 kW (1~/N/PE) | Up to 16 A | 2.5 mm² |
| 3.5–7 kW (3~/N/PE) | Up to 16 A per phase | 2.5 mm² |
| 7–14 kW (3~/N/PE) | Up to 25 A per phase | 4 mm² |
| 14–22 kW (3~/N/PE) | Up to 35 A per phase | 6 mm² |
Values are indicative. Always calculate to IEC 60364-5-52 and local standards.
Cable routing considerations:
- Maintain separation between power and control cables (minimum 100 mm, or use shielded control cable)
- Use conduit or cable duct in exposed areas
- Avoid routing near heat sources
- Follow manufacturer cable entry points and strain relief requirements
Protective Devices
Definition: Protective devices are electrical components that interrupt the circuit under fault conditions. They protect the heat pump, the wiring, and the building from overcurrent, short circuits, and earth faults.
Purpose: Limits damage and prevents fire or electric shock in fault conditions.
Benefits:
- Complies with IEC 60364, VDE 0100, ÖVE/ÖNORM E 8001, and SEV 1000
- Protects the compressor from sustained overcurrent
- Provides safe isolation point for service and maintenance
Required protective devices for heat pump circuits:
- Miniature Circuit Breaker (MCB): Protects against overload and short circuit. Characteristic curve B or C depending on compressor type. Sized to rated current with appropriate trip margin.
- Residual Current Circuit Breaker (RCCB / FI-Schalter): Detects earth leakage current. Type A minimum for heat pumps with electronic speed control (inverter). Type B required where DC leakage is possible (mandatory in many DACH installations for inverter-driven compressors per IEC 62423).
- Surge Protection Device (SPD): Protects control electronics from transient overvoltage. Especially important for outdoor-mounted monobloc units.
- Isolator / Main Switch: Provides lockable isolation for service. Must be accessible without entering a restricted space.
Regulatory note: In Austria, ÖVE/ÖNORM E 8001 Part 1 and Part 6 apply. In Germany, DIN VDE 0100-701 and the Niederspannungsanschlussverordnung (NAV) govern the grid connection process. In Switzerland, the Niederspannungsinstallationsnorm (NIN 2020) is the governing standard.
Earthing and Equipotential Bonding
Definition: Earthing connects the metal enclosure of the heat pump to the protective earth (PE) conductor of the building’s electrical system. Equipotential bonding connects all metallic parts of the heating system — pipework, heat exchanger housing, buffer tank — to the same earth reference.
Purpose: Prevents dangerous touch voltages on accessible metal parts if an internal fault occurs.
Benefits:
- Ensures RCD trips within the required time under fault conditions
- Prevents electrochemical corrosion caused by stray currents
- Required for all Class I equipment under IEC 61140
Practical application: The PE conductor must be continuous from the distribution board to the heat pump terminals. Outdoor units must have the earth connection made before energisation. For split systems with refrigerant lines, the indoor and outdoor units must both be individually earthed.
Control Wiring and Low-Voltage Circuits
Definition: Control wiring connects the heat pump controller to external components including room thermostats, weather compensation sensors, domestic hot water sensors, buffer tanks, zone valves, and energy management systems.
Purpose: Enables the heat pump to receive demand signals and adjust output accordingly.
Benefits:
- Allows modulating operation based on actual building demand
- Enables integration with smart home systems and building energy management
- Supports time-of-use tariff optimisation
Common control connections in iDM heat pump installations:
| Signal | Description | Cable type |
|---|---|---|
| Outdoor temperature sensor | Weather compensation input | 2-wire, shielded, 0.75 mm² |
| Domestic hot water demand | DHW priority signal | 2-wire, 24 V or potential-free contact |
| Room thermostat / room controller | Heating/cooling demand | 2-wire or bus (iDM Navigator system) |
| SG Ready interface | Smart grid load management | 2-wire, potential-free contact |
| EVU block / utility contact | Utility company load control | 2-wire, potential-free contact |
| BMS / Modbus / CAN | Building management integration | Shielded twisted pair or specific bus cable |
SG Ready Interface and Smart Grid Integration
Definition: SG Ready is a German/Austrian heat pump industry standard (defined by BWP – Bundesverband Wärmepumpe) that defines four operating modes controlled via two external contacts. It allows grid operators and energy management systems to signal the heat pump to shift load.
Purpose: Enables demand-side management. The heat pump can increase load when renewable electricity is abundant (e.g., midday PV surplus) and reduce load when the grid is stressed.
SG Ready operating modes:
| Mode | Contact 1 | Contact 2 | Heat Pump Behaviour |
|---|---|---|---|
| 1 – Blocked | Closed | Open | Compressor blocked (EVU lock) |
| 2 – Normal | Open | Open | Standard operation |
| 3 – Increased | Open | Closed | Elevated set-point, increased load |
| 4 – Maximum | Closed | Closed | Maximum operation, full load |
Benefits:
- Reduces electricity costs by running during low-tariff periods
- Integrates with photovoltaic systems for self-consumption optimisation
- Satisfies requirements for heat pump subsidies in DACH region (e.g., Austrian Klimabonus, German BEG programme conditions)
Types of Electrical Connection Configurations
Single-Phase Connection (1~/N/PE, 230 V)
Used for smaller heat pumps, typically up to 3.5 kW electrical input. Common in renovations where three-phase power is not available. Limitations include lower starting torque and higher current draw per phase.
Three-Phase Connection (3~/N/PE, 400 V)
Standard for residential and commercial heat pumps above 3.5 kW. Provides balanced load distribution. Required by most grid operators for heat pumps with compressors above 2.2 kW shaft power.
Separate Meter / Heat Pump Tariff Connection
In Austria and Germany, a second electricity meter can be installed for the heat pump circuit. This enables access to preferential heat pump electricity tariffs (Wärmepumpenstrom / Wärmepumpen-Tarif) with lower per-kWh costs. The utility retains the right to interrupt supply for up to two hours per interruption, three times per day — managed via the EVU block contact or SG Ready mode 1.
Direct Connection vs. Sub-Distribution
For large residential or commercial installations, the heat pump may be connected via a dedicated sub-distribution board (Unterverteilung). This separates the heat pump circuit from household circuits, simplifies service isolation, and provides space for all required protection devices.
Installation Process: Step-by-Step Electrical Connection
A correct electrical connection follows a defined sequence. Deviations increase risk and invalidate warranty claims.
Step 1 — Grid operator notification Submit a connection application to the local grid operator (Netzbetreiber/Netzbetreiber) before installation. Required in Austria under ElWOG, in Germany under EnWG and NAV, in Switzerland under StromVG.
Step 2 — Load assessment Calculate the heat pump’s rated current from the technical datasheet. Verify available grid capacity at the connection point. Confirm single-phase or three-phase supply.
Step 3 — Cable selection Select cable type, cross-section, and length according to IEC 60364-5-52 and local standards. Account for installation method (conduit, trunking, buried) and ambient temperature correction factors.
Step 4 — Distribution board preparation Install MCB, RCCB (Type A or B as required), and SPD in the distribution board. Label the circuit. Provide lockable isolation point.
Step 5 — Cable routing Route the supply cable from the distribution board to the heat pump. Maintain separation from control cables. Secure cable at required intervals. Install cable gland at heat pump entry point.
Step 6 — Terminal connection Connect supply conductors (L1, L2, L3, N, PE) to the heat pump terminals in the correct sequence. Verify terminal torque values from the installation manual (typical: 1.5–4 Nm for 4–16 mm² conductors). Do not over-torque.
Step 7 — Control wiring Connect sensor cables, bus cables, and external control contacts. Follow the wiring diagram in the manufacturer’s installation manual. Use shielded cable where specified.
Step 8 — Earth and equipotential bonding Verify PE continuity from distribution board to heat pump terminals. Connect pipework bonding conductor where required by local standards.
Step 9 — Insulation resistance test Before energisation, measure insulation resistance between all live conductors and earth. Minimum 1 MΩ per IEC 60364-6. Disconnect the heat pump controller before testing to protect electronics.
Step 10 — Functional test Energise the circuit. Verify supply voltage at heat pump terminals (tolerance typically ±10% of rated voltage). Test RCCB by pressing the test button. Confirm all control signals are received by the controller. Start the heat pump in service mode and observe startup sequence.
Step 11 — Documentation Complete the electrical installation certificate / Prüfprotokoll. Record measured values (insulation resistance, earth loop impedance, RCD trip time). File documentation for warranty, subsidy applications, and inspection.
Use Cases
New-Build Residential Installation
A new build with an iDM TERRA air-to-water heat pump requires a dedicated three-phase circuit from the main distribution board, SG Ready integration with the building’s photovoltaic inverter, and a separate heat pump tariff meter. The electrical connection is planned alongside the building’s full electrical design.
Renovation / Boiler Replacement
Replacing a gas boiler with a heat pump in an older building often requires a main fuse upgrade (Hauptsicherungserhöhung) and installation of a Type B RCCB if the existing board only carries Type AC devices. The electrician must assess the existing wiring before installing new circuits.
Commercial / Multi-Family Residential
Large heat pumps (above 30 kW) require three-phase connection, dedicated metering, power factor correction consideration, and often a formal grid connection study. Modbus or BACnet integration connects the heat pump to the building management system.
Heat Pump with PV System
When a heat pump operates alongside a photovoltaic system, the SG Ready interface or Modbus connection enables the energy manager to direct surplus PV power into the heat pump, increasing self-consumption. This is a primary use case for iDM Navigator energy management functionality.
Benefits of a Correctly Executed Electrical Connection
| Benefit | Description |
|---|---|
| Operational reliability | Correct cable sizing and protection prevents nuisance tripping and compressor damage |
| Energy cost reduction | SG Ready and tariff meter access reduce per-kWh costs by 20–40% in favourable tariff structures |
| Regulatory compliance | Meets ÖVE, VDE, SEV, and IEC requirements for safe electrical installation |
| Subsidy eligibility | Austrian Klimabonus, German BEG, Swiss cantonal subsidies require compliant, certified installation |
| Warranty protection | Manufacturer warranty is conditional on installation to published standards |
| Longevity | Correct earthing and surge protection extends the life of control electronics |
| Smart grid readiness | SG Ready and Modbus connections prepare the system for future energy management expansion |
Selection Criteria for Electrical Components
When specifying components for the electrical connection, consider:
For protective devices:
- RCCB type must match compressor technology: Type A for standard inverter drives, Type B where high-frequency DC leakage is possible
- MCB trip characteristic: Curve B for normal resistive loads, Curve C or D where high inrush current occurs
- Short-circuit rating (kA) must match or exceed the prospective short-circuit current at the installation point
For cables:
- Use cables rated for continuous outdoor use if routing outside or through unheated spaces
- Halogen-free (LSOH/HFFR) cables recommended for indoor sections
- Shielded control cable mandatory for bus systems and sensor circuits longer than 10 m
For the SG Ready / control interface:
- Verify the heat pump controller supports SG Ready as standard or as an option
- Confirm potential-free contact rating matches the energy management system’s output specifications
- For Modbus integration, confirm RS485 interface availability on the heat pump controller
Comparison: Single-Phase vs. Three-Phase Electrical Connection
| Criterion | Single-Phase (230 V) | Three-Phase (400 V) |
|---|---|---|
| Typical heat pump size | Up to 8 kW heating capacity | 8 kW and above |
| Phase imbalance | High — full load on one phase | Low — balanced across three phases |
| Starting current | Higher relative to phase capacity | Lower per phase |
| Grid operator approval | Often automatic below 3.68 kW | Notification/approval required above 3.68 kW |
| Tariff options | Standard household tariff | Heat pump tariff often available |
| Cable cost | Lower (fewer conductors) | Higher |
| Suitability for expansion | Limited | Suitable for battery storage, EV charger additions |
Integration with Other Systems
Integration with Photovoltaic Systems
The heat pump’s SG Ready input or Modbus interface connects to the PV inverter’s energy manager. When PV generation exceeds household demand, the energy manager activates SG Ready mode 3 or 4 to increase the heat pump’s set point and store thermal energy in the buffer tank or DHW cylinder. This increases PV self-consumption without additional battery storage.
Integration with Battery Storage Systems
A home energy management system (HEMS) coordinates between the heat pump, battery, and grid. The electrical connection must include the correct communication interfaces. In iDM installations, the Navigator energy manager handles this coordination via its integrated smart grid functionality.
Integration with Building Management Systems (BMS)
Commercial heat pump installations connect to BMS via Modbus RTU (RS485), Modbus TCP/IP, or BACnet. The electrical connection provides the physical layer: shielded twisted-pair cable for RS485, or a standard network connection for TCP/IP-based protocols. Correct cable shielding and termination are critical for signal integrity.
Integration with EV Charging
In homes with both a heat pump and an EV charger, the total electrical load may exceed the existing main fuse rating. Load management systems, connected to both the heat pump and the EVSE (Electric Vehicle Supply Equipment), dynamically allocate available current. This requires both systems to expose a compatible load management interface.
Integration with District Heating or Hybrid Systems
In hybrid systems combining a heat pump with a gas or pellet boiler, the control wiring connects the heat pump controller to the boiler’s demand input. The heat pump operates as the primary generator; the boiler activates above a defined outdoor temperature threshold (bivalent point). Wiring must account for the safety interlocks between both systems.
A correct electrical connection is the foundation of a safe, efficient, and grid-compliant heat pump installation. It connects the heat pump to the power supply, protects the system from electrical faults, enables smart control through SG Ready or Modbus, and ensures compliance with IEC, VDE, ÖVE/ÖNORM, and SEV requirements. For homeowners, installers, and planners, proper cable sizing, protective devices, earthing, control wiring, and grid operator approval are not optional details; they determine reliability, warranty protection, subsidy eligibility, and long-term operating cost. In short, the electrical connection turns the heat pump from a standalone appliance into a safe, intelligent, and future-ready part of the building’s energy system.
