EESS / Battery systems Iz of cable

Question I'm embarrassed to ask, you know the old "I should know that......" kinda thing. And kick myself when its explained...

But regarding EESS / Battery systems. where the current capacity of the cable and assemblies must be equal to all loads, for example 16A MCB plus 16A inverter means 32A Iz.
Maybe im being dumb, but why? Surely if inverter is running at full whack of 16A, current cant flow in both directions?

A student asked me this week and I was a little stumped, which as a trainer is somewhat embarrassing!
Parents
  • There is more to this than meets the eye, as it depends where between the inverter and the incoming mains the loads connect.

    perhaps the inverter generates 16A max, and,  if in battery charging mode the current never exceeds16A then - so far so good,a cable for 16A ( or the larger of the two) is suitable.

    But perhaps that connects to a dis board or CU  on a sub main  with another load attached - so the supply cable and fuse feeding into that could see that load + or - 16A, and needs to be rated for the sum.

    Except if it is a house CU then the input fuse is 100A, the inverter may add another 16 - should the internals of the CU be rated for 116A ? perhaps !
    Mike

Reply
  • There is more to this than meets the eye, as it depends where between the inverter and the incoming mains the loads connect.

    perhaps the inverter generates 16A max, and,  if in battery charging mode the current never exceeds16A then - so far so good,a cable for 16A ( or the larger of the two) is suitable.

    But perhaps that connects to a dis board or CU  on a sub main  with another load attached - so the supply cable and fuse feeding into that could see that load + or - 16A, and needs to be rated for the sum.

    Except if it is a house CU then the input fuse is 100A, the inverter may add another 16 - should the internals of the CU be rated for 116A ? perhaps !
    Mike

Children
  • Why stop at that? 16 A from the roof, 16 A from the battery and 100 A from the mains?

    Once again, it depends upon where the supplies join.

    132 A for a house seems a lot. What is in there - a cannabis factory?

    I appreciate that CoPs and standards must change with time, but the laws of physics do not.