Bellow is a schematic diagram of RCD:
Construction site installation: On this site, heavy equipment were used therefore proper and safe electrical installation must be carry out. Cable with full mechanical protection must be used such as Armour cable, minerals insulation cable and more sensitive control devices in case if there is any fault, they will easily trip off. It can happen to carry out the work in a wet area, which is dangerous to deal with electricity around the place due to the moisture. Also concerning the layout of the cables, since heavy machines are always moving around the area, underground cable with proper digging must be done, so that heavy equipment cannot penetrate to layout cables.
Protection against over-current:
This can be divided into two:
-Overload current: which can happen as a result of short-circuit between lives conductors. It can found in motor starting, inrush current and connecting more than the required load to the fuse rating. It can also found in earth fault current, this occurs between phase and earth.
-Fault current: is normally happen, if there is mechanical damage to circuits or accessories producing insulation failure or breakdown.
In case of the rewirable fuse, care must be taken for replacing it, consider the load and size of wire to use. If the wire has big cross-sectional area and the load is small during electrical fault fuse will not cut-off.
Protection against under-voltage:
It can be happened more especially in motor circuit to have under-voltage, in this case, the protection is provided by the contactor coil via the control circuit. And in the case of the computer system with IT GADGETS, Uninterrupted power supplies (UPS) need to be installed.
We have two important terms in protection system:
-Isolation.
-Switching.
Isolation: This is done through the use of isolator, which is a mechanical device that provides the function of cut-off the supply. It can be automatic or manually.
Switching: Are means of making or breaking supply, but only for the particular circuit.
Inspection and Testing:
Electrical inspection is an inspection, a visual check; a 'competent person' inspects the electrical installation of a premise by means of inspection.
Inspection is necessary to make sure all the connection was correct by visual means.
Testing:
It is conducted with electrical testing equipment to confirmed state of each device and electrical connections. Through the testing, you can know if there is continuity in a circuit which means power supply can be delivered safely and correctly. All the testing has its own procedure, some without supplying current while some after connecting the supply to the load. It is good and safe to consult the competent electrician to carry out the test.
