XPost: sci.electronics.equipment   
   From: CFKinsey@military.org.jp   
      
   On Fri, 17 Jul 2020 23:07:43 +0100, Ralph Mowery    
   wrote:   
      
   > In article , rich@example.invalid says...   
   >>   
   >> I suspect you would find changing the range switch while connected is   
   >> much more common than your response implies.  Esp.  for switching   
   >> up/down a range for meters that are not auto-ranging.   
   >>   
   >> >> 2) By having the amps jacks separate, the range switch itself does not   
   >> >> have to have contacts beefy enough to carry the current for the amps   
   >> >> settings.  Remember, when measuring amps, the current being measured   
   >> >> flows *through* the meter itself.  This would require very different   
   >> >> (and likely much more expensive) range switch contacts.   
   >> >   
   >> > Or a relay.   
   >>   
   >> Which also equates directly to added expense vs.  having the user   
   >> themselves be that "relay".  And for battery powered meters, shorter   
   >> battery life (due to the current consumed by the relay coil).   
   >>   
   >> It is also possible (this is a guess in my part) that the CAT ratings   
   >> specify separate amps jacks for an added safety factor of "user must   
   >> deliberately move lead to obtain short circuit through meter".   
   >>   
   >> As well, the user who'd leave the leads plugged into amps, and then try   
   >> to measure voltage on car battery or other high current source is also   
   >> just as likely to leave the range switch in the amps setting (after   
   >> having measured current somewhere) and subsequently try to measure   
   >> voltage.  It is not possible to fully protect users who don't pay   
   >> attention from doing stupid things.  Either they forget to unplug from   
   >> the amps jack, or they forget to switch away from the amps range,   
   >> either way they get a local fireworks display of their own doing.   
   >   
   > I often leave the leads connected to a Simpson 260 and change voltage   
   > ranges.  Where I worked there were so many wires in a conduit carrring   
   > 120 VAC control voltage it was difficult to tell if the voltage was   
   > 'real' or induced by the coupling.  I found out that if I started on the   
   > 500 volt range and then switched to the 250 volt range if the meter   
   > pointer stayed in the same relative position I could then switch to the   
   > 50 volt range and the meter pointer would still be near the same   
   > relative position if the voltage was induced.  If the pointer changed   
   > positions to follow the 120 VAC when going to the 250 volt scale the   
   > voltage was real.   
      
   Better to use something that draws bit of current, like one of those   
   screwdrivers that lights a neon through your capacitance.   
      
   > I doubt that the CAT rating requies seperate Amps positions for the   
   > leads.  Fluke uses special fuses in their meters to get the CAT ratings.   
   > They do not have a seperate jack for the ohms settings either which is   
   > more likely   where the meter would be set.  Most of the time the   
   > circuit would have to be broken and the meter inserted to measuer amps.   
   >   
   > As you say it is impossiable to fully protect everyone from doing   
   > somethen forgetful or stupid, but having a $ 300 meter instead of a $ 5   
   > dollar one goes a long ways.   
   >   
   > I do have a Fluke test meter that is purty much fool proof up to 600   
   > volts and rated CAT 4. A T1000.  It only measuers AC amps by passing a   
   > wire through the prongs.  It does have a switch for voltage and ohms.  I   
   > have on purpose set it to ohms and put it across a fuse in a 480 volt AC   
   > circuit to see if the fuse is good or bad.  No problem to do this.   
      
   With a bad fuse it doesn't blow up?   
      
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