Overloading and Fuse
Electricity produces heat as it travels through a conductor and a given amount of current will heat up a thin conductor more than it would a thick one. If too much current passes through a cable it will heat up to the point where it could damage the appliance or even cause a fire. This is what is known as overloading. To prevent overloading from causing harm or damage, a 'weak link' or 'links' known as fuses are introduced into wiring circuits and appliances. A fuse is made-up of a thin wire strand, designed to melt and break if the current passing through it exceeded the specified rating, so by breaking the circuit that stops the appliance from working. There are three types used in the home.
The Main Fuse
The main fuse is installed and sealed by the Electricity Board and is only accessible by them. This is a fuse that the householder need not be concerned about, as well as the fact that it rarely blows due to its high rating.
Consumer Unit Fuses
Consumer unit fuses are accessible to the householder and are located next to the electric meter. The type of consumer unit installed depends on how old the installation is and differ in the type of fuse system used. The most modern being are the 'miniature circuit breakers' (mbc). Mcb's are not fuses as described earlier, made-up of a thin wire, rather, as the name suggests, they are miniature switches or buttons that 'trip' if too much current passes through them. This type is the best, as they are very sensitive and to reset only requires flicking a switch or pressing a button. If there is a fault on the system, the switch will not reset.
Older consumer units have either a 'wire fuse' system or a 'cartridge system', both of which have removable fuse carriers that either contains a cartridge fuse or provisions for fuse wire to be installed.
Rectangular pin plugs use fuses of either 3, 5 or 13 amp. The fuse in a plug is designed to break the circuit to a particular appliance that it serves rather than a complete circuit, which means that the single appliance is isolated if a fault occurs, protecting the remaining circuit.
The fuse fitted to the plug must be relevant to the cable size on the appliance/device. If incorrect, the cable insulation could melt resulting in fire and/or electrocution in the event of a fault. For this reason, it is very important to know what size of fuses to use in the plugs that are connected to your appliances.
To determine the correct fuse size, the power rating (wattage) of the appliance must first be known, and this information should be displayed on the appliance itself. With the appliance wattage known, its rating should be divided by the voltage (230), so that an appliance below 700 watt would require a 3 amp fuse, an appliance below 1200 watts would require a 5 amp fuse, with a 13 amp for anything above this value.
Each fuse cartridge is colour coded as well as having the amp rating stamped upon it, the most common being 3 amp (red), 5 amp (black) and 13 amp (brown).
Continued on page 7