Standards Development

Scope

This document specifies the requirements and tests for the selection of RCDs (residual current devices) for AC system intended to be installed upstream of other RCDs, respectively called upstream RCD and downstream RCD in this document.

In this document, RCDs include: 

- residual current operated circuit-breakers without integral overcurrent protection (RCCB) according to IEC 61008 standards series and IEC 62423 if applicable,

- residual current operated circuit-breakers with integral overcurrent protection (RCBO) according to IEC 61009 standards series and IEC 62423 if applicable.

The tests described in this document apply to RCDs intended to be installed upstream. These tests are defined by considering the normative limits of the different types of downstream RCDs and considering the most unfavorable cases defined in this document.

The purpose of this document is to ensure that a specific RCD or a range of RCDs, of type AC, A, or F, can be installed upstream of any downstream RCD of type A and/or F and/or B and operates without failure.

Compliance with this document serves as the basis for manufacturers to provide instructions regarding the correct coordination of RCDs, as described in IEC 60364 -5-53:2019 /AMD1:2020, 531.2.3.3.2.

Selectivity between RCDs is out of the scope of this document. When RCDs are installed in series, both selectivity and coordination shall be considered according to IEC 60364 -5-53.

NOTE IEC 60364-5-53, 535.3, recommends a minimum ratio of 3 between the sensitivities of RCDs installed in series to ensure good selectivity in residual current (plus a type S). For example, upstream of a 30 mA RCD, it is advisable to install an RCD with a minimum sensitivity of 100 mA. This ratio of 3 is favorable to the coordination of RCDs of different types.

RCDs in prosumer electrical installations are covered by this document and do not require special consideration in terms of the coordination, whether in AC grid -connected mode or in island mode. An exception to this concerns dynamic earthing systems in isl and mode which may need further investigation.

NOTE This standard may be used as a guide for RCDs that comply with other product standards such as IEC 60947-2, future IEC 63464-1 etc.

Purpose

Different types of RCDs (residual current devices) for AC system are available on the market: type AC, type A, type F, and type B. They are described by the standards of IEC 61008 series for RCCBs or by the standards of IEC 61009 series for RCBOs. Type F or B RCDs are described by the additional standard IEC 62423.

These different types of RCDs are selected based on the waveform of residual current fault that may potentially occur due to the type of loads present on the line.

There are numerous examples where RCDs of different types (AC, A, F and B) can be installed in series. This raises the question as to the behaviour, particularly in the presence of residual DC current.

For example, a type B RCD with a rated residual current of 30 mA is connected in series with an upstream type AC RCD 300 mA. The type B RCD will trip in the presence of a DC fault current between 15 mA and 60 mA. Therefore, in theory, a fault current between 15 mA and 60 mA could be present at the upstream RCD. It is legitimate to ask to what extent this fault would disrupt the operation of the RCD placed upstream.

The purpose of this document is to define the necessary verifications to ensure the proper functioning of the upstream RCD in the presence of characteristic faults of a downstream RCD of type A, F, or B.