Introduction: Fixed wiring (also called as conduit wiring or building wiring or house wiring, depending upon the application) in India now a days use copper wires with class 5 copper conductor. This is common not only in residential application, but industrial and commercial application as well. The reason is copper wires with class 5 conductor is cheaper in comparison to copper wires with class 2 conductor (approximately 8 % cheaper). On the other side these coper wires with class 5 conductor can bring disaster in a building as it increases the disconnection time of protective device due to its increased resistance. The power loss of class 5 conductor is higher and is against the concepts of energy conservation or sustainability.
Wiring with class 5 copper conductors do not conform to the code of practice of wiring and hence it's illegal to use them in fixed wiring.
Wires with class 5 copper are for appliance wiring and panel wiring. Hence, they are also manufactured. Its about 8 % cheaper than wires with class 2 copper conductor.
All types of cables, including house wires were imported into India from England till the year 1920. First cable factory was started in India in 1920. However, those cables were just single solid conductor (known as class-1 conductor now a days) having insulation over it. Subsequently innovations in wires were a necessity, as a result stranded conductor was introduced came in market.
Stranded conductor can be divided broadly in two types one is multi-strand conductor (known as class-2 conductor) other is Flexible stranded conductor (known as class-5 conductor). Multi-stranded conductor (Class 2 conductor) replaced single solid conductors for all the applications.
The cables used in Building wiring switched to Class 2 copper conductors as it offered better flexibility over the Class 1 solid copper conductors. It is also technically superior and avoid hot spots at bends without compromising the current carrying capacity on account of its resistance being the same as specified for Class 1 copper conductors.
The use of flexible cables for appliances wires and panel wiring as bending and routing of such cables in constricted paths do not yield stress on the cable constructed, also handling and installation of such conductors in confined areas is easier. Class 5, flexible cable and flexible cords are preferably used for connections to portable appliances and equipment where the lengths are preferably 1.5 to 2 m.
If we keep appliance wires aside and concentrate on fixed housing wires, it’s advisable to use cable multi-strand conductor (Class- 2). Below is the comparison to understand why cables with multi-strand conductor have edge over cables with flexible conductor.
Conductor resistance of copper based on class of conductor
Comparison of class 2 and Class 5 copper conductors
The demerits for use class 5 conductors as below,
The conductor resistance of class 5 is high compared to class 2 conductor, the heat generated for the same current loading will be different on both class of conductors
The insulation thickness for the class 5 conductor cable is lesser than specified for class 2, not better for higher load conditions
The mechanical strength of insulation for class 5 is lesser in comparison to class 2, this can lead to issues during conduit pull
Worldwide the usage of class 2 conductors is specified for building wires as it offers lower resistance, mechanical strength is higher.
Comparison of other paraments
Energy loss VS payback
The following calculations (approximate) shows that the payback in using (an expensive) class 2 conductor is less than 3 years.
For fixed wiring application conductors with Class 2 copper shall be used. This shall be specified by electrical designers in the respective tenders.
Class 5 wires have problems of higher watt loss, higher voltage drop, higher fault loop impedance.
Higher impedance of the circuit may lead to accidents due to higher disconnection time of protective device (e.g. OCPD)
Class 2 copper conductors produce approximately 8 to 9 % less heat (low losses) in comparison with Class 5 copper conductors. Less losses, more sustainable, safer.
Internationally class 2 wires are used for house wring.
Class 5 wires are used in India due to its reduced cost. (8 % less copper).
The authorities and government departments such as Electrical Inspectorates of state government / CPWD / PWD, etc shall ban the use of class 5 copper conductor in fixed wiring of Highrise, hospitals, industrial and commercial establishments.
Establishments such as IGBC and BEE shall make class 2 wire mandatory for "CERTIFIED GREEN BUILDINGS".