Published:
8 October 2012
Category:
Technical articles
Where the armouring of a steel wire armoured cable is interrupted by a non-metallic enclosure, continuity of the armouring must be maintained where fault protection is provided by the protective measure of Automatic Disconnection of Supply
When continuity of the armouring is not maintained through a non-metallic enclosure, downstream metallic parts of the installation may rise to line voltage under fault conditions.
In such circumstances, the voltage can remain undetected posing a risk to persons contact with live parts.
Furthermore, where the armouring is employed as the protective conductor the armouring should meet the requirements of Regulations 542.2.4 and 543.2.5 for electrical continuity and cross-sectional area.
Where an armoured cable connects to a non-metallic enclosure equipment, such as an all-insulated luminaire, then as for any type of connection, Regulation 526.1 requires the connection to provide durable electrical continuity and adequate mechanical strength and protection. One method of maintaining continuity would be to connect a suitable conductor of adequate cross-sectional area between the glands of the armoured cable and the earthing terminal of the point of accessory.
(i) Its electrical continuity shall be assured, either by construction or by suitable connection, in such a way as to be protected against mechanical, chemical or electrochemical deterioration.
In such circumstances, the voltage can remain undetected posing a risk to persons contact with live parts.
Solution
Where an armoured cable is selected as (or forms part of) a wiring system, BS 7671 requires the armouring be effectively earthed. (Regulation 411.3.1.1 refers).Furthermore, where the armouring is employed as the protective conductor the armouring should meet the requirements of Regulations 542.2.4 and 543.2.5 for electrical continuity and cross-sectional area.
Where an armoured cable connects to a non-metallic enclosure equipment, such as an all-insulated luminaire, then as for any type of connection, Regulation 526.1 requires the connection to provide durable electrical continuity and adequate mechanical strength and protection. One method of maintaining continuity would be to connect a suitable conductor of adequate cross-sectional area between the glands of the armoured cable and the earthing terminal of the point of accessory.
Regulation 411.3.1.1 (part of)
Exposed-conductive-parts shall be connected to a protective conductor under the specific conditions for each type of system earthing as specified in Regulations 411.4 to 411.6.Regulation 526.1
Every connection between conductors or between a conductor and other equipment shall provide durable electrical continuity and adequate mechanical strength and protection.Regulation 543.2.4 (part of)
Where a metal enclosure or frame of a low voltage switchgear or controlgear assembly or busbar trunking system is used as a protective conductor, it shall satisfy the following three requirements:(i) Its electrical continuity shall be assured, either by construction or by suitable connection, in such a way as to be protected against mechanical, chemical or electrochemical deterioration.