A FUSE is a short length of thin, fusible alloy wire mounted in a fuse box between the mains supply and house circuit. It is designed to melt if the wires of the circuit become overloaded, thus cutting off the current before overheating causes fire or damage elsewhere. The occurrence of a ‘blown’ fuse therefore has to be taken at its true value: it is a safeguard against serious mishap.
The location in the house of the fuse box, or boxes (there may be two or more), should be known. In addition to the house circuit fuse boxes there is a mains fuse box, which the electricity supply company has sealed and which must never be interfered with by the consumer. This is on the street or inlet side of the meter, and is the concern only of the company’s sen-ants. The consumer’s principal fuse box, to which the householder can attend as often as necessary, will generally be found close by the side of the meter, and there may be another, or others, elsewhere in the house.
Individual fuse boxes control their own particular circuits, so that a fault developing in one circuit will not necessarily affect the entire house. When a fuse blows, note should be made of the rooms affected. When once that is determined, searching for the fuse box concerned on any future occasion is eliminated.
Fuse wire, to replace that which has suddenly blown, should always be kept ready to hand. Supplies are obtainable from the electricity company or from a shop dealing in electrical appliances, and it is standardized for specific purposes. It is 5 amp. Fuse wire for household lighting, 10 amp. For heating, 15 amp. For power. No other kind of wire should be used as replacement for a blown fuse; neglect of this precaution may result, when a short circuit occurs, in the wires becoming overheated elsewhere, with dire consequences.
As a fuse box may be situated in a cellar, or in a dark cupboard below the stairs, a torch or lighted candle may be required to enable the trouble to be attended to. And as a fuse replacement in such circumstances is a two-handed job, the presence of someone to hold the light is a decided advantage. A small screwdriver, and a pair of scissors or pocket knife to cut a new length of fuse wire, complete the simple tools required. Before touching the fuse box, the main switch, which controls all points, should be turned off. All current, on the consumer’s side of the meter, will then be cut off and the job can be proceeded with in perfect safety. After the melted fuse has been replaced with new wire, and the fuse box has been left as one found it, the main switch should be turned on again. This is an obvious procedure which is sometimes overlooked.
When the supply of current has been cut off by the main switch, the fuse box may be opened. There are several types, but the principles of design are the same. The arrangement of a sound fuse should be carefully examined. It is then an easy matter to replace melted wire. The porcelain fuse blocks can be slipped out from top and bottom grips. When it is seen which wire has melted (and to discover this it may be necessary to twitch each wire in turn, gently with the screwdriver) top and bottom terminals should be loosened, and wire adhering removed. A length of new fuse wire is then cut of sufficient length to allow of one turn around each of the two terminals after it has been passed through the fuse block. The terminals are then tightened with the screwdriver and the block replaced. Some fuses, such as those, are separately enclosed, the cover being secured by a knurled nut. Fitting new fuse wire to this type of fuse is simple.
Every fragment of the ‘blown’ wire should be removed before any attempt is made at replacement, and no surplus ends of the new wire should be allowed in the fuse box; they should be snipped or cut off close to the terminal. It also makes for neat and secure fixing if the wire-loop runs in the direction in which the terminal screw is tightened. The temptation to use a thicker wire than is appropriate may present itself in the case of frequent fusings, but the danger of this has already been stressed. If a fuse gives repeated trouble and the cause of the latter cannot be traced, the supply company should be approached for skilled assistance.
When one light only fails in the house and the fuse has not blown, the fault lies with the bulb itself, or possibly with the lamp-holder, the flex connections, or the point switch. Each of these parts is liable to the occurrence of one defect or another, and it is good practice to examine everything thoroughly not only with the object of locating the fault but of obviating the possibility of other defects.
Test these possibilities in turn. Remove the bulb and try it in another holder which is known to be in good order. If it fails to light, the bulb is obviously defective and a new one is needed. If the replacement bulb gives no light, examination of-the holder or connections or point switch is needed, but before this is done the main switch should be turned off.
Sometimes, the lamp socket spring plungers may not be bearing on the two lead contacts on the lamp’s base, the springs actuating the plungers having become weakened. If this fault cannot be adjusted after the holder has been taken apart, a sound one must be substituted. Or it may happen that one of the two slots in the sides of the holder, wherein the projections near the base of the bulb should engage and be gripped, has partly broken away, this defect causing the bulb to be held other than squarely in the socket. In this case again, a new holder is indicated.
If nothing is wrong with the holder itself, the flex connections in the holder may be faulty. The connections need to be both clean and immovable, and it may be discovered that the flex wire has completely or partly broken at or close to a securing screw. If so, the short faulty portion should be cut away and the new end of the flex stripped of its covering. The bared wire should now be inserted in its correct terminal and the holding screw tightened up. It may be found advisable to treat both wires in the same way, so as to obtain equal length of ends.
A flex end is most easily bared of its covering by using a short sharp blade in such a way that only the covering is cut (at a point about ½ in. in from the end) the actual wire strands being untouched by the knife. A few extra seconds spent on this careful removal of the covering may save a further shortening of the wire due to the sharp blade partly severing the wire. Ragged threads of the material can be removed with scissors, and then the exposed strands of wire, now carrying no fragment of rubber or cotton, should be twisted between the fingers tightly, a ½ in. of the end then being bent sharply back. Thus compressed, the wire will be held without possibility of movement when the connection is completed. A flex end which appears to be in perfect order when examined may be failing to function because of corrosion or dirt; it should be scraped clean and bright and then replaced. This is more likely to occur in the case of an electric bell push-button when its fitment is an exterior one, than in the case of an indoor lamp; but the possibility where indoor fitments are concerned is always worth bearing in mind. The point switch controlling the sound bulb which refuses to light up (and for which failure no other cause can be found) should be examined, the cover being removed for that purpose. The contact arm may have become corroded, and in this case gentle scraping so that the metal is left bright, on both sides, should prove effective. Or the contact arm may have lost its springiness, or become bent, and a little careful work with a pocket knife or small screwdriver will probably restore it to working condition. Purchase of a new contact arm may be necessary. A switch can generally be depended on to give service over several years, but there comes a time when the inevitable wear asserts itself and the working parts are no longer efficient, and here the sole remedy is a new switch.
It is essential that the cause of a blown fuse should be found and put right, otherwise the fuse will melt again immediately the faulty part is used again, be it a light bulb, bell, electric iron, vacuum cleaner, fire, cooker, or a sewing machine. The cause may be the frayed ends of different wires touching each other, or a break in the wire caused by a length of flex becoming kinked or knotted when put away instead of being loosely coiled. With the current off, such a break can be found by passing the flex slowly between the fingers and bending it inch by inch, when a break in the wire will become apparent by the readiness with which the flex suddenly bends at one point. It should be cut through at such a point, the exposed ends securely joined, and each join separately bound around with insulation tape. Use fairly wide tape and a good overlap.