From: wwm@wwmartin.net   
      
   On 2/27/26 14:25, Liz Tuddenham wrote:   
   > wmartin  wrote:   
   >   
   >> On 2/27/26 01:25, Liz Tuddenham wrote:   
   >>> Brian Gregory  wrote:   
   >>>   
   >>>> On 22/02/2026 19:59, Liz Tuddenham wrote:   
   >>>>> Brian Gregory  wrote:   
   >>>>>> With all good safely made brands of HRC fuse it means the fuse should   
   >>>>>> stay intact if the peak current is under 30kA, and exceeding 30kA is   
   >>>>>> likely to cause the fuse to explode and potentially damage other parts   
   >>>>>> of the equipment it is a part of.   
   >>>>>   
   >>>>> ...like the venetian blind slats on the other side of the room (yes, it   
   >>>>> happened to me whlst testing equipment with the covers removed).   
   >>>>   
   >>>> Ouch!   
   >>>   
   >>> There was an earth strap hidden on the back of the fuseholder block and   
   >>> my workshop was quite close to the electricity substation.   
   >>>   
   >>> I only discovered the strap when I gathered up the remains of the   
   >>> fuseholders and pieced them back together.   
   >>>   
   >>>   
   >> I wonder how much current it took to vaporize a 2KW wirewound resistor?   
   >> It had something to do with a pressurized waveguide that developed a   
   >> leak and arced internally... Impressive, nothing left but the metal end   
   >> cylinders!   
   >   
   > I once (well twice, actually) had to rebuild a starting controller for a   
   > 5 kW repulsion-induction motor.  Water had got onto the resistors and   
   > caused an arc to the earthed retaining bolts.  The slate core had   
   > shattered and the windings had exploded into short lengths (some with   
   > welded blobs on the ends).  Parts of the brass bolts had vapourised too   
   > - it must have been quite spectacular.   
   >   
   > The fragments of wire were so short that I had to use 4-terminal   
   > measurements to calculate the resistance values.  A resistance wire   
   > supplier in N.E. England recognised the type of wire immediatley and   
   > sold me the length I needed.   
   >   
   > A slate quarry in Cornwall cut me some replacement slate bars and I   
   > re-wound the resistors by hand, complete with tapping points for the   
   > various stages of motor control.   
   >   
   > The motor and controller were made in 1919 but I had no difficulty   
   > obtaining the materials to repair them and restore them to full working   
   > order.  The whole job onlu took about 3 weeks from start to finish.  How   
   > many modern electrical items will be so easy to repair in another 95   
   > years time?   
   >   
   >   
   Approximately none, they will all have been recycled for the precious   
   metal content!   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)