Cable rating factors?

[Johnny-G]

I understand how, when & why to apply C factors for cable selection etc. (I think!) but I can't get my head round why In is used in the equation for It and not Ib?

 

[Guest123]

Hi.

Well (In) as your OCPD rating will be the maximum current that can be drawn in that circuit. (Ib) is the design current of that circuit which will obviously be less than (In) and (It) the tabulated current carrying capacity of the cable must be higher than (In) after all the cable factors have been applied which is called (Iz).

 

[Johnny-G]

It's blindingly obvious when put like that, cheers