Cable Calculations Steps Flashcards
To learn them off by heart and be confident. (22 cards)
What does Ib represent?
Load current.
What does In represent?
MCB rating current.
What does Iz represent?
Cable current carrying capacity.
What is the first step for cable calculations and what equation is used to help you?
To find the load current and the equation P=VI is used.
What is the second step?
To select a protective device which has to be higher than the load current.
Say/write down the IEC MCB ratings within the 230V range.
1, 2, 3, 4, 6, 10, 13, 16, 20, 25, 32, 40, 50, 63, 100 and 125 Amps.
What is the 3rd step and what table helps you find it?
To determine the installation method if not given to you. Table 52 A.3
What is the 4th step, the symbol associated with it, and the tables where you can find the info?
To determine the temperature facture. Symbol is Ca and tables 52 B14 - 15 are used.
What is the 5th step, the symbol associated with it and the tables where you can find the info?
To determine the grouping factor. Symbol is Cg and tables 52 B17 - 21 are used.
What stays true for temperature and grouping factor?
If not given to you, assume a value of 1.
What is the 6th step, the tables used and the equation associated with it?
To determine the cross sectional area using tables 52 B.2 - 13. The equation is It = In divided by (Ca x Cg)
How is It used to find cross sectional area?
Iz has to be greater than or equal to It and you’d use that knowledge to locate csa in the appropiate table.
How many cores do single phase multicore cables have?
Two cores.
How many cores do three phase multicore cables have?
Three cores.
What is the resistivity of copper?
0.0225 Omm^2.m^-1
What is the resistivity of aluminium?
0.036 Omm^2.m^-1
Write down the voltage drop equation.
u = 2IbL(p1/s (0.8) + 0.000048)
Write down the voltage percentage equation.
Voltage drop = u/U0 (x100)
What should you do if the voltage percentage exceeds the circuit maximum percentage allowed?
Choose the next highest cross sectional area to the one originally selected. The larger the csa, the lower the V drop because more current will flow.
What is the amps per watt rule of thumb?
Roughly 4A per kW.
What is the percentage drop maximum for lighting circuits and other types of circuits?
3% for lighting circuits.
5% for other types of circuits.
What is PVC and XLPE referred to in the cable calculations tables?
PVC: Thermoplastic insulated.
XLPE: Thermosetting insulated.
