From: liz@poppyrecords.invalid.invalid   
      
   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?   
      
      
   --   
   ~ Liz Tuddenham ~   
   (Remove the ".invalid"s and add ".co.uk" to reply)   
   www.poppyrecords.co.uk   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)