First, let’s get rid of the myth. Just because in the last X amount of years fuses have not been blowing or tripping does not mean that the electrical installation must be okay. A fuse or circuit breaker is designed to:
- In the first instance protect the cables from overload. Let me expand on that for a moment. When a circuit is designed, the current drawn by the equipment (load) is determined and a cable is selected in accordance to that load. I think that everyone understands that the bigger the load a circuit requires, the bigger the cable must be. But, a small cable, say one used for lighting and fused at 6 amps, will carry a bigger load, for example a 16amp heater. The difference is, when a circuit is designed at its full load capacity, it is designed so that the copper conductors, in a PVC cable, run at 70 degrees Celsius. By limiting our lighting circuit as in our example above to 6 amps we are ensuring that the conductors do not get too hot, melt the PVC covering, or start a fire. We must also understand that a fuse or circuit breaker is a thermal device designed to melt or break if the temperature of the circuit goes above 70 degrees. However, all fuses will take some time to do this and so for short durations will allow more current through than the design current.
- Afford protection from leakage to earth, including short circuit.
The British Standards recommend that all electrical installations are inspected and tested regularly, to determine, so far as is reasonably practicable, whether the installation is in a satisfactory condition for continued service (Regulation 651.1). How often depends on the installation, the environment and the recommendation from the previous inspection, but it is usually every five years for most existing installations. For commercial installations, with many distribution boards, where the recommended interval between testing is 5 years, 20% can be carried out each year. This will allow for budgeting and minimising down time.
Buried in the small print of most, if not all commercial and landlord insurance, will be the clause that the cover is dependant on the property being well maintained and in safe condition. How do you know if the installation is safe if it is not regularly checked, an electrical MOT, to give it a regular analogy? You certainly can not prove it is well maintained if you have not records and test data.
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