AN ELECTRIC FUSE

Manawatu Times, Volume XLXI, Issue 3480, 14 December 1926, Page 9

AN ELECTRIC FUSE

No Mystery About It

A SIMPLE AND USEFUL EXPLANATION

There is really no mystery about an electric fuse, as the following notes will reveal. It is a precautionary measure adopted in all electrical installations.

With many people, says a writer In “The Unit,” the fuse has always been associated with something mysterious hi the electrical installation of the house. They have a vague idea what it la there for, and how It operates, until one day something happens and the fuse is “blown.’ An electrician is sent for, the offending piece of apparatus is repaired, and everything goes on all right again. As a matter of fact an electric fuse is really a kind of safety-valve, a most remarkable piece of apparatus, fitted to prevent the wires of the lighting and power circuits and the lamps in the house from being damaged by excessive currents. It actually consists of a short piece of wire of special quality with a low melting point, and If for any reason the electrical circuit is overloaded with current the wire melts quickly and, of course, automatically breaks the circuit; the current ceases to flow and the whole circuit is then rendered “dead” or harmless. All Risks Reduced. A fuse is specially designed to reduce all risks of fire, shock, etc., to a minimum, but it is essential that a thoroughly reliable fuse of the correct size should be fitted, otherwise there is no advantage in using them. For example, if the fuse wire itself is too thick for the excessive current to melt it, the whole object of the fuse is defeated. The modern electric fuse is now enclosed, the actual fuse wire being in an insulated chamber, which protects the hand of the operator from coming into contact with the live wire when the fuse is being repaired. In some designs the fuse wire and metal contacts are mounted behind a porcelain shield fitted wfith a handle which enables one to remove the whole apparatus with perfect safety, and to insert easily a new fuse wire. Other designs are made on what is known as the cartridge principle, each fuse wire being insulated in a separate cartridge; but W'hatcver pattern is used care should be "taken to see that it comes from a maker of repute.

Practically every electrical installation is protected by a main fuse close to the electricity meter, where the supply comes in from the mains. This main fuse is generally made of copper, and should it for any reason be blown the whole house will, of course, be in darkness. Therefore, it is now usual to fit each branch of an electric lighting installation with a fuse of suitable size, usually of some alloy, or in some makes pure silver, which melts more easily than the copper of the main fuse, so that should this particular branch circuit become overloaded, the branch fuse is the first to blow, and not the main fuse. How to Repair a Fuse.

The repairing of ' a fuse is really quite a simple matter. The fuse bos or shield is removed (taking care tirst to switch off the current at the main switch), and the broken or melted wire. A fresh piece of wire is then Inserted between the two terminals, and the fuse box or shield is x-eplaced. The one essential, however, is to ensure that the new wire is of proper capacity. If, for example, a too heavy wire is used the melting point is raised to such an extent as to defeat the whole object of the apparatus. On the other hand, if too thin a wire is Inserted the household will be constantly troubled with the fuse blowing on a current which, though excessive for that class of fuse wire, is not too strong for the circuit itself. This, however, is made impossible in the modern cartridge type of fuse referred to above, in which the correct size of wire is ihserted by the makers. If these simple precautions are taken there is little danger of anything happening in the way of fire. The origin of the hackneyed phrase: “It is stated that the outbreak was due to the fusing of an electric wire,” is probably to be found in the old-fashioned type of fuse used in the early days, which consisted of a bare wire connected between two terminals on an insulated base. This practice lent itself rather to the using of an odd piece of wire of unsuitable composition or thickness, which proved not only unsuitable, but unsafe in an accidental rush of current. As mentioned above, this cannot happen with the cartridge typo of fuse, and in the type referred to above a small disc appears in the centre of each cartridge, coloured to indicate the current carrying capacity. When the fuse blows the indicator is thrown forward.