APPENDIX 08: Current-Carrying Capacity and Voltage Drop for Busbar Trunking and Powertrack Systems (487) Flashcards
Where can you obtain the voltage drop for a busbar system (Appendix 8, 5 p.488)
a) From the wholesaler
b) From the manufacturer
c) From Appendix 4
d) On Site Part 5 of BS7671
b) From the manufacturer
Appendix 8, 5 p.488
Voltage drop
The voltage drop (Vd) for the busbar trunking or powertrack system is obtained from the manufacturer. It is usually expressed as mV/ampere/metre, tabulated according to the value of the load-circuit power factor. The voltage drop given is calculated on the basis of a single load at the end of the run and, in this case, the total
voltage drop = Vd × Ib × L / 1000 volts, where L is the length of run in metres. (Ib = design current of busbar)
In the case of an evenly distributed load (tapped off at intervals along the busbar trunking or powertrack system) then the voltage drop at the furthest tap-off point may be taken as 0.5 Vd, and is calculated by the above method.
In the case of an unevenly distributed load it will be necessary to calculate the voltage drop for each section between tap-off points and add them together to find the voltage drop at the furthest tap-off point.
