"Matt" wrote in message
...
Andy Champ wrote:

Matt wrote:
NO NO NO

Always connect the earthed connection last and remove first

I've often heard this said. Why?

Also never complete the connection in the vicinity of the
battery i.e
don't ever use the -ve battery terminal
Hydrogen?


Because the first wire you connect is NOT a problem (unless the
bodies
are touching) You could drop the clips onto the body or anywhere
and
not cause a "flash" Then when you connect the 2nd wire, at the
"good
vehicle" end then its still a relatively safe situation as you can
easily connect to the "flat battery vehicle" preferably on an earth
strap well away from the battery terminals as if a spark occurs it
will be away from explosive hydrogen that may be around the battery
(its a slim chance)

Do it the other way round, earth first and you always have a +ve
terminal to connect last and usually this can only be done at the
battery, drop the jump lead in the engine bay of the "flat battery
vehicle" and you may get a big bang and a screwed up electrical
system
on the "good vehicle" also as you connect to the "flat battery
vehicle" you might get a spark and explode the hydrogen again.

Of course if you've done it loads of times you connect both wires
to
the good battery, walk to the flat one and connect the +ve one a
second or two before you do the -ve one and all is well
........until
the day you get distracted, put the clips on the floor, then there
is
a spark and the leads start smoking and glowing, the good vehicle
revs
drop and the alternator blows, the battery explodes and showers
everyone with acid.


....and just why would the battery explode, the alternator will cease
to output after the regulator vaporises, the leads might start to
glow but the battery will just discharge - as all you are doing is a
(servier) load bank test - it won't do the battery much good but it's
extremely unlikely to cause it to explode.

There is some utter clap-trap in this thread, most of you are
clueless as to the real risks and what are very slim possibilities or
'old wives tales'...

I'm not going to bother explaining but most of you are clueless as to
how to use jump leads correctly and are likely to do more damage to
one or both of the cars electrical systems - leave well alone or be
very afraid!