Heat pump — electrical connection in practice

Heat pumps are being installed at a rapid pace in the Netherlands — both hybrid and fully electric variants, in homes as well as in commercial applications (for example climate control in an industrial hall or growing space). Electrically speaking, a heat pump raises a few specific points of attention that go beyond "just adding another circuit".

Its own final circuit

NEN 1010 (§510.4.2) specifies that equipment with a high connected load must, where necessary, be connected to its own, separate final circuit. A heat pump falls into that category in virtually every case: in practice a heat pump is therefore given its own circuit, separated from other domestic or commercial loads.

Note: the current NEN 1010 does not name a fixed universal power value (in kW/kVA) above which a separate circuit is mandatory — that is a project-specific assessment of the "high connected load". An earlier edition of the standard (NEN 1010:2015, at the time via a specific kitchen-appliance provision) once used a fixed 2 kVA threshold for a comparable situation; that fixed threshold no longer appears as such in the current standard. Do not assume a fixed figure, but base your assessment on the actual connected load of the chosen appliance.

Characteristic: compressor inrush current

A heat pump contains a compressor that draws a higher inrush current at start-up than its rated operating current. For regular domestic loads (lighting, small appliances) a B-characteristic circuit breaker is sufficient. For equipment with a significant inrush current — including heat pumps, but also solar panel inverters and electric vehicle charging points — a C-characteristic is more often used in practice, to prevent unwarranted tripping at start-up (see also the B/C/D characteristics guide).

Residual current device: type A is not always sufficient

A regular type A residual current device detects alternating current and pulsating direct current components. A modern heat pump with a frequency-controlled (inverter-driven) compressor can, however, cause a leakage current with a high-frequency and/or continuous direct current component that a type A RCD does not reliably detect. For that type of equipment a type B residual current device is indicated — the same consideration that already applies to electric vehicle charging points and certain PV inverters (see the RCD guide).

Note: whether a specific heat pump actually requires a type B RCD depends on the internal switching principle (the type of rectifier/ inverter) of that specific appliance — consult the manufacturer's installation manual rather than assuming a general rule for "every heat pump".

Common mistakes

1. Connecting a heat pump to a shared circuit with other equipment without assessing the connected load — with a high connected load §510.4.2 requires its own final circuit.
2. Sticking with a type A residual current device "because that's the standard", without checking the manufacturer's documentation for a type B requirement in the case of an inverter-driven compressor.
3. Sizing only for the rated operating current and ignoring the compressor's inrush current when choosing the circuit breaker characteristic.

Related

• Residual current devices (RCD)
• Circuit breaker characteristics B, C and D