2365 203 #19 - Cable Selection Factors

What is the main factor that determines the size of a cable?

• Voltage

• Length of the run

• Current-carrying capacity

• Insulation colour

What document contains current-carrying capacity tables for cables?

• Part P

• On-Site Guide and BS7671 Appendix 4

• Building Regs Part B

• GN3

What does “installation method” refer to in cable selection?

• Which company installs it

• How the cable is fixed or enclosed

• Time of day installed

• Number of sockets used

Which of these is a common installation method classification?

• Method 10

• C, E, F

• L, M, N

• R1, R2, R3

What does grouping of cables affect?

• Loop impedance

• Voltage output

• Heat dissipation and current-carrying capacity

• Earthing arrangement

What correction factor is applied for high ambient temperatures?

• Zs

• Ca

• Cg

• Cp

If you install multiple cables side-by-side, what must you do?

• Reduce the CPC

• Use twin-core instead

• Apply a grouping correction factor

• Lower the RCD rating

What is the “design current” (Ib)?

• The total load current expected

• The rated current of the fuse

• The breaker setting

• The RCD trip level

What is the protective device rating (In)?

• The test current for insulation

• The current at which the device is designed to operate

• The number of circuits in use

• The CPC size

What does Iz represent in cable calculations?

• Impedance rating

• The actual current the cable can safely carry

• The neutral resistance

• Loop impedance