selecting a suitable size cable and CPC - using diversity

Question 1

step 1

Answer 1

calculate IB. IB = POWER / UO ( line - earth voltage )

if using diversity then go to APPENDIX A of OSG - A2

Question 2

step 2

Answer 2

IN - protective device. IN has to be greater then iB.

Question 3

step 3

Answer 3

iT - is the amount of current the cable needs to be able take and is iN divided by correction factors In APPENDIX4

Question 4

now we need to select a cable.

all to do with how the cable dissipates heat.

Answer 4

if twin & earth go to page 409 of bs7671. e.g 6mm

Question 5

if volt drop included in question

Answer 5

to to V.D section of table 4D5 & include to mv/a/m X LENGTH X IB divided by 1000

Question 6

use appendix I of OSG. pg 196

Answer 6

r1+r2 = r1+r2 tab from table i1 X length X factor (e.g) cables bunched on table i3

Question 7

incorporate the equasion on page 92. T = K X S divided by T ( all squared )

Answer 7

t - duration in seconds
k - a factor
s - cross sectional area of conductor in mm
I - fault current.

Question 8

earth fault loop path in tncs.

Answer 8

current will flow down the line , through fault down to the cpc , from cpc to MET through the neutral link as its a protective earth and neutral conductor , through the windings , completing the circuit.