Classes for Twisted Pair Cabling

The ISO/IEC 11801 defines four classes for twisted pair cabling. These classes are based on the maximum frequency required for the application and is summarized as follows:

Class A: speech band and low frequency applications up to 100 KHz; it involves to Category 1 components and supports basic rate ISDN

Class B: low to medium bit rates for applications up to 1 MHz; based on use of Category 2 components and supports applications such as such as primary rate ISDN

Class C: medium data rate applications up to 16 MHz; utilizing Category 3 components and supports applications such as 10 Mbps Ethernet as used in 10 BASE T LAN’s

Class D: high data rate applications up to 100 MHz; utilizing Category 5e components and supporting applications such as 100BASE TX (100 Mb/s) and Gigabit Ethernet (l000Mb/s) LAN’s and ATM transmission @ 155 Mb/s

Class E: higher data rate applications using up to 250MHz of Bandwidth; and using Category 6 components.

Class F: higher data rate applications using up to 600MHz of bandwidth; and using Category 7 components.

Voltage Grades

You might notice there is indication of voltage grade (i.e 600/1000 volt) for every multicore cable. This voltage grade are conforming the metric British Standards for wiring cables.

The voltage grade of 600/1000 volt indicates that the cables are designed for a power frequency voltage to earth of 600 volts and a power frequency voltage between conductors of 1000 volts.

The metric Standard for flexible cords will include the voltage grades 300/300 volt and 300/500 volt.

The grade 300/300 volts indicates that the cord is designed for use on single phase systems where the voltage to earth and the voltage between conductors do not exceed 300 volts.

The grade 300/500 volt indicates that the cords are designed for use on systems where the voltage to earth does not exceed 300 volts and the voltage between conductors does not exceed 500 volts.

Comparison Between Single-Phase and Three-Phase System.

During the earliest day, the alternating current is mainly used for resistive load such as electric lamp and electric heater. That electrical load is resistive type whereby the use of single-phase system works well. However, when ac motor is developed, the single-phase system may not function well since the ac motor require higher starting torque for self-starting.

So what did they do? In order to make the ac motor to self-start, it is fitted with auxiliary winding but the problem is, there will always an alternating component with frequency that is double the frequency of power supply. This scenario is okay for small motor but it will cause a noisy and vibration during operation for a large motor.

Single-phase voltage source are originated from three-phase system. In a balance three-phase system, there are three sinusoidal voltage sources of equal amplitude and equal frequency of variation but out of phase with each other by 2π/3 or 120° but for single-phase system is only having one.

An important advantage of three-phase power supply is that three-phase motors have a non-zero starting torque as compared with the single-phase system.

The characteristic of three-phase system is the currents and voltages are balanced everywhere in the circuit. The most important property of such a circuit is that though the power in an individual phase is pulsating and varies at twice the supply frequency, the sum of powers delivered by all the phases is constant at every instant of time.