XPost: alt.home.repair, sci.electronics.repair   
   From: occassionally-confused@nospam.co.uk   
      
   micky  wrote:   
   > It had to do with accidentally ....aha it had to do with   
   > accidentally touching both cables to the frame of the car.  Say you've   
   > hooked it up to the car with the good battery, and then you connect the   
   > negative first.  Then while you're trying to connect the positive (and   
   > sometimes that's not easy. It has a cover or it's tucked away, or you   
   > can see it but can't get the clamp on, you touch the metal body or   
   > engine or frame of the car.  Now you have both cables touching the frame   
   > while at the other end, at the car you are using to jump your own, they   
   > are connected to a good battery.   Big spark.   
      
   Well. That makes sense. So maybe my initial reasoning was wrong that the   
   last cable attach will spark, and you want that spark away from the   
   battery, so that would have to be the negative cable.   
      
   However, you also said that the DISCHARGED battery is the one with all the   
   hydrogen, so that means that you want to put the donor battery cable on   
   last (because that's where the spark will be and the donor battery is   
   presumed to have less hydrogen outgassing).   
      
   But then you made a good point that if you put the positive on first, then   
   anything any negative touches by accident, will spark where it touched.   
      
   So now we have one good reason to put the negative on last and specifically   
   the negative on the DONOR car on last by one line of reasoning, and by   
   another line of reasoning, we have the positive going on last, presumably   
   also on the donor car because it's going to spark.   
      
   Which is the correct line of reasoning?   
      
   (A) Put the negative on the donor car last because that spark is least   
       likely to ignite hydrogen gases from the discharged battery   or   
   (B) Put the positive on the donor car last because you have less chance   
       of accidentally shorting the circuit & the donor has less outgassing   
      
   Which is more logical?   
      
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