Understanding the final positions of the protection devices | a nap


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NAPIT Technical Director Trevor Milner discusses the final positions of protective devices to guard against failures. Regulation 434.2 describes how to achieve fault protection using downstream devices, stating that: “A device providing protection against fault current shall be installed at the point where a decrease in the cross-sectional area or any other change results in a decrease in the current carrying capacity of the conductors, Except where regulation 434.2.1, 434.2.2 or 434.3 apply. Risk Reduction The three conditions set out in Regulation 434.2.1 aim to reduce the risk of a fault and, in the event of an error, the risk of fire and danger to persons or property. The following measures are envisaged: 1. Use of conductor lengths that are as short as possible (3m max).2. Installation methods to reduce the risk of error, such as enclosure, container or cable type 3. Reduce the danger to people or the risk of fire. The intent is to reduce the risk of failures greater than bearing conductors, and to locate conductors or enclose conductors so that, in the event of a failure, there is a risk of fire or danger to persons or property through the emission of flames, arcs, or heat. Particles are prevented as far as practicable. When using metal enclosures or baffles, they must be connected to the protective conductor of the circuit. Supplies between the main switch, busbar and switch fuses where the conductors between the busbar chamber and the switch fuse are not of sufficient current carrying capacity to meet the busbar current rating, is a common example of this arrangement. Insufficient Space As such, there is a situation where the busbar and connections made to switch the fuse may not have enough space to install a suitable overcurrent protection device. In Figure 1, the busbar and associated switchgear, containment conductors have maintained integrity with respect to protection against ingress of foreign substances, compliance with Chapter 41, protection against shock, and Chapter 42, protection against thermal effects. BS EN 60439-1 specification for tested and partially tested assemblies requires that the manufacturer specify in its documents or catalogs the conditions, if any, for the installation, operation and maintenance of the assembly and the equipment in it. Where necessary, the above documents should indicate the recommended extent and frequency of maintenance. If the designation and installation are not clearly indicated due to the nature of containing the equipment provision of conductors, then the circuits and connections should be provided in the form of wiring diagrams of circuit descriptions. For more information about enrolling in the NAPIT program, click here


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