Electrical and Controls Work for Renewable Heating
Core concepts
Heat pump electrical work spans supply, protection, controls and metering. Candidates must understand diversity and maximum demand, correct protective device selection (MCB/RCBO types, RCD requirements), earthing and bonding, and cable sizing for the heat pump and immersion/backup heater. Know the difference between a dedicated heat pump supply and shared circuits, and the need for isolators local to the unit. Controls include weather compensation, room influence, set-back, DHW priority, legionella scheduling and smart tariff/load-shifting inputs. Understand how open protocols (e.g. Modbus, OpenTherm-style interfaces) and manufacturer controllers integrate, and how to set up heating curves. Three-phase versus single-phase supply, inrush currents and soft starts also matter. Metering, monitoring and the ability to verify performance (electricity in versus heat out) are part of good practice.
Traps
Questions often test RCD type and rating, or whether a heat pump needs a dedicated circuit. Watch for confusion between MCB and RCBO, and between earthing and bonding. Another trap is assuming a controller's default heating curve suits the building - it must be adjusted. Candidates frequently forget that backup/immersion heaters add to maximum demand and may need separate protection.
Worked example / rule of thumb
A single-phase 8 kW heat pump drawing about 2.5 kW electrical at design, plus a 3 kW immersion, gives a combined demand of 5.5 kW ≈ 24 A at 230 V. Size the circuit and protective device for the combined load, not just the compressor. Rule of thumb: allow for inrush and ensure the RCD type suits the inverter/electronic load.