Ok sorry if I sound clueless here but I am doing college work designing a circuit. I want to use a radial socket circuit in twin and earth that covers an area of 60 m^2, the osg says in table h2.1 that a 32 A breaker with minimum 4 mm^2 CSA cable.
So I then do calculated known loads and assumed 200W loads for rest of sockets then I do design current Ib, this gives me a value of 17 A, which would mean a 20 A breaker is more appropriate, I don't do diversity for cable size since the loads can be unpredictable on socket circuit. So I use derating factors for grouping etc etc and that gives me a Iz of about 22 A. Then from that with in table 4d5 in the regs with method 103 I get It of 32 A with a correspong CSA of 6 mm^2. So this is where I am confused. one do I use, will it be the reccomended OSG values of 32 A and 4 mm^2 for areas upto 75 m or is it what I calculted as 20 A breaker with 6 mm^2 which sounds really to large.
What takes priority, can I just use the osg reccomendations or do I need to use the sizes I calculated? I mean what are the assumptions used in the OSG reccomendations?
Is OSG for a particault method (clipped direct) and no de rating factors etc etc. It's very confusing? The question would apply if I chose a ring circuit, what takes priority the OSG reccomendations or your calculations?
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So I then do calculated known loads and assumed 200W loads for rest of sockets then I do design current Ib, this gives me a value of 17 A, which would mean a 20 A breaker is more appropriate, I don't do diversity for cable size since the loads can be unpredictable on socket circuit. So I use derating factors for grouping etc etc and that gives me a Iz of about 22 A. Then from that with in table 4d5 in the regs with method 103 I get It of 32 A with a correspong CSA of 6 mm^2. So this is where I am confused. one do I use, will it be the reccomended OSG values of 32 A and 4 mm^2 for areas upto 75 m or is it what I calculted as 20 A breaker with 6 mm^2 which sounds really to large.
What takes priority, can I just use the osg reccomendations or do I need to use the sizes I calculated? I mean what are the assumptions used in the OSG reccomendations?
Is OSG for a particault method (clipped direct) and no de rating factors etc etc. It's very confusing? The question would apply if I chose a ring circuit, what takes priority the OSG reccomendations or your calculations?
Continue reading...
