Hi All,
Was looking to buy a switchfuse today. I was looking at one which was perfect in all respects except one, it only takes them poxy 10 x 38 fuses...
What it is for is this; Imagine a length of 6mm SWA protected by a 40A MCB. At the other end of the SWA cable you have to fit a means of isolation, and terminate a 2.5mm flexible cable into it, that feeds a mechanical saw that draws about 15A. [Actually there are TWO saws]
Ok, so the saws, having a motors larger than 1/2 HP or whatever it is, are wired through a proper starter complete with thermal overload protection.
Now, left to myself, i would fit a switchfuse to each saw, with suitably rated gM fuses to give "backup" overload protection [for want of a better term] to the saw motor, and also overcurrent protection for the flexible cable leading to the saw, [both overload, [although the motor starter will already see to this] and fault current too.
Now, a gM fuse would be just perfect, but they do not seem to be available in 10 x 38 fuse sizes, all you can get are "aM" fuses.
These things do not provide overload protection, just fault current protection.. What is the point of that?? In the event of the 2.5mm cable being damaged, or a fault in the wiring of the machine causing "fault current" to flow, as Zs even at the end of the 2.5mm would still be sufficiently low, the 40A MCB at the origin of the SWA would operate anyway..
I was thinking of throwing away the fuse holders and fitting a TP, 16A, "C" curve MCB, which would have the added benefit, that, it would shut off all three phases in the event of overload or whatever, and prevent the numpty saw owners, from leaving the thing to carry on running on the two remaining phases and burning out even faster!!!!
Comments please!!
john..
Was looking to buy a switchfuse today. I was looking at one which was perfect in all respects except one, it only takes them poxy 10 x 38 fuses...
What it is for is this; Imagine a length of 6mm SWA protected by a 40A MCB. At the other end of the SWA cable you have to fit a means of isolation, and terminate a 2.5mm flexible cable into it, that feeds a mechanical saw that draws about 15A. [Actually there are TWO saws]
Ok, so the saws, having a motors larger than 1/2 HP or whatever it is, are wired through a proper starter complete with thermal overload protection.
Now, left to myself, i would fit a switchfuse to each saw, with suitably rated gM fuses to give "backup" overload protection [for want of a better term] to the saw motor, and also overcurrent protection for the flexible cable leading to the saw, [both overload, [although the motor starter will already see to this] and fault current too.
Now, a gM fuse would be just perfect, but they do not seem to be available in 10 x 38 fuse sizes, all you can get are "aM" fuses.
These things do not provide overload protection, just fault current protection.. What is the point of that?? In the event of the 2.5mm cable being damaged, or a fault in the wiring of the machine causing "fault current" to flow, as Zs even at the end of the 2.5mm would still be sufficiently low, the 40A MCB at the origin of the SWA would operate anyway..
I was thinking of throwing away the fuse holders and fitting a TP, 16A, "C" curve MCB, which would have the added benefit, that, it would shut off all three phases in the event of overload or whatever, and prevent the numpty saw owners, from leaving the thing to carry on running on the two remaining phases and burning out even faster!!!!
Comments please!!
john..