OP
- Reaction score
- 5
To use the above example of a feed from a CU with spurs off to individual lights. If the supply to the first light branches off at JB1, second at JB2, etc:
For light 1, total VD = VD from CU to JB1 + VD from JB1 to light 1.
For light 2, total VD = VD from CU to JB1 + VD from JB1 to JB2 + VD from JB2 to light 2.
For light 3, total VD = VD from CU to JB1 + VD from JB1 to JB2 + VD from JB2 to JB3 + VD from JB3 to light 3.
and so on.
If the CU is any significant distance from the origin of the installation, add the VD for the submain (at the expected maximum loading) to each distribution value.
The VD in each section of cable is calculated on the mV/A/m, actual current and length of that particular section.
When you've calculated the total VD at each load point, the VD for the whole circuit is just the maximum value of those figures. It's likely that you can omit calculating the VD for some of the loads by 'guessing' which will have the highest VD. ie one of the loads at the far end is likely to have the highest VD, unless one of the other spurs is particularly long or heavily loaded.
Yes. So I'm right in saying, you take worse case scenario for the circuit. Ie end of line. Or heavily loaded/long spur. Not an accimulation of every spur and supply cable. Just worse case route. And of its sarisfactory there then we can assume all other lengths/loads are fine.