--- In firstname.lastname@example.org, Ian & Judy Jenkins <ianjudyjenkins@...> wrote:
Thanks, JeanLuc. ... the good Sergio ... sticks to a pretty basic rule which I have not seen written anywhere else--he always disconnects the negative wire first. Similarly, when connecting he always connects the positive wire first. Is this the correct sequence? it seems such an elementary point that I would have expected it to appear in any handbook on electricity. Cheers, Ian and Judy, Pen Azen, SM 302, Spain===========================
Ian & Judy,
This is all about eliminating sparks near the battery that could ignite hydrogen and cause an explosion. The rule comes from working with cars where the body and frame act as the negative wire (rare exceptions use positive "ground").
By removing the negative wire from the battery first you eliminate the risk of accidentally touching the positive wire to the frame when you remove it and causing a spark. Also elimiates risk of damage to electronics.
Much less of an issue on the boat, especially Amels because they use double pole disconnect battery switches (both the pos and neg wires are disconnected when you open (turn off) the battery switch.
Of course, if there's any load "on" there will be a spark when you connect the last wire to the battery, be it pos or neg, so be sure to turn off all breakers & battery switches beforehand.
A good practice, of course, is to be sure your battery area is well ventilated before working there.
Btw, you'll see this in Nigel Calder's books, in Xantrex inverter/charger instructions, etc.
Cheers, Craig & Katherine SN#68 "SANGARIS" in Mesolonghi, GR