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
  • If you;'re thinking of 551.7.2  then (my interpretation) is that when a generator is installed on a circuit shared with loads and there's no control of the layout, then it is possible for both the current flowing into the circuit (e.g. from the grid) In plus the output from the generator (ig) to be flowing in the same direction at the same time towards the load, and so if there aren't any compensatory measures yes Iz would then have to be ≥ In + Ig.

    To apply the same logic to a circuit that supplies a single item of equipment which can be either a load (e.g. when charging) or a generator (when discharging) but can never be both at the same time, I think is illogical (but could be implied from the wording of the regulation).

      - Andy.

  • Indeed my confusion, they cant be going in both direction at the same time.

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