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Cable Sizing for 2 nos x 400W Floodlight

Qaslun

I'm trying to design one single line diagram (just for learning session) and one of my circuit is having 2 nos. x 400W Floodlight with 1.5sqmm Cu/PVC cable, with 30m cable length, MCB rating 10A all the calculation such as load current Ib, MCB rating In, derating factor, cable carrying capacity and voltage drop is shown in the above photo.

Based on my calculation, my Ib < In < Iz is  3.9A < 10A < 17.5A respectively, with voltage drop of 3.933V @ 1.147% from 230V, 

However, after discussing this with several knowledgeable individuals and referring to previous single-line diagrams that I've encountered, they've indicated that 1.5sqmm might not be sufficient, instead they requested me to change it to 2.5sqmm. (I do understand 2.5sqmm is better than 1.5sqmm in terms of cable-current carrying capacity, and voltage drop).

My query is, where might my calculation have gone wrong in this context?  



  • in reply to Sergio Fernandez

    and if an RCD is to be useful in a lighting column impact scenario, it would have to be located before the post, rather than inside it - which would be tricky since they're typically cabled direct from the street mains.

    Additional protection is normally only useful where damage can expose live conductors without triggering ADS - (e.g. damage to soft sheathed cables) - with earthed steel conduit, MICC etc, that's pretty much impossible. Wiring inside an earthed/bonded steel lighting column would fall into a similar category I would have thought.

       - Andy.

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