Cable Calculations - Diversity Applied

I have a room where the lights are all on or all off through presence detection. I anticipate that within a typical day the lights will be on 6 hours. That is 25% of the day. Does this mean that I sould insert for this specific circuit an individual diversity factor of 0.25?

I've no idea of the Amtech side of things, but from a general principle point of view, I think there's not enough informtion to say. My thinking is that it's down to how the pattern of usage maps onto thermally equivalent current - i.e. how much the load warms the cables (and equally overload protection devices) - which depends not only on what proportion of the day it's on but how long each on period is. Conductors take time to warm up - at full load perhaps something in the region of ten minutes for small sizes (e.g. 1mm²) or maybe closer to an hour or two for larger sizes (say 16mm² or 25mm²) at their full load. So if your 25% of the day was say 6 hours on and 18 hours off then after an hour or two of on time all the conductors will likely have warmed up just as much as they would have with a continuous load - so there's not really any scope for applying diversity at all. On the other hand if it's a pattern on 1 min on and 3 mins off then the conductors will hardly get any warmer than if you had a 25% load running constantly - so a diversity of 25% would be fine. Naturally your situation will be somewhere between the two and probably with a fair amount of uncertainty, which doen't make it easy to give a simple answer.


    - Andy.

I have a room where the lights are all on or all off through presence detection. I anticipate that within a typical day the lights will be on 6 hours. That is 25% of the day. Does this mean that I sould insert for this specific circuit an individual diversity factor of 0.25?

I've no idea of the Amtech side of things, but from a general principle point of view, I think there's not enough informtion to say. My thinking is that it's down to how the pattern of usage maps onto thermally equivalent current - i.e. how much the load warms the cables (and equally overload protection devices) - which depends not only on what proportion of the day it's on but how long each on period is. Conductors take time to warm up - at full load perhaps something in the region of ten minutes for small sizes (e.g. 1mm²) or maybe closer to an hour or two for larger sizes (say 16mm² or 25mm²) at their full load. So if your 25% of the day was say 6 hours on and 18 hours off then after an hour or two of on time all the conductors will likely have warmed up just as much as they would have with a continuous load - so there's not really any scope for applying diversity at all. On the other hand if it's a pattern on 1 min on and 3 mins off then the conductors will hardly get any warmer than if you had a 25% load running constantly - so a diversity of 25% would be fine. Naturally your situation will be somewhere between the two and probably with a fair amount of uncertainty, which doen't make it easy to give a simple answer.


    - Andy.