Low-voltage electrical installations - Part 4-43: Protection for safety - Protection against overcurrent

Overview

IEC 60364-4-43:2023 is one of the protection-for-safety parts of the low-voltage electrical installations series and covers protection against overcurrent. It sets requirements for protecting live, PEN, PEM and PEL conductors against the effects of overcurrent. Prepared by IEC TC 64, the fourth edition was published on 19 July 2023, runs to 67 pages and replaces the 2008 edition. The standard is therefore one of the core references for selecting cables and protective devices.

The most visible change in the new edition is its restructuring. Automatic disconnection of supply is designated the preferred measure for overcurrent protection. Other measures were moved to normative Annexes A, B and E for restricted applications. The main text thus concentrates on automatic disconnection, the most common solution in practice, and positions the alternatives as exceptions usable only when their conditions are met.

A further novelty is the new requirements for protecting the neutral or mid-point conductor. They treat the cases with and without triplen harmonics separately. Because SMPS-type IT loads in data centres can generate such harmonics, this part matters particularly for sizing the neutral conductor. Selecting the neutral at the same cross-section as the phase conductor may not be adequate under such loads, so the new requirements should be checked separately in the design.

The record rests only on the publisher's public abstract and product metadata; the full text of the standard was not read. Threshold values, tables and formulas are therefore not given here. IEC 60364-5-52, IEC 60909-0 and HD 60364-4-43 are named as related standards. Topics such as short-circuit withstand and selectivity lie outside the scope of this document alone and should be handled together with the relevant standards.

Key points

1. The standard sets requirements for protecting live conductors, including PEN, PEM and PEL, against the effects of overcurrent.
2. Automatic disconnection of supply is designated the preferred overcurrent protection measure.
3. Other measures were moved to normative Annexes A, B and E for restricted applications.
4. New requirements cover protection of the neutral or mid-point conductor, with and without triplen harmonics.
5. Edition 4 was published on 19 July 2023, has 67 pages and replaces the 2008 edition.
6. The standard is paid; this record rests only on the public catalogue abstract.
7. Related standards are IEC 60364-5-52, IEC 60909-0 and HD 60364-4-43.

Using it in design

• In cable and protection sizing, implement Ib <= In <= Iz and I2 <= 1.45 Iz style coordination checks together with short-circuit withstand.
• Size neutral conductors for the triplen harmonics typical of IT loads (SMPS).
• Add a rule that warns the designer when neutral current may exceed phase current.
• Use automatic disconnection as the baseline overcurrent solution and apply other measures only when their added conditions are satisfied.

Who should read it

Electrical design engineers sizing low-voltage distribution and cable-protection coordination.

Related standards

• IEC 60364-5-52
• IEC 60909-0
• HD 60364-4-43

Publication details

Authors

IEC TC 64

Publisher

IEC

Year

2023

Document number

IEC 60364-4-43:2023

Document language

English

Source type

Standard

Access

Citation only

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation