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Komise : IEC/SC 121A (Low-voltage switchgear and controlgear)
K připomínkám do: 22.04.2020
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This document covers internal arc-fault control devices, hereinafter referred to as IACD, which are intended to:

detect internal arc-faults in low-voltage switchgear and controlgear assemblies, by processing (at least) optical effect of an internal arc-fault, and

operate mitigation device (either external or combined)

in order to minimize the effects of the internal arc-fault (see Figure 1).

For the purpose of this document “light” or “optical” is covering more than visible spectra. They may cover also, for example, infrared or ultraviolet (see Annex D).

For combined-type IACD, this document shall be considered in addition to the relevant product standard for internal arc fault mitigation devices (IARD per IEC TS 63107:—). Compliance to the relevant product standard is mandatory and cannot be claimed regarding testing to this document alone.

NOTE 1 Low-voltage switchgear and controlgear assemblies are usually described by IEC 61439 series.


NOTE This figure displays a simplified IACD schematic with only one optical sensor and no other sensing means that can be used for secondary confirmation of an arcing fault, such as current sensing.


1   assembly enclosure

2   internal arc-fault

3   optical sensor

4   processing unit

5   trigger output used to operate e.g. mitigation device

Figure 1 – Optical-based IACD schematic (stand-alone type, no secondary sensor)

Therefore, this document covers the following:

arc-detection unit (stand-alone, multifunction or combined);

one or more associated sensor(s) used to detect optical effect of the internal arc-fault;

sensor(s), sensing another physical effect, to confirm the fault;

associated or combined mitigation device.

An IACD is not intended to trigger under normal operation of low-voltage switchgear and controlgear (i.e. absence of internal arc-fault), including normal arcing associated with operation of disconnecting and switching devices.

This document only covers the following methods:

optical detection of the light caused by an internal arc-fault;

optional confirmation of internal arc-fault by line current measurement.

Many different conductive materials could be used in LV assemblies (e.g. steel, copper, aluminium). Nevertheless, tests specified in this document are deemed to represent the most critical conditions for arc-detection and cover all combinations of materials.

NOTE 2 Compared to other materials (e.g. steel, aluminium), copper leads to a lower optical radiation energy.

The rated voltage of the assembly in which an IACD is installed shall not exceed 1 000 V AC.

Such devices are designed to be operated and maintained by skilled persons only.

This document does not cover:

DC internal arc-fault detection and control;

overcurrent relays;

AFDD (arc-fault detection devices) as defined by IEC 62606;

guidance on installation within assemblies;

NOTE 3 The integration of IACD into an assembly is described in IEC TS 63107 [1].

use with additional measures within explosive atmospheres. These are given in IEC 60079 series;

requirements for embedded software and firmware design rules; for this subject, the manufacturer is responsible for taking additional safety measures;

NOTE 4 IEC TR 63201 is describing rules for firmware and embedded software development preventing errors in software.

cybersecurity aspects; for this subject, the manufacturer is responsible for taking additional safety measures;

NOTE 5 See IEC TS 63208 [2].

mobile applications.

NOTE 6 Even when addressing internal arc-fault mitigation devices, this document does not supersede any other relevant product standard (e.g. IEC 60947-2 or IEC 60947-9-1).

NOTE 7 DC arcing fault phenomena are under consideration. However, further study is needed to comprehend DC arcing phenomena and required sensing.


[1] Future IEC TS 63107 ED1 is under preparation. Stage at time of circulation: PRVDTS.

[2] Under preparation. Stage at the time of circulation: APUB.