The complexity of electrical loads found in many domestic, commercial and public buildings and the existing safety regulations, place a greater demand on the Skilled Person (electrically).

Methods of voltage and current control used for energy saving, rely on power electronics to alter and or chop the electrical supply – referred to as nonlinear loads. The specific technology employed in energy saving and control applications will determine the nature of the leakage current and the residual current generated under fault conditions.

Table 1: Equipment Requiring Special Types of RCCBs

Table 1 gives generic examples based on the installed technology used and the associated RCCB. The inverter manufactures installation instructions must be checked, with regard to advice relating to the minimum sensitivity and the Type of RCCB that can be used safely with their equipment. This should be referenced back to any specific requirements contained in the UK Regulations and Codes of practice, which may differ from the International standards.

Example: Heat Pump with VSD

If the building or part of the installation (Heat Pump) is on a TT supply, an RCCB may be required See Reg 411. Regulation 331: Inverters operating on 3 phase supplies must only be connected to circuits protected by Type B RCCBs. For single phase inverters refer to the manufacturer’s instructions with regard to the Type of RCCB, as individual designs determine the Type of RCCB required e.g. A, F or B.

RCCB Checklist

Complex residual currents flowing under fault conditions require more complex RCCBs to safely detect the fault current e.g. Type AC RCCBs subjected to smooth DC leakage currents will not effectively sense AC leakage current under fault conditions.

Operational leakage currents for nonlinear loads can be significantly higher than conventional equipment, and must be taken into account when designing the installation. RCCB tripping current (sensitivity) must be selected based on the operational leakage currents, and the load circuits’ sub divided if necessary to prevent unwanted tripping – see regulation 531.2.4

Table 2: Refer to the Manufacturer of the Electrical Equipment for the Type of RCCB required.


For information on specific applications and RCCB selection, go to Doepke Web site – link to Technical Articles

Chaz Andrews – Technical Manager, Doepke UK Ltd or