Because as everybody keeps quoting on here:
What size cable for a 32A radial ?
- Thread starter SUNRAY
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Because as everybody keeps quoting on here:
Well, yes, but as long as something satisfactorily protects the cable, then something else doesn't have to.
In fact circuit calculators do not provide a 2.5mm²/32A MCB combination.
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Think of it the other way round.
If the circuit MCB protects the cable then most 13A plug fuses in a domestic situation probably aren't actually required.
Most appliances probably can't cause an overload and the MCB will also protect the flex from fault current.
I once blew a 60A main fuse with a 1mm² CPC with no damage apart from a little blob on the end.
If the circuit MCB protects the cable then most 13A plug fuses in a domestic situation probably aren't actually required.
Most appliances probably can't cause an overload and the MCB will also protect the flex from fault current.
I once blew a 60A main fuse with a 1mm² CPC with no damage apart from a little blob on the end.
Well in that case , Why don't we do away with costly MCB's and run 2.5mm radials straight off the RCD to each individual sockets?
Protective devices are, indeed, there to 'protect the cable', but what seems to being overlooked here is the difference between overload protection and fault protection of a cable (both of which must be adequate).
Overload protection can be provided either upstream of the cable or, if the cable has adequate fault protection, downstream of the cable (or, indeed, not necessarily 'at all', if the nature of the load is such that it is 'unlikely to create an overload').
Fault protection always must be upstream of the cable being protected but, in the case we're discussing, a B32 MCB is more than adequate to provide fault protection to a 2.5mm² cable.
In passing, there is essentially nothing we can do to protect cables against 'faults' which are not 'of negligible impedance', but that's just a fact of life and, fortunately, an extremely rare happening.
Kind Regards, John
Overload protection can be provided either upstream of the cable or, if the cable has adequate fault protection, downstream of the cable (or, indeed, not necessarily 'at all', if the nature of the load is such that it is 'unlikely to create an overload').
Fault protection always must be upstream of the cable being protected but, in the case we're discussing, a B32 MCB is more than adequate to provide fault protection to a 2.5mm² cable.
In passing, there is essentially nothing we can do to protect cables against 'faults' which are not 'of negligible impedance', but that's just a fact of life and, fortunately, an extremely rare happening.
Kind Regards, John
Because the cables would then not have the required fault protection, since the only OPD involved (the DNO's cutout fuse) would almost certainly not be adequate to provide adequate fault protection for a 2.5mm² cable (and an RCD would provide no protection against an L-N fault).
Kind Regards, John
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I personally don't really see a problem where there is a fuse at the destination which there is with a double socket and the cable is of a size where a short circuit would operate a protection device at the origin. However the BS7671:2008 has a 3 meter rule.
However if that applies it also applies to any other spur from a radial or ring.
For the umpteenth time:
The three metre rule only applies where there is inadequate fault protection and then protection against fire is required.
The three metre rule only applies where there is inadequate fault protection and then protection against fire is required.
No. As the reg you posted says, one only has to satisfy (i) or (ii) - so, if there is adequate fault protection (which there will be), then there is no '3 metre rule'.
Kind Regards, John
Edit: typed too slowly again
and pressumably a black deposit somewhere.
working from memmory 60A TC fuse wire is 17swg, again from memory 16swg is a bit over 1.6mm dia and equally 18swg over 1.2mm dia assuming 17swg sits in the middle at 1.4+ the csa will be around 1.5mm².
My expectation is the fuse and the 1mm² would rupture equally assuming the PFC is well in excess of 300A and it is not predictable which week spot in the 1mm² will rupture depending on the nature of the fault of course. It is also remotely possible the 1mm² could rupture without the fuse on overload or if the PFC is too low for the 60A fuse.
Without checking the appropriate tripping curves.
No - 0.7mm² according to BS7671.
The weak spot was the fuse.
Well, it wasn't a bolted connection.
The wire just sprang out my hand and the end found the Main Switch incomer Line screw.
Bang - and as I said just a little blob on the end of the CPC.
Unless the size of fusewire has changed since I was intimately aware of the sizes in swg I feel your figure of 0.7mm² is well undersized. I don't have regs here to double check.
0.7mm² is approx 1mm dia. Again from memory 1mm is around 19swg & something like 35/36A
Assuming for now my memory of fusewire size is somewhere near correct then 1mm² cpc is smaller than 60A fuse wire, in the event of a fault I would expect both the fuse and the cpc to rupture. The fact that it wasn't 'terminated' will make further rupture not so predictable. I assume you checked the integrity of the cpc before repowering.
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