Fuses

The one that matches its fuse holder: glass fuses in equipment are usually 5 x 20mm or 6 x 32mm, while a plug or fused spur takes a BS 1362 cartridge fuse such as the Knightsbridge SN13AFUSE, 25.4mm long. Measure the old fuse or read the equipment marking, then match the type and current rating as well. The Mercury 787.010UK and 787.137UK are 1A slow blow fuses in the two glass sizes.

A quick-blow fuse breaks as soon as the current passes its rating, while a slow-blow fuse tolerates a short surge, such as the start-up current of a motor or transformer, before it blows. Mercury makes the two types in 5 x 20mm and 6 x 32mm glass. Examples are the 787.017UK 5A slow blow and the 787.267UK 5A quick blow; replace a fuse with the type it had.

A BS 1362 cartridge fuse such as the Knightsbridge SN13AFUSE, rated to suit the appliance rather than simply the 13A maximum. The SN13AFUSE is 13A, 25.4mm long and 6.35mm across, the SN3AFUSE is 3A, and the SNMIXEDFUSE set holds three 3A, three 5A and four 13A fuses. The SN13AFUSE, SN3AFUSE and SNMIXEDFUSE are ASTA approved.

Ratings include 100mA, 500mA, 1A, 2A, 5A, 10A and 16A in 5 x 20mm slow blow, and quick blow fuses reach 20A in the two sizes, as the 787.273UK and 787.342UK show. Fit the rating stated on the equipment or in its manual, never a higher one, because a larger fuse may not blow before a fault overheats the wiring.

Mercury listings such as the 787.263UK and 787.341UK state compliance with IEC 127, sheets 1 and 11, which covers miniature glass cartridge fuses. The Knightsbridge SN13AFUSE and SN3AFUSE plug fuses are certified to BS 1362 instead. Check the marking on the old fuse if a specification names a standard.

Packs of 10 for the glass and plug fuses: the Mercury glass fuses come ten to a pack, as do the Knightsbridge SN13AFUSE and SN3AFUSE, and the SNMIXEDFUSE set holds 10 fuses of three ratings. The Elmdene ELM-FUSE-KIT is larger, with 45 fuses of quick-blow and slow-blow types for fire and security equipment.

Switch off and find the fault before fitting another, because a fuse that blows at once usually points to a short circuit or a faulty appliance. Check that the replacement matches the original's type and rating: a quick-blow fuse fitted where a slow-blow one belongs can blow at switch-on. Never fit a higher rating to stop it blowing.

Yes, the Elmdene ELM-FUSE-KIT is a fire and security fuse kit of 45 fuses, including quick-blow and slow-blow types, for servicing fire and security equipment. For single replacements, Mercury glass fuses cover the same two types in 5 x 20mm and 6 x 32mm sizes. The 787.254UK, for example, is a 250mA quick blow fuse.