An electrical short circuit is the most common cause of accidental fires in domestic, commercial and industrial buildings. Several recent fires in garment factories in Bangladesh drew the attention of the international media.
Foreign garment buyers are becoming increasingly critical about the safety of garment workers in Bangladesh. Many of us are not aware that most accidental fires in buildings can be prevented if a few precautions are taken when wiring a building for electricity.
Let us start with a simple example to explain as to how short circuits occur and how they cause fires. To light a normal filament bulb, we connect it to two electric wires at two different voltages.
When we switch on, a current passes through the filament of the bulb, which is heated to a point where it emits light. The filament has a resistance, which restricts the flow of current through the wires.
If we now connect another similar filament bulb in parallel with the first bulb, the current passing through the wires will be double.
Similarly, if we continue to connect more bulbs in parallel, a heavy current will flow through the wires. At this point, an excessive current will pass through the wires. This is an electrical short-circuit, an abnormal connection of two wires at different voltages of an electric circuit resulting in excessive current. At one point the wires may produce sufficient heat to catch fire.
Had there been a fuse or a circuit breaker in the system to disconnect the bulbs from the main line when the current exceeded a certain safe limit, the flow of current would have automatically stopped and there would have been no short circuit or fire.
The fuse or the circuit breaker is a protective device to isolate a load from the circuit when the current exceeds a safe limit.
A short circuit could even be cause by a single bulb for any number of other reasons.
The lessons come down to these important points. First, an electric circuit must have a protective system. Second, the load at any point of the circuit must never exceed a safe limit. Third, the wires, the switches, protective devices etc must be of good quality. Fourth, there should be no loose contacts in the circuit. Fifth, no live wires, switches, sockets etc with poor insulation should come in contact with any conducting material connected to the ground. Sixth, all metal parts of buildings should be earthed. Seventh, all buildings must be fitted with lightning arresters.
We should always remember that electrical wiring is the job of a professional. It is, therefore, important to employ an electrical engineer or a professional/certified electrician to design, lay, test, modify, extend or repair electrical distribution systems in any house, office or factory.
Care should be taken in procurement of cables, switches, circuit breakers, sockets, conduits and other electrical items so that they adhere to the highest safety standards.
No sub-standard material should be used in electrical circuits. Applicable codes of electrical wiring must always be followed. Bangladesh National Building Code (BNBC-1993) adequately covers all aspects of electrical wiring of buildings.
Under no circumstances, should a novice or apprentice electrician be allowed to fiddle with the electrical distribution systems of a building.
Special care should be taken when laying electrical lines in areas where combustible gases/materials are used, stored or manufactured.
All electrical connections must be made very carefully to eliminate the existence of loose contacts in the circuit.
Leakage of current can also cause accidental fires. Poor insulation or damp walls usually causes current to leak. Dampness of walls and conduits should be checked regularly. If any dampness is detected, the main switch should be switched off and the causes of dampness removed.
All houses, offices and factories should be equipped with fire detectors, fire fighting devices and fire exits. If there are frequent trips of circuit breakers, heating of cables, smoke, or any smell of burning cables in any building, the main switch must immediately be shut off, and should not be put on unless the whole circuit has been checked by a professional electrician and the causes of the fault or faults have been removed.
Electrical wiring including the protective devices, switches and sockets should be checked at regular intervals. Routine insulation tests, continuity and conductivity tests, cross-sectional area-check of cables is helpful in detecting faults in the electrical wiring.
We should remember that precautions cost very little but negligence can cost a fortune. The probability of fires caused by electrical short circuits in buildings can be significantly reduced if the simple instructions mentioned above are strictly followed.