Designing a distribution circuit to power board

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Active member
Apr 24, 2023
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Hi guys,
Here to bother you with another boring design question.

I am running through my design course and doing great so far.

I've just completed all of the required lighting circuits, so I'm good with Ib<In<It, calculating SWA as protective conductor, adiabatic requirements, etc.

I have one MainDB feeding two DBs, one for lighting and one for power.
I'm getting stuck designing the distribution circuits for the power boards (mix of 13a sockets, 63a TPN isolators, 32a isolators, etc..)

With lighting I have a certain amount of loads (e.g.. 100 x 25w lamps), drawing a certain amount of current (so my design current for the entire distribution circuit is 10.8A for single phase) then OCPD is easy, cable selection is easy (accounting for derating) and the rest is just following calculations...easy enough.

This is where I might be getting lost:
When I design a ring circuit, it's just an A1 circuit (from OSG), I can assume my design current for the A1 Ring would just be the In (discounting diversity)?

So, if I had say, 3 x 32A rings and 1x motor circuit with a Ib of 10A, then would my Ib for the distribution circuit be 106A before any diversity is applied?

Obviously, the Ib doesn't mean much when you are designing a single A1 ring as the circuit is already designed, but the whole distribution circuit situation means it must matter...right?

Thanks for any help lads