Cooker calc

[rob1967]

Hi

Step 1: Ib = 12000/240 = 50A, diversity 10A + (30% of 40A) + 5A = 27A
So Ib = 27A

Step 2: In = 30A

Step3: I'd say in conduit and at an ambient of 45deg. I would not use any Cg or Ci figures as the worst factor compensates for them, this is done when there are combination of factors not all affected at the same time.

Ca = 0.79
Cg = 1
Ci = 1
30/0.79*1*1 = 38A

Step 4: Cable selected is 6mm with 4mm cpc using Ref Method B as the conduit is in the roof space not in an insulated wall! Therefore CCC of 41A.

Step 5: 7.3mV*27*25 = 4.93V = 2.05%

Step 6: Maximum Zs for 30A BS1361 is 1.15 ohms
R1 = 0.08
R2 = 0.12
ZS = 0.25 + ((0.08*0.12)*1.2) = 0.49 ohms

Step 7: csa = 2.74mm so the cpc complies.

I know this is an old subject but i think the calcs are fine but have noticed a few mistakes ( or I could be reading it wrong, if so sorry )

In step 3 the wost case would be the grouping factors as that is 0.60 ( 5 cables together) so
30/.60*1*1=50A

So step 4 would be select a cable of 10mm with a 6mm cpc from TABLE 4D2A, method C clipped direct........... Not sure if i'm right.............please can anyone tell me??