As a welder in many shops with different backgrounds including heavy truck
body fabrication and truck trays as well as light vehicle trays and other
light vehicle work i can confirm that it is common established practice in
all shops to disconnect the negative terminal at least, and in some places
the positive also. For most trucks, and many light vehicles in the mining
sector they have a battery isolation switch for safety and turning that off
is sufficient.

Having your earth clamp as close as possible to the weld is also common
practice, or at least having it in the opposite direction of the
electronics. Stray current is hard to predict though, so far better to
isolate the battery. Provided earth is removed and all electronics were
installed correctly, this is the safest way.

Shaun

"Brent" wrote in message
oups.com...
On Jul 21, 3:23 am, "Leo Lichtman"
wrote:
"JR North" wrote: On cars, clamping next to the weld is risky,

^^^^^^^^^^^^^^^^^^^^
No, that is the right way to do it. What you DON'T want to do is put the
ground clamp somewhere else, for two reasons: 1.) Don't give the
welding
current a return path that could include any electronics. 2.) Don't
give
the welding current a path that includes any bearings. Disconnecting the
battery is not necessary--the welding current isn't going that way, and
wouldn't hurt the battery if it did. The battery can handle hundreds of
amps easily. And you are right: disconnecting the battery could cause
you
to have to reprogram a bunch of stuff, including your radio stations and
the
radio's antitheft lockout.

If reprogramming is NOT the issue the disconnecting the negative
battery terminal (Which is recommended for my car) will leave in
theory every circuit open and as sunch not ABLE to pass welding urrent
through them.

I've heard of an instance where a stainless exhaust was installed
without disconnecting the negative battery terminal. After the system
was TIG'ed in the car wasnt running right and it eventually required
the replacement of the computer to blow it.

I'd rather reprogram a radio than replace an ECM Computer

Brent
Ottawa Canada