Evening chaps, theoretical situation for my own interest / learning purposes and to check my assumptions / calcs.
One item on a ring final (protected by a B32 breaker) is an FCU with a 13A BS1362 fitted to it whos output is 2.5mm2 T+E radial that feeds 4 double sockets.
Fuse type correction factor:
Fusing factor for the BS1362 is 1.9 compared to 1.45 for a type B. Therefore tabulated cable rating needs to be:
13A x 1.9 / 1.45 = 17.03A
No grouping:
Therefore tabulated cable rating:
17.03 / 1 = 17.03A
On the wall in the garage:
Ambient temp assumed to be 30degC:
Therefore tabulated cable rating:
17.03 / 1 = 17.03A
2.5mm2 clipped direct has a rating of 27A so suitable.
In the loft:
Ambient temp assumed to be 50degC worst case:
Therefore tabulated cable rating:
17.03 / 0.71 = 23.99A (is 0.71 correct for the fuse type, I see some records point to 0.87 for non 1.45 fuse factor devices)
Cable laid over 100mm of rockwool with 200mm of rockwool on top of it for 3m length. Reference method 103 or clipped direct x 0.5 assumed.
2.5mm2 = 13.5A which is too low
4mm2 = 17.5A which is fine at a 30degC ambient
10mm2 = 32A is the smallest cable with a valid rating at 50degC
Have I screwed my calcs / made any bad assumptions?
This isn't my day job, I work on the electronics / product design end of the world and I'm just interested in how the above is calculated by the pros.
One item on a ring final (protected by a B32 breaker) is an FCU with a 13A BS1362 fitted to it whos output is 2.5mm2 T+E radial that feeds 4 double sockets.
Fuse type correction factor:
Fusing factor for the BS1362 is 1.9 compared to 1.45 for a type B. Therefore tabulated cable rating needs to be:
13A x 1.9 / 1.45 = 17.03A
No grouping:
Therefore tabulated cable rating:
17.03 / 1 = 17.03A
On the wall in the garage:
Ambient temp assumed to be 30degC:
Therefore tabulated cable rating:
17.03 / 1 = 17.03A
2.5mm2 clipped direct has a rating of 27A so suitable.
In the loft:
Ambient temp assumed to be 50degC worst case:
Therefore tabulated cable rating:
17.03 / 0.71 = 23.99A (is 0.71 correct for the fuse type, I see some records point to 0.87 for non 1.45 fuse factor devices)
Cable laid over 100mm of rockwool with 200mm of rockwool on top of it for 3m length. Reference method 103 or clipped direct x 0.5 assumed.
2.5mm2 = 13.5A which is too low
4mm2 = 17.5A which is fine at a 30degC ambient
10mm2 = 32A is the smallest cable with a valid rating at 50degC
Have I screwed my calcs / made any bad assumptions?
This isn't my day job, I work on the electronics / product design end of the world and I'm just interested in how the above is calculated by the pros.