XPost: uk.d-i-y   
   From: harry130747@btinternet.com   
      
   "Gefreiter Krueger"  wrote in message   
   news:op.w60jrhnjiunomv@red.lan...   
   > When I moved in 13 years ago, there was a central heating system utilising   
   > only radiator stats.  I fitted a room thermostat (the basic bi-metallic   
   > strip variety), which connected live to the motorised valve, which in turn   
   > switched on the pump and boiler.  For some reason, it would often arc when   
   > switching off, which heated the bi-metallic strip up a little and it never   
   > managed to go off.  Problem solved by using an electronic thermostat which   
   > contained a relay, causing cleaner switching.   
   >   
   > Similar problem now, with the heating system extended so it does the   
   > garage, aswell as the house, with a seperate electronic thermostat.  The   
   > problem this time though, is because I could only find a motorised valve   
   > for the garage which did not have contacts inside it (only one which   
   > fitted my odd diameter of pipe), I had to fit a relay to switch the boiler   
   > and pump on and off (if I'd connected the output of the garage stat   
   > straight to the pump, boiler, and valve, then the valve would open every   
   > time the boiler and pump ran for the house too).  Anyway, it worked fine   
   > for a year, then the relay started behaving like the old bi-metallic strip   
   > thermostat - it arced when switched off, and took ages to do so, making an   
   > alarming noise.  So I replaced the relay with a big industrial contactor   
   > which is working for the moment.  The relay I replaced says it can take up   
   > to 2HP motors, way more than my pump.  Any idea what's going on?   
      
      
   Arcing is caused by stored emergy in the system (usually coils/electric   
   motors.)   
   You will often get a tiny spark when switching motors, this is normal and   
   not enough to affect a bimetal strip.   
   Most switches have a "snap action" to minimise this.   
   Just what do you mean by arcing?   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)