Hi - I need some help with understanding the Regs with regards to selecting cable size when the tabulated cable rating has been worked out after applying the correction factors (It=In/CF's) Say a single core cable has thermal insulation surrounding it for most of it's length (method 4), such that Ci=0.5, and is protected by a 20A fuse (not 3036), then: It=20/0.5=40A now when looking up what cable size is suitable i.e. Table 41D1, should you select the cable size from the Method 4 column (thermal insulation), or the Method 1 column (clipped direct) ? Method 1, 40A cable = 6mm sq Method 4, 40A cable = 10mm sq in Brian Scaddan's book he chooses Method 1, however I've seen more or less the same example done differently in another book by using Method 4 as you might logically think was the way to do it. However - Method 1 would seem to make sense because the cable has already been derated by the calculation ? it's confused the hell out of me, which is the right choice ??!! many thanks in advance, got my 2381 exam tomoro
I think you're confusing method 4 with 'completely surrounded by insulation'. I read 523-04 as saying that you either use method 4 (in contact with thermal conductor on one side) OR you use the derate, applying it against method 1. As you say, applying both would be contrary.
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