FusedConnection Unit : ( Accessories ) :26:
A fusedconnection unit is defined in BS 7671 as a deviceassociated with the fixed wiring of an installation by which appliances may beconnected, and having provision for a replaceable cartridge fuse link. Fusedconnection units manufactured to BS 1363-4 haveprovision for a BS 1362 cartridge fuse-link andare available with or without an integral switch.
Fusedconnection units have a nominal voltage rating not exceeding 250 V a.c. at afrequency of 50 Hz, and a current rating not exceeding 13 A. Fusedconnection units are classified as: • switched or unswitched • flush, surface or panel-mounting • with or without provision for an outgoing flexible cableor cord • with or without indicator lamp. Fusedconnection units should, amongst other things, be marked with: • number of the British Standard, that is BS 1363• rated current; that is 13 A• rated voltage; that is a.c. not greater than 250 V• nature of supply; a.c. only• incoming (in or supply) terminals• outgoing (out or load) terminals • symbols to identify whichterminals are line, neutral and earth.Theincoming (supply) line and neutral terminals of fused connection units aredesigned for the connection, without special preparation, such as twisting, ofup to three 2.5 mm2 solid or stranded copperconductors, or up to two 4 mm[SUP]2[/SUP] strandedcopper conductors. Theincoming earthing terminal is designed to permit the connection, withoutspecial preparation, of up to three 1.5 mm2 or 2.5 mm2 solid or stranded copper conductors, or of up to two 4 mm2 stranded copper conductors. Theoutgoing (load) line, neutral and earth terminals are each designed for theconnection, without special preparation, of one 1.5 mm2or 2.5 mm2 solid or stranded copper conductor. Whereprovision is made by the connection unit for the fitting of a flexible cord,one copper conductor having a nominal cross-sectional area of 0.5 mm2 up to and including 1.5 mm2 may beused. InstallationThedepth of accessory box should be such that the cables or conductors do notsuffer damage or cause stress to the terminals, (Regulations 522.8.1and 522.8.3refer). BS 1363-4 recommends that the depth of thebox should be such that there is a adequate wiring space. Fusedconnection units are supplied with a cord anchorage to enable the installer toprevent stress and strain on connections, as required by Regulation 522.8.5. SwitchingFusedconnection units are not designed for d.c.supplies and may only switch an a.c. supply. Aswitch fused connection unit is a double-pole device and may therefore be usedwhere it is necessary to switch both the line and neutral conductors, such asmight be the case where a step-up transformer is used (Regulation 555.1.3refers). Anunswitched fused connection unit is not a double-pole deviceand may not be used as such.Table53.2 of BS 7671 permits all fused connection unitsto be used as a means of isolation for TN systems by means of the removal of thefuse-link. Removal of the fuse-link of an unswitched fused connection unit,however, is not suitable for emergency switching or functional switching. The relevant aspects ofTable 53.2